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  • ASME Material Specification and Grades for Pipes, Tubes, Forgings, Castings, Fittings, Valves, Nuts and Bolts

    ASME Material Specification and Grades for Pipes, Tubes, Forgings, Castings, Fittings, Valves, Nuts and Bolts

    For the complete identity of a material we need two things;

    1. Material Specification 
    2. Material Grade

    For Example, In SA 106 Gr.B the “SA106” is the material specification, and “Gr.B” is the grade of the material.

    Please note that for a particular specification there may be more than one grade. For example, SA106 has three grades i.e. Grade A, Grade B, and Grade C.

    In this article, The Material Specification & Grades has been explained, as per ASME Sec II, for the following Items/commodities;

    1. Pipes

    2. Tubes

    3. Forgings

    4. Castings

    5. Fittings

    6. Valves

    7. Nuts and Bolts

     

    ASME Material Specifications for Pipes:

    1. SA 53: Hot-dipped, Zinc-coated, Welded, And Seamless Pipes

    2. SA 106: Seamless Carbon Steel Pipe For High-temperature Service

    3. SA 312: Seamless, Welded, And Heavily Cold Worked Austenitic Stainless Steel Pipes

    4. SA 333: Seamless And Welded Steel Pipe For Low-temperature Service And Other Applications With Required Notch Toughness

    5. SA 335: Seamless Ferritic Alloy-steel Pipe For High-temperature Service

    6. SA 358: Electric-fusion-welded Austenitic Chromium-nickel Stainless Steel Pipe For High-temperature Service And General Applications

    7. SA 376: Seamless Austenitic Steel Pipe For High-temperature Central-station Service

    8. SA 409: Welded Large Diameter Austenitic Steel Pipe For Corrosive Or High-temperature Service

    9. SA 672: Electric-fusion-welded Steel Pipe For High-pressure Service At Moderate Temperatures

     

    Popular Grades for Pipes:
    Material Specification and Grade (ASME) P.No/Group No.
    SA 106 Gr.B P 1/1
    SA 672 Gr.B P 1/1
    SA 106 Gr.C P 1/ 2
    SA 335 P 11 P 4/1
    SA 335 P 12 P 4/1
    SA 335 P 22 P 5/1
    SA 376 TP 321H P 8/1
    SA 376 TP 304H P 8/1
    SA 376 TP 316H P 8/1
    SA 376 TP 347H P 8/1

     

    Material Specifications for Tubes:

    1. SA 179: Seamless Cold-drawn Low-carbon Steel Heat-exchanger And Condenser Tubes

    2. SA 192: Seamless Carbon Steel Boiler Tubes For High-pressure Service

    3. Sa 209: Seamless Carbon-molybdenum Alloy-steel Boiler And Superheater Tubes

    4. SA 210: Seamless Medium-carbon Steel Boiler And Superheater Tubes

    5. SA 213: Seamless Ferritic And Austenitic Alloy-steel Boiler, Superheater, And Heat-exchanger Tubes

    6. SA 249: Welded Austenitic Steel Boiler, Superheater, Heat-exchanger, And Condenser Tubes

    7. SA 556: Seamless Cold-drawn Carbon Steel Feedwater Heater Tubes

    8. SA 688: Seamless And Welded Austenitic Stainless Steel Feedwater Heater Tubes

     

    Popular Grades for Tubes:
    SA 179 P 1/1
    SA 192 P 1/1
    SA 210 Gr A1 P 1/1
    SA 210 Gr. C P 1/ 2
    SA 556 Gr C2 P 1/ 2
    SA 209 T1 P 3/1
    SA 209 T1a P 3/1
    SA 209 T1b P 3/1
    SA 213 T11 P 4/1
    SA 213 T12 P 4/1
    SA 213 T22 P 5/1
    SA 213 T5 P 5/1
    SA 213 T9 P 5/2
    SA 213 TP 321H P 8/1
    SA 213 TP304 H P 8/1
    SA 213 TP 304 P 8/1
    SA 249 TP 304 P 8/1
    SA 688 TP 304 P 8/1
    SA 213 TP 316 H P 8/1
    SA 213 TP 347 H P 8/1

     

    Material Specifications for Plates:

    1. SA 240: Chromium And Chromium-nickel Stainless Steel Plate, Sheet, And Strip For Pressure Vessels And For General Applications

    2. SA 299: Pressure Vessel Plates, Carbon Steel, Manganese-silicon

    3. SA 302: Pressure Vessel Plates, Alloy Steel, Manganese-molybdenum And Manganese Molybdenum-nickel

    4. SA 387: Pressure Vessel Plates, Alloy Steel, Chromium-molybdenum

    5. SA 515: Pressure Vessel Plates, Carbon Steel, For Intermediate-And Higher-temperature Service

    6. SA 516: Pressure Vessel Plates, Carbon Steel, For Moderate- And Lower-temperature Service

    7. SA 517: Pressure Vessel Plates, Alloy Steel, High-strength, Quenched And Tempered

    8. SA 204: Pressure Vessel Plates, Alloy Steel, Molybdenum

    9. SA 225: Pressure Vessel Plates, Alloy Steel, Manganese-vanadium-nickel

    10. SA 283: Low And Intermediate Tensile Strength Carbon Steel Plates

    11. SA 285: Pressure Vessel Plates, Carbon Steel, Low- And Intermediate-tensile Strength

    12. SA 353: Pressure Vessel Plates, Alloy Steel, Double-normalized And Tempered 9% Nickel

    13. SA 455: Pressure Vessel Plates, Carbon Steel, High-strength Manganese

    14. SA 533: Pressure Vessel Plates, Alloy Steel, Quenched And Tempered, Manganese molybdenum And Manganese molybdenum-nickel

    15. SA 537: Pressure Vessel Plates, Heat-treated, Carbon-manganese-silicon Steel

    16. SA 542: Pressure Vessel Plates, Alloy Steel, Quenched-and-tempered, Chromium-molybdenum, And Chromium molybdenum-Vanadium

     

    Popular Grades for Plates:
    Material Specification and Grade (ASME) P.No/Group No.
    SA 516 Gr 60 P 1/1
    SA 516 Gr 70 P 1/ 2
    SA 299 P 1/3
    SA 515 Gr 70 P 1/ 2
    SA 387 Gr 12 P 4/1
    SA 387 Gr 22 P 5/1
    SA 240 TYPE 321 P 8/1
    SA240 – TYPE 304 P 8/1
    SA240 – TYPE 316 P 8/1
    SA240 – TYPE 347 P 8/1

     

    Material Specifications for forgings:

    1. SA 105: Carbon Steel Forgings, For Piping Applications

    2. SA 181: Carbon Steel Forgings, For General-purpose Piping

    3. SA 182: Forged Or Rolled Alloy And Stainless Steel Pipe Flanges, Forged Fittings, And Valves And Parts For High-temperature Service

    4. SA 266: Carbon Steel Forgings For Pressure Vessel Components

    5. SA 336: Alloy Steel Forgings For Pressure And High-temperature Parts

    6. SA 350: Carbon And Low-alloy Steel Forgings, Requiring Notch Toughness Testing For Piping Components

    7. SA 372: Carbon And Alloy Steel Forgings For Thin-walled Pressure Vessels

    8. SA 723: Alloy Steel Forgings For High-strength Pressure Component Application

     

    Popular Grades for Forgings:
    Material Specification and Grade (ASME) P.No/Group No.
    SA 105 P 1/ 2
    SA 182 F12 P 4/1
    SA 182 F22 P 5/1
    SA 182 F321 H P 8/1
    SA 182 F304 H P 8/1
    SA 182 F316 H P 8/1
    SA 182 F347 H P 8/1

     

    Castings Material Specifications:

    1. Sa 216: Steel Castings, Carbon, Suitable For Fusion Welding For High-temperature Service

    2. Sa 217: Steel Castings, Martensitic Stainless And Alloy, For Pressure-containing Parts, Suitable For High-temperature Service

    3. Sa 351: Castings, Austenitic, Austenitic-ferritic (Duplex), For Pressure-containing Parts

    4. Sa 352: Steel Castings, Ferritic And Martensitic, For Pressure-containing Parts, Suitable For Low-temperature Service

     

    Popular Grades for Castings:
    Material Specification and Grade (ASME) P.No/Group No.
    SA 216 WCB P 1/2
    SA 216 WCC P 1/2
    SA 217 WC1 P 3/1
    SA 217 WC6 P 4/1
    SA 217 C 5 P 5/2
    SA 217 WC 9 P 5/1
    SA 351 CF 8 P 8/1
    SA 351 CF 8M P 8/1
    SA 351 CF 8C P 8/1
    SA 351 CH 20 P 8/2

     

    Material Specifications for Fittings:

    1. SA 234: Piping Fittings Of Wrought Carbon Steel And Alloy Steel For Moderate And High-temperature Service

    2. SA 403: Wrought Austenitic Stainless Steel Piping Fittings

    3. SA 420: Piping Fittings Of Wrought Carbon Steel And Alloy Steel For Low-temperature Service

     

    Material Specifications for Flanges:

    1. SA 105: Carbon Steel Forgings, For Piping Applications

    2. SA 182: Forged Or Rolled Alloy And Stainless Steel Pipe Flanges, Forged Fittings, And Valves And Parts For High-temperature Service

    3. SA 350: Carbon And Low-alloy Steel Forgings, Requiring Notch Toughness Testing For Piping Components

     

    Material Specifications for Valves:

    1. SA 216: Steel Castings, Carbon, Suitable For Fusion Welding For High-temperature Service

    2. SA 217: Steel Castings, Martensitic Stainless, And Alloy, For Pressure-containing Parts, Suitable For High-temperature Service

    3. SA 352: Steel Castings, Ferritic And Martensitic, For Pressure-containing Parts, Suitable For Low-temperature Service

    4. SA 182: Forged Or Rolled Alloy And Stainless Steel Pipe Flanges, Forged Fittings, And Valves And Parts For High-temperature Service

     

    Material Specifications for Nuts and Bolts:

    1. SA 193: Alloy-steel And Stainless Steel Bolting For High-temperature Or High-Pressure Service And Other Special Purpose Applications

    2. SA 194: Carbon And Alloy Steel Nuts For Bolts For High Pressure Or High-Temperature Service, Or Both

    3. SA 320: Alloy-steel And Stainless Steel Bolting For Low-temperature Service

  • ASTM A 36 Steel – Mechanical & Chemical Properties and Equivalent Steel Grades

    ASTM A 36 Steel – Mechanical & Chemical Properties and Equivalent Steel Grades

    ASTM A 36 or SA 36 is basically carbon steel of structural quality which is widely used in industries. It is also known as Carbon Structural Steel. ASTM A 36 is readily available in the following product form;

    • Plates
    • Bars
    • Shapes (beams, channels, angles, etc.)

     

    In this article following topics will be covered;

    1. Mechanical Properties of ASTM A36 steel
    2. Chemical Properties of ASTM A36 steel
    3. A 36 Steel Equivalent
    4. Other properties of A 36 steel such as Density, Melting Point, Modulus of elasticity (Young’s modulus), Shear modulus, Poisson’s ratio, etc. 

     

    Mechanical Properties of ASTM A36 steel:

    The mechanical properties such as Ultimate tensile strength, Yield stress, and % Elongation of A36 steel plates, shapes (beams, channels, angle, etc.), and bars are given in the below table;

     

    Mechanical Properties of A36 steel

    NOTE:

    1. For wide flange shapes, having flange thickness more than 75 mm (3 in), minimum % elongation in 50 mm (2 in.) will be 19 % and the 550 MPa (80 ksi) maximum tensile strength will not apply

    2. For plates with a thickness of more than 200 mm (8 in.), the minimum yield stress value will be 220 MPa (32 ksi)

    3. For plates with a width of more than 600 mm (24 in), the minimum % elongation requirement will be reduced to two percentage points.

     

    Chemical Properties of ASTM A36 steel:

    The chemical properties of A36 steel plates, shapes (beams, channels, angle, etc.), and bars are given in the below table;

    Chemical Properties of A 36 Steel

    Note: For shapes with flange thickness more than 75 mm (3 in.) – Manganese content required 0.85–1.35 % and silicon content required 0.15–0.40%.

     

    A 36 Steel Equivalent:

    Due to the varying amounts of chemical and mechanical properties, It is very hard to come to a conclusion for an equivalent of A36 steel from other standards. However, in general, the following steel properties are very near to A36 steel and hence can be considered comparable to A36 steel;

    • European Standard (EN 10025-2:2004): Equivalent Grade – S235JRG2
    • Canadian Standard (CSA G40.21-13): Equivalent Grade 260W
    • German Standard (DIN 17100): Equivalent Grade – St 37-2
    • Japanese Standard (JIS G3101): Equivalent Grade – SS400
    • Indian Standard (IS2002): Equivalent Grade – E250
    • Chinese Standard (GB 700-88): Equivalent Grade – Q235B
    • ISO Standard (630:1995 A1:2003): Equivalent Grade E 235 (Fe 360)

     

    Other properties of A 36 steel:

    Density:  7.85 g/cm3 (0.284 lb/in3)  

    Melting Point: 1425-1538 °C (2,600-2,800 °F)

    Modulus of elasticity (Young’s modulus): 200 GPa (29000 ksi)

    Bulk Modulus: 140 GPa (20300 ksi)

    Shear modulus: 79.3 GPa (11500 ksi)

    Poisson’s ratio: 0.260

     

     

  • Mechanical Properties of Materials

    Mechanical Properties of Materials

    The mechanical properties of the metals are those which are associated with the ability of the material to resist mechanical forces and loads. The topic of the mechanical properties of materials is of great industrial importance in the design of tools, machines, and structures. These properties are structure sensitive in the sense that they depend upon the crystal structure and its bonding forces (at the microstructural level), especially upon the nature and behavior of the imperfections which exist within the crystal itself or at the grain boundaries. In this article, we will discuss 13 main mechanical properties of the metals, these are;

    1. Strength
    2. Elasticity
    3. Plasticity
    4. Ductility
    5. Malleability
    6. Brittleness
    7. Stiffness
    8. Hardness
    9. Creep
    10. Fatigue
    11. Resilience
    12. Toughness
    13. Weldability

    These properties can be well understood with help of a stress-strain diagram (Given below). The Stress-Strain diagram is plotted with the help of a tensile test.

     

    Stress Strain Curve

     

    Now we shall discuss the 13 different mechanical properties of materials;

    1) STRENGTH: Strength is defined as the ability of a material to resist the externally applied load. The internal resistance offered by a material to externally applied forces is called stress.

    The capacity of resisting external loads by metal and to withstand destruction under the action of external loads against these stresses is known as strength.

    The stronger the material, the greater the load it can withstand this property of material, therefore, determines the ability to withstand stress without failure.

    Strength varies according to the type of loading like tensile, compressive, shearing, and torsional strengths. The maximum stress that any material can withstand before destruction is called it’s UTS or ultimate tensile strength (Point ‘D’ is the ultimate tensile strength (UTS) shown in the above figure). The tenacity of the material is its ultimate strength in tension.

     

    2) ELASTICITY: Elasticity is defined as the property of a material to regain its original shape after removal of the externally applied load. We can take an example of a rubber band, whenever we pull a rubber band it gets elongated i.e. it’s shape gets deformed but when we remove the load the rubber band comes back to its original shape. Hence we can say that a rubber band is an elastic material or rubber band exhibits the property of elasticity.

    When the external forces are removed it can also be referred to as the power of the material to come back to its original position after deformation. It can be used as an important application for building precision instruments like Springs or structures etc.

    Any material will exhibit the elasticity property up to a certain load which is called as the elastic limit of that material (the region between point ‘O’ and ‘A’, in the above stress-strain diagram, is the elastic range, it is also known as the proportional limit. Beyond point ‘A’ permanent deformation of the material will start). If we keep on applying the external load beyond the elastic limit, the material will be permanently deformed i.e. the material will not be able to regain its original shape even after the removal of the external load.

     

    3) PLASTICITY: Plasticity is defined as the property of material under which the material is not able to regain its original shape even after the removal of the load i.e. the material permanently gets deformed.

    In other words, It is the ability or tendency of a material to undergo some degree of permanent deformation without its failure.

    Plastic deformation takes place only after the elastic limit of material has been exceeded. This property is important in forming, shaping, extruding and many other hot or cold working processes materials such as clay lead, etc are plastic at room temperature and steel is plastic at forging temperature this property generally increases with an increase in temperature of materials.

    This property of the material is required in forging in stamping images on coins and in on mental work.

     

    4) DUCTILITY: Ductility is termed as the property of a material that enables it to be drawn into the thin wire with the application of tensile load.

    The ductility is usually measured in terms of percentage elongation and percent reduction in the area which are often used as empirical measures of ductility.

    In general, materials that possess more than 5% elongation are called as ductile materials

    The ductile material commonly used in engineering practice in order of diminishing ductility a mild steel copper aluminum, nickel, zinc, tin, and lead.

     

    5) MALLEABILITY: Malleability is the ability of the material which enables it to be flattened into thin sheets under applications of heavy compressive forces without cracking (by hot or cold working), which means it is a special case of ductility which permits materials to be rolled or hammered into thin sheets.

    A malleable material should be plastic but it is not essential to be so strong.

    The malleable materials commonly used in engineering practice in order of diminishing value wrought iron, copper and aluminum, lead steel, etc are recognized as highly malleable metals.

     

    6) BRITTLENESS: Brittleness is the opposite of ductility. It is the property of breaking of a material with little permanent distortion the materials having less than 5% elongation and the loading behavior are said to be brittle materials.

    Brittle materials when subjected to tensile loads snap off without giving any sensible elongation glass, cast iron, brass and ceramics are considered as brittle material thus brittleness is the property of a material to snap off without giving any sensible elongation when subjected to tensile loads.

     

    7) STIFFNESS: Stiffness is defined as the ability of a material to resist deformation under stress. The resistance of a material to elastic deformation or deflection is called stiffness or rigidity.

    Material that suffers slight or very less deformation and the load has a high degree of stiffness or rigidity for instance suspended beams of steel and aluminum may both be strong enough to carry the required load but the aluminum beam will sag or deflect further which means the steel beam is stiffer or more rigid than the aluminum beam.

    If the material behaves elastically with linear stress-strain relationship under Hookes law its stiffness is measured by Young’s modulus of elasticity. The higher is the value of Young’s modulus, the stiffer is the material in tensile and compressive stress. It is called the modulus of stiffness or modulus of elasticity in shear. The modulus of rigidity is usually 40% of the value of young’s modulus for commonly used materials in volumetric distortion the bulk modulus.

     

    8) HARDNESS: Hardness is defined as the ability of a metal to cut another metal.

    A harder metal can always cut output impression to the softer metals due to its hardness

    It is a very important property of metals and has a wide variety of meanings it embraces many different properties such as resistance to wear, resistance to indentation, resistance to scratches, resistance to deformation and machine mobility, etc.  Diamond is the hardest known material naturally.

    9) CREEP: When a metal part is subjected to high constant stress at a high temperature for a longer period of time it will undergo a slow and permanent deformation which is known as creep. If the material will be continuously subjected to high stresses at higher temperature crack can be formed which may further propagate towards failure called creep failure.

     

    10) FATIGUE: Fatigue is the failure of a material due to cyclic or repeated loading. The intensity of the load may be very less than the ultimate tensile stress, but due to the repeated or cyclic action of the load, the crack initiates and propagates which leads to the fatigue failure.

    The fatigue process leads to Macroscopic and microscopic discontinuities (at the crystalline grain scale) as well as component design features that cause stress concentrations (holes, keyways, sharp changes of load direction, etc.) are common locations.

     

    11) RESILIENCE: It is the amount of energy which a body can absorb without permanent deformation.

     

    12) TOUGHNESS: The amount of energy that a material can absorb without breaking is called the toughness of that material. In other words, it is the ability of a material to absorb energy and deform plastically without fracturing.

     

    Difference between toughness and resilience:

    On application of external load on any material, in general, the material exiibits elasticity then it reaches the plasticity stage and after plasticity the material fails or breaks. Toughness is the energy absorbed without fracture of the material (i.e. the energy absorbed during elastic stage + the energy absorbed during the plastic stage before failure). However, Resilience is the energy absorbed during the elastic stage only i.e. the energy absorbed without permanent deformation of the material.

     

    13) WELDABILITY: Weldability is not a main mechanical property, but it is very important when the material needs to be welded. Weldability is the ability of a material to be welded and retain its properties after the welding. If a material can be welded very easily with other materials, in any position, and able to retain the specified properties then we can say that the weldability of that material is good.

    Carbon equivalent plays a very crucial role in determining the weldability of steel. In general, A material with a carbon equivalent less than 04% is considered as good weldability, Any material with a carbon equivalent between 0.4% to 0.5% is considered as limited weldability material and any material having a carbon equivalent of more than 0.5% is considered as poor weldability material. This is summarised below

    • Up to 0.4%: Good Weldability
    • Between 0.4 to 0.5%: Limited Weldability
    • Above 0.5%: Poor Weldability

     

    Please watch the below video to understand more about the mechanical properties of the materials:

     

    References and for further reading;

    1. Wikipedia: Click here to read

    2. thengineerspost.com

     

    This article is written by:

    MR. ABHISHEK SRIVASTAVA 

    B.TECH (MECHANICAL ENGG.)

    • 4+ Years of Industrial Experience
    • 2+ Years of Teaching

    E-Mail: abhi.allahabad122@gmail.com

  • Knuckle Joints

    Knuckle Joints

    WHAT IS A KNUCKLE JOINT?

    A knuckle joint is a type of mechanical joint used to join two components that are loaded under tensile load. One has a fork with holes on either side, forming a double eye, while the other component has a Single eye. The single eye is inserted between double eyes so that all three holes are centered, and a pin is used to secure these components. These joints are used for different types of connections e.g. tie rods, tension links in bridge structure roof tiles, bridges, and cranes, etc. These joints can easily be assembled and dissatisfied. The ability to allow some rotations can be advantageous in truss structures because it ensures that the structural members remain under a net stress load and are not subject to bending moments, which can increase the stress. Now let’s discuss this more clearly;

     

    • Knuckle joints always have a fork end, an eye end, & a pin. Usually, these are all specially made parts, though the standard rod ends are sometimes used for the ends of the eye.
    • This has the advantage that an end rod performs an additional rotation motion perpendicular to the axis, protecting against bending constraints.
    • The axle can be bolted in case of huge structural materials like bridges, heavy-duty vehicles, etc.
    • A single degree of freedom (1-DOF) kinematics pair is allowed in this joint so this joint is also called as an inverted joint or pin joint allowing only relatives rotation about the single axis. The other two degrees of freedom are seized in it.
    • This is a type of joint that connects two cylindrical rods whose axes lie on the same plane and under tensile loads. It is used to transmit axial tensile force. This joint allows the angular movement of two cylindrical rods in one plane.

    PARTS OF A KNUCKLE JOINT:

    • Eye part
    • Double Eye End or Fork End.
    • Two rods are to be connected
    • Knuckle Pin.
    • Collar.
    • Tapers Pin or Lock Pin

     

    Different parts of a knuckle joint shown in the below figure;

    Parts of a knuckle joint

     

     

    The Assembly of different parts of a knuckle joint is shown in the below figure;

    assembly of a knuckle joint

     

     

    CONSTRUCTION AND FUNCTIONS OF DIFFERENT PARTS:

    The arrangement as shown in the above figures has an eye fork end & one eye end. The collar, taper pin & Knuckle pin provides an axial arrangement to these joints. The end of one eye is placed between two eye ends or two eyes of a fork. After that, a nozzle pin is inserted at the end of the eye and the end of the fork. The fork pin is used to hold the fork end and eye end together.

    Some part of the knuckle pin comes outside of the lowermost hole of the fork end.

    There is a small hole under the knuckle pin, at the ends of the eye, and fork Collar and tamper pins are used to lock the knock pins.

    The collar is placed in such a way that the holes of the knuckles are attached to the collar hole, and a taper pin is inserted from the collar hole into the collar hole having two pinholes.

    This simplifies the formation of the Knuckle joint, some parts of the knuckle pin comes outside of the lowermost hole of the fork end.

     

    FAILURE OF DIFFERENT PARTS IN A KNUCKLE JOINT:

    Types of failures that can occur in knuckle joints are;

    1. Tensile failure of Flat Ends
    2. Tensile failure of Solid Rod
    3. Failure of Single Eye End & Shears Pin Hole
    4. Pin crushed against the rod
    5. Shear failure of Knuckle Pin
    6. Tensile failure of Double Eye End

     

    DESIGN OF KNUCKLE JOINT:

    DESIGN OF KNUCKLE JOINT:

     

    Material selection: The material selected is low carbon steel, which can withstand the stresses developed in the material, as the joint is subjected to reversible stress, then the induced stress will be repeated, and the joint may fail due to fatigue.C-30 is selected as the material for all parts

     

    The assembly diagram of the knuckle joint is as shown in the above figure.

    The dimensions of knuckle joints are:

    • Diameter of rod = d
    • Diameter of knuckle pin = dp    = d1
    • Outside diameter of single eye = doe = d2
    • Outside diameter of double eye = dod
    • Thickness of single eye = t
    • Thickness of fork = t1
    • Axial tensile force on rod = P

     

    (1) Diameter of rod

    Consider the rod is subjected to a direct tensile stress

        ς(Zeta) = P / π d2  

    From the above equation, the diameter of the rod ‘d’ is obtained.

     

    (2) Design of pin (dp)

     

    (a) Consider the failure of the pin under double shear due to tensile force.

    Therefore, direct shear stress induced in knuckle pin is given by Equation

    ς(zeta) = P / 2A = (P/2) / (π/4) dp2 = 2P / π dp2

     

    (b) Failure of knuckle pin in bending

    Assume there is no clearance or slack but in actuality, knuckle pin is loose in forks to permit angular moment of one with respect to other, so it is subjected to bending moment in addition to shear, consider uniformly distributed load along the portion of the pin.

    Taking moment about axis XX

        M = [(-P/2) × (t/4)] + { (P/2) × [ (t/2)+(t1/3) ] }

         = P/2 [(t1/3)+(t/2)-(t/4) ]

        = P/2 [ (t1/3)+(t/4) ]

    Section modulus,   

    Z = (π/ 32)dp3

    Maximum bending stress, σb

    σb= M/Z = { P/2 [(t1/3)+(t/4)] } / {(π/ 32)dp3}

     

    Here, we check the pin in bending and find the value of dp

     

    (3) Design of single eye :

     

    (a) To find the outside diameter of single eye (doe) The single eye is subjected to a direct tensile stress, due to this single eye under the tear.

    σt = P/A = P/ (doe-dp)× t

     

    (b) Due to direct tensile strength, the single eye is subjected to double shear.

     Resisting shearing area = 2(doe-dp)×(t/2)

    The direct shear stress induced is

    ς(Zeta)=P/(doe-dp)×t

    From this equation, the outside diameter of the single eye doe is obtained.

     

    (C) Failure of single eye or pin due to tensile load in crushing

        Resisting crushing area = dp × t

        σc = P/(dp×t)

     From this equation crushing stress checked if fail, increase the thickness of the eye (t).

     

    (4) Design of fork (double eye)

     

    (a) The tearing of the double eye at weakest section due to tension

    Area resisting tear = (dof – dp) × 2 t1

          σt =    p/ [(dof – dp) × 2 t1]

    From this equation, find the outside diameter of the fork (dof).

     

    (b) Failure of the double eye (fork) in double shear due to tensile load.

    Area resisting shear  = 4 × [(dof – dp) ]/2 × t1

        = 2 × (dof – dp) t1

    The shear stress is given by,

        ς(zeta) = p/[(dof – dp) × 2 t1]

     

    From this equation, check shear stress if less than design, increase the thickness of fork t1.

     

    (c) Failure double eye in crushing (thickness of fork)

    Double eye may fail in crushing due to tensile load

    The crushing stress is given by,

        σc = P/( 2×dp ×t1)

    Check crushing stress or find t1

     

    Application of Knuckle Joint:

    The following are the main points of knuckle joint applications:-

    • Link of roller chains, bicycle chains, and watch chain straps.
    • The valve mechanism of a reciprocating engine.
    • The fulcrum for the lever.
    • Link of roller chains, bicycle chains, and watch chain straps.
    • The joint between the tie rod joints of a roof truss.
    • In an automobile, a finger wheel is supporting the skeleton for assembly.
    • Tie rod joint of the jib crane.
    • The knuckle joint is also used in wheel alignment parts of tractors.
    • This eccentric flush work on some occasions uses a downward string such as barrel steps, lateral drilling, etc.
    • It is also used in robotic arms or earthmovers such as grains or tanks.
    • Knuckle joints are mainly used for combining in rail compartments.
    • It is used in the vehicle’s windshield wipers.

     

    Advantages of Knuckle Joint:

    Followings are the main advantages of knuckle joints:-

    • The Knuckle joint withstands high tensile loadings, less expensive, and more reliable.
    • Strong mechanical rigidity.
    • It can be easily assembled and disintegrated.
    • High repetition accuracy even with material thickness and tensile strength & Long tool life.
    • This leads to high system rigidity.

     

    Disadvantages of Knuckle Joints:

    Followings are the main disadvantages of knuckle joints:-:-

    • Unable to withstand large compressive loads.
    • It is not as flexible as a universal joint.
    • Angular movement is constrained to only one plane.

     

    REFERENCES:

    1. R.S. Khurmi, J.K. Gupta. A textbook of machine design. Ram Nagar, New Delhi: Eurasia Publishing House. ISBN 81-219-2537-1 (2008). 

    2. Analysis of Knuckle Joint of 30C8 Steel for Automobile Application -Sourav Das, Vishvendra Bartaria, Prashant Pandey: International Journal of Engineering Research & Technology (IJERT) Vol. 3 Issue 1, January – 2014 

    3. Bhandari, V.B. (2001). Introduction to machine design. New Delhi: Tata McGraw-Hill. 2001

    4. Material Optimization for Knuckle Joint by Using FEA Somase Anil R1, Dhole Sumit M2, International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 06 Issue: 10 | Oct 2019 www.irjet.net

    5. https://fastenerengineering.com/what-is-a-knuckle-joint/ By Michelle Froese

     

    This article is written by:

    MR. ABHISHEK SRIVASTAVA 

    B.TECH (MECHANICAL ENGG.)

    • 4+ Years of Industrial Experience
    • 2+ Years of Teaching

    E-Mail: abhi.allahabad122@gmail.com

  • Glossary of Valve Terms

    Glossary of Valve Terms

    The commonly used terms and definitions related to valves is given below;

    Actual pressure drop: The difference between the inlet pressure and the outlet pressure of a valve.

    Actuator: A device used to open/close or control the valve. Key types include electrical, hydraulic, and pneumatic. Movement may be quarter-turn or multi-turn.

    Actuator stem: A rod used in linear designed valves connecting the actuator with the stem of the valve.

    Back seat: In linear valves, the area of the stem that enters the valve bonnet is sealed to prevent process fluid from entering the packing box and to prevent deterioration of the sealing materials.

    Ball valve: A quarter-turn valve with a spherical closing element held between two seats. Characteristics include quick opening and good shutoff.

    ====================
    ====================

    Bellows: A sealing device that prevents line media from leaking between the stem and the body.

    Blowdown: The discharge of process fluid to reduce the pressure in a piping system. This is usually done through a pressure relief device.

    Breakout torque: The torque required to open or unseat a rotary valve.

    Bubble-tight: When there is no measurable seat leakage over a certain period of time during test conditions.

    Butterfly valve: A quarter-turn valve, which has a circular disc as its closing element. The standard design has the valve stem running through the center of the disc, giving a symmetrical appearance. Later more complex designs offset the stem so that the disc “cams” into the valve seat.

    Bypass valve: A valve smaller in diameter that is fitted in parallel to a larger main valve. Bypass valves are used to reduce the differential pressure across the main valve before this main valve is opened (as otherwise this larger, more expensive valve, may suffer damage to internal components).

    Check valve: A valve that is designed to allow the fluid to flow in a given direction but closes to prevent back flow. Types include swing check, tilting-disc check, and wafer check, non-slam (piston type).

    Class: The class is used to describe the pressure rating of the piping system. For example, Class 150 lb, 300 lb, 600 lb, 900 lb, or API 3000, API 5000. This relates to the maximum allowable design pressure that a flange of certain dimensions and made of a certain material can be used within a piping system.

    Concentric butterfly valve: A butterfly valve with the disc installed in the center of the valve.

    Control valve: A valve that regulates the flow or pressure of a fluid. Control valves normally respond to signals generated by independent devices such as flow meters or temperature gauges. Control valves are normally fitted with actuators and positioners. Pneumatically actuated globe valves are widely used for control purposes in many industries, although quarter-turn types such as (modified) ball and butterfly valves may also be used.

    Cryogenic valves: Valves suited for use at temperatures below 45 degrees Celsius. A cryogenic valve should have a cold box as an integral part of the body to allow a vapor barrier to form between the packing box and the liquified gas.

    Cv: The Cv of a valve is defined as 1 U.S. gallon of 60°F water for 1 minute with a 1 psi pressure drop. Also known as the valve coefficient or the flow coefficient.

    Diaphragm valve: A bi-directional valve that is operated by applying an external force to a flexible element or a diaphragm (typically an elastomer). Diaphragm valves may be used for slurries (where other valve designs might clog) or in hygienic applications.

    Direct-acting actuator: A diaphragm actuator that allows the actuator stem to extend.

    Double-acting positioner: A positioner that has the facility to supply and exhaust air on both sides of the actuator piston or diaphragm at the same time.

    Double block and bleed: A valve configuration in which positive shutoff is achieved at both the inlet and outlet sides. A small port is fitted to discharge fluid in the intermediate space. Fitting a gas detector to the port assures the integrity of the upstream seal. This configuration is often required to isolate high-pressure sections of a system to facilitate safe maintenance, etc.

    Double disc check valve: A check valve with two semi-circular discs that are hinged together and that fold together when the flow is in the correct direction and swing closed when the flow is reversed. Also known as a split disc check valve.

    Drop tight: A bubble-tight test that involves a water-under-air test.

    Eccentric butterfly valve: A butterfly valve where the shaft that carries the closure disc is slightly offset and creates an elliptical motion as it leaves the sealing surface. This effect reduces friction and wear to the closure disc.

    Elastomer: A polymer that is both flexible and resilient when used as a seal.

    End to end: The extremities of the valve. One connection to the other end connection.

    Extended bonnet: Used when the medium is at high or low temperatures, to avoid damage to the sealing elements.

    Fail closed: An actuator facility such that in the event of power failure the valve will move to a fully closed position.

    Fail open: An actuator facility such that in the event of power failure the valve will move to the fully open position.

    Fail-safe: An actuator facility such that in the event of power failure the valve will move to a predetermined position, which could be open, closed, or an intermediate position.

    Fire-resistant: The ability of a valve to withstand a fire and maintain the failure position. Such a valve will be equipped with devices to achieve this status.

    Fire-safe: The ability of a valve to minimize the amount of process lost downstream or to the atmosphere after a fire test.

    Flat face:  flange that has no raised face or a ring groove surface. These flanges are generally used in lower piping pressure classes such as ASME 125 lb or 150 lb in cast iron and carbon steel. The mating gasket will be flat and extend to the circumference with holes to accommodate the flange bolting.

    Flat gasket: A circular, flat sheet with an inside and outside diameter.

    Floating ball: A ball valve where the closure ball is not attached to the body of the valve.

    Floating seat: A seat ring that is not attached to the valve body and can move to suit the closure element and improve the shut-off.

    Float valve: A valve that automatically opens or closes as the level of liquid changes. The valve is operated mechanically by a float that rests on the top of the liquid.

    Full-bore valve: Any valve where the closure element has the same inside diameter as the inlet and outlet of the valve. Also called a full-port valve and has a lower pressure drop than a reduced bore.

    Full closed: The position of the valve when the closure element is fully seated.

    Full open: The position of the valve when the closure element is fully open allowing maximum flow through the valve.

    Full trim: The area of the valve’s seat that can pass the maximum flow for that particular size.

    Galling: The damage of two mating parts when microscopic portions impact and make a temporary bond. When effort is made to separate these two surfaces, tearing of the two components can occur. This usually happens when the two materials are the same or possess several very similar mechanical characteristics.

    Gate valve: A multi-turn valve that has a gate-like disc and two seats to close the valve. The gate moves linearly, perpendicular to the direction of flow. This type of valve is normally used in the fully opened or fully closed position; it is not suited to throttling applications. Gate valves provide robust sealing and are used extensively in the petrochemical industries. This class of valve also includes knife gate valves, conduit gate valves, and wedge gate valves.

    Gland bushing or the packing follower: Located at the top of the packing box, it acts as a barrier, protects the packing from the atmosphere, and transfers a force from the gland flange bolting to the packing.

    Gland flange: Part of the valve used to compress and retain the internals in the packing box.

    Globe valve: A multi-turn valve with a closing element that moves perpendicularly to the valve body seat and generally seals in a plane parallel to the direction of flow. This type of valve is suited to both throttling and general flow control.

    High-performance valves: A valve specifically designed for accurate throttling applications.

    Hydrostatic test: A test using water under pressure to detect any leaks through the body, sealing joints, or closure element. Generally, this test pressure is 1.5 times the design pressure at ambient temperature.

    Integral flange: A flanged connection that is either fabricated or cast to the body of the valve.

    Integral seat: A seat that is actually a machined part of the valve body and not one that is inserted into the valve.

    Jacketed valve: Valve designed to incorporate a so-called jacket around the valve body. Steam is introduced into the jacket to keep the fluids being controlled at the required temperature.

    Lift check valve: A non-return valve that prevents back flow by having a free floating element, either a ball or a poppet. The design incorporates a piston to damp the disc during operation.

    Limit stop: A device in an actuator that limits the linear or rotary motion of an actuator; can be adjusted.

    Limit switch: An electromechanical accessory that is attached to an actuator and used to identify the position of a valve’s closure element.

    Linear valve: A valve that has a sliding stem that pushes the throttling element up and down.

    Line blind: A pipeline shut-off device, whereby a flat disc is forced between two flanges. Line blinds are less expensive than valves, but require much more time to operate.

    Lug body: A body of a flangeless wafer butterfly valve that requires bolts to pass through the body to flanges on either side of the valve. These holes can be tapped to allow the line to be dismantled without “dropping” the valve. Tapped lugged valves are sometimes called “end of line” valves.

    Multi-ported:  These valves include additional inlet/outlet ports, to allow fluids to be directed. The ball and plug valve types are ideally suited to multiport designs.

    Multi-turn: Category of valves (such as gate, globe, needle), which require multiple turns of the stem to move the valve from the fully open to the fully closed position. Also known as linear valves.

    National pipe thread: A tapered thread that is used for pressure connections for piping.

    Needle valve: Multi-turn valve that derives its name from the needle-shaped closing element. The design resembles that of the globe valve. Typically available in smaller sizes, they are often used on secondary systems for on/off applications, sampling, etc.

    Non-rising stem: A valve where the stem is threaded and the turning of a stationary operator will result in the closure element rising to open and lowering to close.

    Normally closed: A valve that is normally closed during operation. In many cases, these valves are locked closed by using a mechanical device.

    Normally open: A valve that is normally open during operation. In many cases, these valves are locked open by using a mechanical device.

    O-ring: An elastomer ring that forms a sealing material for the internals of a valve.

    Packing: A soft sealing material that is used to prevent leakage of process fluid from around the stem. It is located in the packing box.

    Packing box: A chamber through which the stem passes. This chamber houses the packing material, packing spacers, lantern rings, guides, and other seal accessories necessary to prevent leakage of process fluid.

    Parallel gate valve: A gate valve that has a flat disc gate that slides between two parallel free floating seats.

    PEEK: The abbreviation for polyether ether ketone. A robust soft seating material.

    Pilot valve: Small valve requiring little power that is used to operate a larger valve.

    Pinch valve: A valve in which a flexible hose is pinched between one or two moving external elements to stop the flow. This valve is often used in slurry and mining applications, as its operation is not affected by solid matter in the medium. It is also used with certain gases, as the absence of possible leak paths to the atmosphere ensures good emission control.

    Plug valve: This multi-turn valve derives its name from the rotating plug that forms the closing element. The plug may be cylindrical or truncated. In the open position, the fluid flows through a hole in the plug. Lubricated plug valves rely on a sealing compound injected between the plug and the valve body, whilst sleeved plug valves are fitted with a “soft” insert between the plug and the body.

    Poppet: A closure element in a check valve that is held in place by a spring.

    Positioner: A device that receives a signal—pneumatic or electric – from a controller and compares it to the actual position of the valve. If the signal is not correct then the positioner sends pressure to, or bleeds pressure from, the valve so that the correct position is achieved.

    Proximity switch: A limit switch that indicates the valve position without making mechanical contact. The switch will use a magnetic or an electronic sensor to determine the valve position.

    Psi: The abbreviation for pounds per square inch.

    psia: The abbreviation for pounds per square inch absolute. The psia unit is used when the pressure is expressed without taking into account ambient pressure.

    Psig: The abbreviation for pounds per square inch gauge. The psig unit is used when the pressure is expressed to standard atmospheric pressure (noted 14.7 psia).

    Quarter-turn: The 90◦ angle through which a valve’s closing element must move from the fully open position to the fully closed position. Examples are ball, plug, and butterfly valves.

    Rack and pinion actuator: An actuator used in conjunction with quarter-turn valves. This actuator will supply either a pneumatic or a hydraulic force to move a flat-toothed rack that turns a gear to open and close the closure element.

    Reduced-port valve: A valve that has a smaller internal bore than those of the inlet and the outlet. A reduced-port (bore) ball valve will have a greater pressure drop than a full-port (bore) ball valve.

    Ring type joint: A flanged end connection with a circular groove on the mating face, where a softer metal ring is placed before mating up to a similar flange face and bolting up. The softer ring, usually oval or hexagonal, will deform when the flanges are bolted up and create a tight seal. Ring type joint connections are used on higher-pressure piping systems, ASME 900 lb and above. The abbreviation is RTJ.

    Screwed bonnet: A valve bonnet with male threads to join a valve body with female threads.

    Screwed end connections: End connections that have female national pipe thread (NPT), which mates with male NPT on a pipe.

    Seating Torque: The torque value produced by a rotary actuator to open or close the valve.

    Shaft: The rod that connects the closure element and the closure operator (handwheel or actuator).

    Single-acting actuator: An actuator in which air is applied to one chamber. This air pressure acts against and pushes a plate.

    Sliding gate valve: A gate valve that has a flat rectangular plate as a closure element. Sometimes called a sluice valve and used for large bore irrigation and waterworks systems.

    Soft seat plug: An elastomer that is placed within a metal ring at the seating area of a globe valve. This will provide a bubble-tight shut-off.

    Speed of response: The speed provided by an actuator to operate a valve. Sometimes called the stroking speed.

    Split body: Usually refers to a ball valve that comprises more than one piece and houses the closure element.

    Stroke: The travel required by a valve, either linear type or rotary type, generally from fully open to fully closed.

    Sub-sea valve: A valve that is designed for use in seawater. For example, installed in a pipeline on the seabed.

    Swing check valve: A check valve with a single plate pivoted at the top and secured to the body of the valve. The flow of the process fluid pushes the plate open and in the event of flow reversal the plate swings to the closed position.

    Tank valve: A valve arranged for fitting at the bottom of a tank or process vessel.

    Three-way valve: A diverter type valve that has three ports and allows the flow path of the process fluid to be switched, or two different flow paths to be combined.

    Throttling: The regulation of the process fluid by positioning the closure element of the valve between open and closed to create the desire flow regime.

    Through-conduit gate valve: A full-bore gate valve that has a very low-pressure drop and allows for the passage of pipeline pigs or scrapers for cleaning, de-watering, batching, etc.

    Thrust: The force generated by any type of actuator to open, close, or position the closure element of a valve.

    Trim: The trim of the valve is the parts of the closure element that are exposed to the process flow, sometimes called the wetted parts.

    Trunnion mounted ball valve: A robust ball valve, where the closure element ball is supported at the base by a shaft. This design is more common on larger valves and higher ratings, because of the weight of the ball.

    V-ring packing: A stem packing that is V-shaped in cross-section. Radial forces that are applied will force out the packing radially and create a tight seal against the wall of the packing box and the stem/shaft.

    Wafer design: The construction of wafer design valves allows them to be “sandwiched” between flanged sections of the pipeline. The benefit is lower bolting requirements. Typically used with certain butterfly and check valves.

    Water hammer effect: The reaction when a valve is suddenly closed and a shock wave is transmitted through the piping system. This is generally caused by the under-sizing of the piping system. It is not only noise, but it can also cause mechanical damage to the piping system and associated equipment.

    Weir: An obstruction in a diaphragm valve, against which the elastomer liner is compressed to prevent the flow of the process fluid.

    Wellhead Valve: Used to isolate the flow of oil or gas at the take-off from an oil or gas well. The design is usually a plug or gate valve.

     

    To read about the Butterfly Valves, Please click here

    To read about the Ball Valve, Please click here

    To read about the Plug Valves, Please click here

    To read about the Gate Valves, Please click here

    To read about the Globe Valves, Please click here

    To read about the Safety Valves, Please click here

    To read about the Valve Basics, Please click here

     

    This article is written by

    Mr. Goutham Rathinam

    (BE-Mechanical & CSWIP 3.1-TWI, UK)             

    Email ID: goutham.r86@gmail.com

  • Pressure Safety Valve – What is a Valve (Part – 6)

    Pressure Safety Valve – What is a Valve (Part – 6)

    Pressure safety valve PSV

    Pressure Safety Valve / Relief Valve

    A safety valve is a valve that acts as a protection of equipment from exploding or damaging and it is mainly installed in pressure vessels such as chemical plants, electric power boilers, and gas storage tanks.

    Safety Relief Valve is a type of valve that automatically actuates when the pressure of inlet side of the valve increases to a predetermined pressure, to open the valve disc and discharge the fluid (steam or gas); and when the pressure decreases to the prescribed value, to close the valve disc again.

    Reasons for excess pressure in a vessel:

    There are a number of reasons why the pressure in a vessel or equipment can exceed a predetermined limit. The most common are: Blocked outlet; Exposure to external fire, often referred to as “Fire Case”; Thermal expansion of fluid; Abnormal process conditions (Chemical reaction); Cooling system failure; Heat exchanger tube rupture; Pipework component failure; Control Valve failure, etc.

    Each of the above-listed events may occur individually or simultaneously. Every cause of over-pressure will create a different mass or volume flow to be discharged. For e.g. small mass flow for thermal expansion and large mass flow in case of a chemical reaction. It is the process engineer’s responsibility to determine the most worst-case scenario for the sizing and selection of a suitable pressure safety device.

    pressure safet valve parts

    What is the difference between Relief Valve and Safety Valve?

    Relief valve: A spring-loaded pressure-relief valve actuated by the static pressure upstream of the valve. The valve opens normally in proportion to the pressure increase over the opening pressure. A relief valve is used primarily with incompressible fluids such as any Liquid.

    Safety valve: A spring-loaded pressure-relief valve actuated by the static pressure upstream of the valve and characterized by rapid opening or pop action. A safety valve is normally used with compressible fluids such as any Gases, Steam.

    Safety Valve Types

    The terms full lift, high lift, and low lift refer to the amount of travel the disc undergoes as it moves from its closed position to the position required to produce the certified discharge capacity, and how this affects the discharge capacity of the valve.

    Full-Lift Safety Valve:

    A full lift safety valve is one in which the disc lifts sufficiently so that the curtain area no longer influences the discharge area. The discharge area, and therefore the capacity of the valve are subsequently determined by the bore area. This occurs when the disc lifts a distance of at least a quarter of the bore diameter. A full lift conventional safety valve is often the best choice for general steam applications.

    FULL LIFT RELIEF VALVE

    High-Lift Safety Valve:

    The disc of a high lift safety valve lifts a distance of at least 1/12th of the bore diameter. This means that the curtain area, and ultimately the position of the disc, determines the discharge area. The discharge capacities of high lift valves tend to be significantly lower than those of full lift valves, and for a given discharge capacity, it is usually possible to select a full lift valve that has a nominal size several times smaller than a corresponding high lift valve, which usually incurs cost advantages. Furthermore, high lift valves tend to be used on compressible fluids where their action is more proportional.

    Low-Lift Safety Valve:

    In low lift valves, the disc only lifts a distance of 1/24th of the bore diameter. The discharge area is determined entirely by the position of the disc, and since the disc only lifts a small amount, the capacities tend to be much lower than those of full or high lift valves.

    Relief Valve Types

    Conventional Safety Relief Valve:

    A conventional safety Relief Valve is a pressure Relief Valve which has its spring housing vented to the discharge side of the Valve. The operational characteristics (opening pressure, closing pressure, and relieving capacity) are directly affected by changes of the back pressure on the Valve.

    Conventional Safety Relief Valve

    Balanced Safety Relief Valve:

    A balanced safety Relief Valve is a pressure Relief Valve which incorporates means of minimizing the effect of back pressure on the operational characteristics (opening pressure, closing pressure, and relieving capacity).

    Pilot-Operated Pressure Relief Valve:

    A pilot-operated pressure Relief Valve is a pressure Relief Valve in which the major relieving device is combined with and is controlled by a self-actuated auxiliary pressure Relief Valve.

    Power-Actuated Pressure Relief Valve:

    A power-actuated pressure Relief Valve is a pressure Relief Valve in which the major relieving device is combined with and controlled by a device requiring an external source of energy.

    Temperature-Actuated Pressure Relief Valve:

    A temperature-actuated pressure Relief Valve is a pressure Relief Valve that may be actuated by external or internal temperature or by pressure on the inlet side.

    Temperature-Actuated Pressure Relief Valve

    Vacuum Relief Valve:

    A vacuum Relief Valve is a pressure relief device designed to admit fluid to prevent an excessive internal vacuum; it is designed to reclose and prevent further flow of fluid after normal conditions have been restored.

    Terminology

    Accumulation: The pressure increases over the MAWP of the vessel, expressed in pressure units, or as a percentage of MAWP or design pressure. Maximum allowable accumulations are established by applicable codes for emergency operating and fire contingencies.

    Actual discharge area or actual orifice area: The area of a pressure-relief valve (PRV) is the minimum net area that determines the flow through a valve.

    Backpressure: The pressure that exists at the outlet of a pressure-relief device as a result of the pressure in the discharge system. Backpressure is the sum of the superimposed and built-up backpressures.

    Superimposed backpressure: The static pressure that exists at the outlet of a pressure-relief device at the time the device is required to operate. Superimposed backpressure is the result of pressure in the discharge system coming from other sources and may be constant or variable.

    Built-up backpressure: The increase in pressure at the outlet of a pressure-relief device that develops as a result of flow after the pressure-relief device opens.

    Blowdown: The difference between the set pressure and the closing pressure of a pressure-relief valve, expressed as a percentage of the set pressure or in pressure units.

    Bore area/nozzle area/nozzle throat area/throat area: The minimum cross-sectional flow area of a nozzle in a pressure-relief valve.

    Closing pressure: The value of decreasing inlet static pressure at which the valve disc re-establishes contact with the seat or at which lift becomes zero as determined by seeing, feeling, or hearing.

    Cold differential test pressure (CDTP): The pressure at which a pressure-relief valve is adjusted to open on the test stand. The CDTP includes corrections for the service conditions of backpressure or temperature or both.

    Curtain area: The area of the cylindrical or conical discharge opening between the seating surfaces above the nozzle seat created by the lift of the disc.

    Opening pressure: The value of increasing inlet static pressure at which there is a measurable lift of the disc or at which discharge of the fluid becomes continuous, as determined by seeing, feeling, or hearing.

    Operating ratio of a pressure-relief valve: The ratio of maximum system operating pressure to the set pressure.

    Overpressure: The pressure increases over the set pressure of the relieving device. Overpressure is expressed in pressure units or as a percentage of set pressure. Overpressure is the same as accumulation only when the relieving device is set to open at the MAWP of the vessel.

    Set pressure: The inlet gauge pressure at which the pressure-relief device is set to open under service conditions.

    Pressure-relief device (PRD): A device actuated by inlet static pressure and designed to open during an emergency or abnormal conditions to prevent a rise of internal fluid pressure in excess of specified design value. The device also may be designed to prevent an excessive internal vacuum. The device may be a pressure-relief valve, a non-reclosing pressure-relief device, or a vacuum relief valve.

    Conventional pressure-relief valve: A spring-loaded pressure-relief valve whose operational characteristics are directly affected by changes in the backpressure.

    Balanced pressure-relief valve: A spring-loaded pressure-relief valve that incorporates a bellows or other means for minimizing the effect of backpressure on the operational characteristics of the valve.

    Modulating pressure-relief valve: A pressure-relief valve that opens and flows in proportion to the inlet pressure for some or all parts of the valve’s operating range from set pressure to overpressure at full lift.

    Pilot-operated pressure-relief valve: A pressure-relief valve in which the major relieving device or main valve is combined with and controlled by a self-actuated auxiliary pressure-relief valve (pilot).

    Non-reclosing pressure-relief device: A pressure-relief device that remains open after operation. A manual resetting means may be provided.

     

    This article is written by

    Mr. Goutham Rathinam

    (BE-Mechanical & CSWIP 3.1-TWI,UK)             

    Email ID: goutham.r86@gmail.com

  • Aluminum and aluminum alloys

    Aluminum and aluminum alloys

    Introduction:

    Aluminum is found on the earth in its oxidized form known as Bauxite. Bauxite is refined to produce Alumina (Aluminium Oxide – Al2O3). Approximately 40% – 60% Alumina i.e. Aluminium Oxide (Al2O3) can be extracted from Bauxite.

    The Hall-Héroult electrolysis process (invented in 1886) further processes Alumina (Aluminum Oxide-Al2O3) to separate it from oxygen. This process made possible the production of Aluminium on a large scale and significantly reduced the production cost too.

     

    Some of the very important properties of Aluminum that makes it a very lucrative metal are;
    • It is highly resistant to corrosion
    • It is non-toxic
    • Possesses good electrical and thermal conductivity
    • It is nonmagnetic.
    • Retains good ductility at sub-zero temperatures

     

    Aluminum and aluminum alloys are very suitable for critical applications such as;
    • Space, aircraft, and marine industries
    • Vessels and storage tanks
    • Automotive industries
    • Structural applications and many such consumer products.

    [NOTE: ‘Aluminum’ and ‘Aluminium’ are essentially the same. The word ‘Aluminium’ is very popular in Non-American English.]

     

    Melting point of Aluminium:

    The melting point of pure Aluminum is 660°C (1220°F).  However, the melting point of the Aluminum alloys varies from  480°C to 660°C (900°F to 1220°F), depending on the alloying element.

     

    Density of Aluminium:

    The density of aluminum is;

    • 2.7 g/cm³ (2,710 kg/m³) 
    • 168.56 lbs/ft³ (0.0975 lbs/in³)

     

    Major alloying elements (with Aluminium):

    Major alloying elements are copper, manganese, silicon, magnesium, and Zinc, etc.

    Aluminum alloys are identified by a 4 digit number. The first digit represents the major alloying element, please see the table below;

     

    aluminium designation identification

     

    As explained above, the first digit represents the major alloying elements. However, the last three digits represent the following;

    For 1XXX series (Pure Aluminum group):
    • The second digit indicates a consecutive modification of an original alloy
    • The last two digits indicate the minimum percentage of Aluminium
    For alloys in the 2XXX – 9XXX series (Aluminum with major alloying elements):
    • The second digit indicates a consecutive modification of an original alloy
    • The last two digits have no significance, it only shows that this particular series of metal belongs to the Aluminium alloy group.

     

    1XXX Series:

    • This series is often regarded as the pure aluminum group. These alloys have the following characteristics;
    • The aluminum content shall be more than 99.0% in this group of alloys
    • The ultimate tensile strength for this group of alloys is between 69 MPa to 186 MPa (10 ksi to 27 ksi)
    • They have superior corrosion resistance and hence suitable for specialized chemical tanks and pipings
    • Good electrical conductivity hence suitable for bus bar applications
    • Comparatively poor mechanical properties hence not suitable for structural applications
    • These alloys are not heat treatable
    • They have a very narrow melting range but are weldable
    • Can be welded with a matching filler metal (1XXX series) or with the filler alloys of 4XXX

    Most common alloys in this group are the following;

    • 1060 (99.60% minimum aluminum) – Used in chemical process equipment, tanks, and piping.
    • 1100 (99.00% minimum aluminum) – Used in architectural and decorative applications, furniture, deep drawn parts, etc.
    • 1350 (99.50% minimum aluminum) – Used in electrical conductor wire, bus, and cable

     

    2XXX Series:

    The major Alloying element in this group of materials is copper along with aluminum, also called as Aluminium-Copper (Al-Cu) group.

    • The amount of copper varies from 0.7% to 6.8%. These alloys have the following characteristics;
    • Possesses high strength over a wide range of temperatures hence suitable for aerospace and aircraft applications
    • Some of the alloys in the 2XXX series are not considered weldable by arc welding processes because of their susceptibility to hot cracking and stress-corrosion cracking; however, other alloys in this series can be welded by arc processes.
    • These alloys are heat treatable
    • Can be welded with a matching filler metal (High strength filler of 2XXX series) or with the filler alloys of 4XXX series, which contain silicon (Si) or silicon and copper.

    Most common alloys in this group are the following;

    • 2014 – Used in structures, structural and hydraulic fittings, hardware, and heavy-duty forgings for aircraft or automotive uses.
    • 2017 – Usage similar to 2014 and screw machine parts.
    • 2024 – Used in structural, aircraft sheet construction, truck wheel and used for cladding for good corrosion resistance
    • 2036 – Used in the automotive body sheet.
    • 2090 – Used in Structural work, high strength, and damage tolerant aerospace applications.
    • 2218 – Used in pistons, engine cylinders, forging alloy and parts which require good strength and hardness at a higher temperature.
    • 2219 – Used in structural work, aerospace tanks

     

    3XXX Series:

    The major Alloying element in this group of materials is manganese along with aluminum, also called as aluminium-manganese (Al-Mn) alloys group.

    • The amount of manganese ranges from 0.05% to 1.8%. These alloys have the following characteristics;
    • The ultimate tensile strength for this group of alloys is between 110 MPa to 283 MPa (16 ksi to 41 ksi).
    • These alloys are not heat treatable
    • Moderate strength, good corrosion resistance, excellent formability, suitable for use at elevated temperatures hence used for manufacturing of heat exchangers.
    • Due to moderate, not suitable for structural applications
    • Can be welded with filler alloys from the 1XXX, 4XXX, and 5XXX series, depending on their chemical compositions

    Most common alloys in this group are the following;

    • 3003 – Used in Process and food handling equipment, chemical, and petroleum drums and tanks, and general-purpose applications where slightly higher strength than 1100 is required.
    • 3004 – Used in sheet metal which requires higher strength than 3003.

     

    4XXX Series:

    The major Alloying element in this group of materials is silicon along with aluminum, also called as aluminum-silicon (Al-Si) alloys group.

    The amount of silicon varies from 0.6% to 21.5%. These alloys have the following characteristics;

    • The ultimate tensile strength for this group of alloys is between 172 MPa to 379 MPa (25 ksi to 55 ksi)
    • This series of alloys are mainly used as filler metals for both fusion welding and brazing

     

    5XXX Series:

    The major Alloying element in this group of materials is magnesium along with aluminum, also called as aluminum-magnesium (Al-Mg) alloys group.

    • The amount of magnesium varies from 0.2% to 6.2%. These alloys have the following characteristics.
    • The ultimate tensile strength for this group of alloys is between 124 MPa to 352 MPa (18 ksi to 51 ksi)
    • They have the highest strength among the not heat treatable alloys
    • This series of alloys have good weldability
    • These alloys are used in a wide variety of structural applications, such as components of ships, vehicles, bridges and pressure vessels, etc.

    Most common alloys in this group are the following;

    • 5005 – Used in the electrical conductor and architectural applications
    • 5050 – Similar to 3003 and 5005 but stronger. Good finishing qualities
    • 5052, 5652 – Used in Sheet metal applications that require higher strength than 5050. Good corrosion resistance, Storage tanks, boats, appliances.
    • 5083 – Used in cryogenics structures, unfired pressure vessels, marine components, tanks, railroad cars, drilling rigs.
    • 5086 – Used in marine components, tanks, tankers, truck frames.
    • 5154, 5254 – Used in unfired pressure vessels and tankers
    • 5454 – Used in structural applications and tanks for sustained high-temperature service
    • 5456 – Used in structures, tanks, unfired pressure vessels, marine components

     

    6XXX Series:

    Major Alloying element in this group of materials is magnesium and silicone along with aluminum, also called as Aluminium-Magnesium-silicon (Al-Mg-Si) alloys group.

    • The amount of magnesium and silicone is around 1.0%. These alloys have the following characteristics.
    • These alloys are heat treatable
    • The ultimate tensile strength for this group of alloys is between 124 MPa to 400 MPa (18 ksi to 58 ksi).
    • These alloys can be welded with filler metals from the 4XXX and 5XXX series

    Most common alloys in this group are the following;

    • 6009 – Used in the automotive body sheet
    • 6010 – Used in the automotive body sheet
    • 6013 – Used in general structural applications, it has improved strength over 6061
    • 6061 – Used in structural work, architectural, automobile, railway, and marine applications, pipe, and pipe fittings. This alloy possesses good strength, corrosion resistance, good formability, and good weldability
    • 6063 – Used in Pipe, railings, hardware, and architectural applications
    • 6070 – Used in structural applications and piping
    • 6101 – Used for electrical conductors
    • 6262 – Used for Screw machine products and fittings
    • 6351 – Usage similar to 6061
    • 6951 – Used in brazing sheet core alloy

     

    7XXX Series:

    The major Alloying element in this group of materials is zinc along with aluminum, also known as Aluminum-zinc (Al-Zn) alloys group.

    The amount of zinc varies from 0.8% to 12.0%. These alloys have the following characteristics;

    • These alloys are among the highest-strength aluminum alloys and very suitable for high-performance applications, such as aircraft and aerospace components.
    • The common base metals in this series are 7003 and 7005 and can be welded with the 5XXX series filler metal.

    Most common alloys in this group are the following;

    • 7004 – Used in truck trailer and railcar extruded shapes
    • 7005 – Used in truck trailer and railcar extruded shapes
    • 7039 – used in Armor plate
    • 7075 – used in High-strength aircraft and other applications; cladding gives good corrosion resistance
    • 7079 – used in massive parts for aircraft and allied construction
    • 7178 – Used for Aircraft construction, strength slightly higher
  • Butterfly Valves – What is a Valve (Part – 6)

    Butterfly Valves – What is a Valve (Part – 6)

    In the Valves Part-1, we discussed what is a valve, its history, and its categorization (Click here to read).

    In Part-2, we discussed Globe valves (Click here to read).

    In Part-3, we discussed Gate valves (Click here to read).

    In Part-4, we discussed Plug valves (Click here to read).

    In Part-5, we discussed Ball valves (Click here to read).

    In this part, we will learn about Butterfly Valves.

     

    BUTTERFLY VALVES

    Butterfly Valves are quarter-turn rotary valves in which a disc-shaped closure member is rotated through 90 degrees or less to open or close or regulate the flow passage. Butterfly valves may be used for flow in both directions.

    The butterfly valve consists of the following four main components

    • Body
    • Disk
    • Stem
    • Seat

    Body: Butterfly valves generally have bodies that fit between two pipe flanges, the most common being lug and wafer body design.

    Disk: The disk is how the valve stops flow – it is equivalent to a plug in a plug valve, a gate in a gate valve or a ball in a ball valve. There are variations in disk design and orientation in order to improve flow, sealing, and/or operating torque.

    Stem: The stem of the butterfly valve may be a one-piece shaft or a two-piece (split-stem) design. The stem in most resilient seated designs is protected from the media, thus allowing an efficient selection of material with respect to cost and mechanical properties.

    Seat: The seat of a resilient-seat butterfly valve utilizes an interference fit between the disk edge and the seat to provide shutoff. The material of the seat can be made from many different elastomers or polymers. The seat may be bonded to the body or it may be pressed or locked in.

    TYPES OF BUTTERFLY VALVES:

    Efforts to adapt butterfly valves to wider temperature and pressure ranges have led to the development of a family of butterfly valves that may be fitted with seatings of a variety of construction materials to meet the operational requirements. Such seating’s may be metal-to-polymer or metal-to-metal, and may be designed to satisfy the requirements of fire-tested valves. There are different kinds of butterfly valves, each adapted for different pressures and different usage.

    As per Disc Closure Design

    • Concentric Butterfly Valve
    • Eccentric Butterfly Valve

    As per Piping Connection Design

    • Wafer Type Butterfly Valve
    • Lug Type Butterfly Valve
    • Double Flange Butterfly Valve

    Concentric Butterfly Valve

    Concentric Butterfly Valve (Figure 1), also known as Zero Offset Butterfly Valve, is the most basic type of butterfly valve design. The stem passes through the centre-line of the disc which is further placed in the centre of the pipe bore and the seat is the inside diameter periphery of the valve body. The disc is in constant contact with the seat.

    Figure 1

    CONCENTRIC BUTTERFLY VALVE
                                                        CONCENTRIC BUTTERFLY VALVE

    This zero-offset valve design is also called “Resilient Seated” or “Rubber Seated” because it relies on the flexibility of the seat rubber to efficiently seal the flow when closed. Concentric butterfly valves are commonly used for low-pressure ranges. An advantage of concentric butterfly valve is that the media going through the valve will not contact the body since the seat is constructed as a sleeve or cartridge inside of the body.

    Eccentric Butterfly Valve

    In Eccentric Butterfly Valves, also known as High-Performance Butterfly Valves, the stem does not pass through the center-line of the disc but instead located offset from the center according to the categories of double and triple offset valves.

    Difference between Concentric & Eccentric/offset Butterfly Valve (Figure 2)

    Figure 2

    CONCENTRIC VS OFFSET BUTTERFLY VALVE

     

    Single-Offset Butterfly Valve (SOBV):

    When the stem is located right behind the centre-line of the disc, the valve is called Single-Offset Butterfly Valve. This design was developed to reduce the disc contact with the seal before full closure of the valve with the aim of improving service life of the valve. Single-offset butterfly valves have given way to double offset and triple offset butterfly valves.

    Double-Offset Butterfly Valve (DOBV):

    When the stem is located behind the disc with an additional offset to one side. This double eccentricity of the stem enables the rotating disc to rub over the seat for only about one to three degrees.

    1st offset : The axis of the shaft is behind the centre-line of the sealing point of the disc to seat.

    2nd offset : The axis of the shaft is eccentric to the centre of the valve/pipe line.

    Triple-Offset Butterfly Valve (TOV or TOBV):

    It is often used in critical applications and is designed similar to a double offset butterfly valve with one more offset. The third offset is the disc-seat contact axis. The seat surface takes a conical shape which coupled with the same shape at the ridge of the disc, results in minimal contact before full closure of the valve allowing the disc to seal against the seat with no friction. A triple offset butterfly valve is more efficient and allows for less wear. Triple offset butterfly valves are often made of metal seats to create a bubble-tight shut-off. The metal seats allow butterfly valves to be used in higher temperature ranges.

    High performance butterfly valve designs use the pressure in the pipeline to increase the interference between the seat and the disc edge. These butterfly valves have higher pressure ratings and are prone to less wear.

    Figure 3

    BUTTERFLY VALVE_CONCENTRIC & OFFSET DIFFERENCE

    Wafer Type Butterfly Valve:

    The wafer type butterfly valve (Figure 4) is the most economical version and it is sandwiched between two pipe flanges and the flange bolts surround the valve body. The pipe flanges are connected through long bolts that cross the entire valve body. The sealing between the valve and pipe flanges is accomplished by using a tightly fitted seal, such as an O-ring, gasket, precision machined, along with a flat valve face on the downstream and upstream sections of the valve. This type of connection is designed for sealing against bi-directional differential pressures and to prevent backward flow in systems designed for universal flow.

    Figure 4

    WAFER TYPE BUTTERFLY VALVE

    Lug Type Butterfly Valve:

    The lug-style butterfly valve (Figure 5) has threaded lugs outside the valve body. Two sets of bolts connect pipe flanges to each side of the bolt inserts without nuts. This design enables the disconnection of one side without affecting the other for dead-end service. Lug-style butterfly valves used in dead end service generally have a lower pressure rating.

    Figure 5

    LUG TYPE BUTTERFLY VALVE

    Double Flange Butterfly Valve:

    The Double Flange Butterfly Valve have flanged end on both sides of valve. The valve is connected to piping flanges through bolts. The double flange butterfly valve body configuration ensures precise installation in piping and can also be used as an end to the piping line, if required. The unique feature of this valve is its adaptability for lined pipes due to negligible disc protrusion beyond the body laying length. This also ensures installation close to other pipe fittings.

    This article is written by

    Mr. Goutham Rathinam

    (BE-Mechanical & CSWIP 3.1-TWI,UK)             

    Email ID: goutham.r86@gmail.com

  • Ball Valves – What is a Valve (Part – 5)

    Ball Valves – What is a Valve (Part – 5)

    In the Valves Part-1, we discussed what is a valve, its history, and its categorization (Click here to read).

    In Part-2, we discussed about Globe valves (Click here to read).

    In Part-3, we discussed about Gate valves (Click here to read).

    In Part-4, we discussed about Plug valves (Click here to read).

    In this part, we will learn about Ball Valves.

    Ball Valve:

    The ball valve is a quarter-turn operated valve. The closure member is a spherical plug with a through-hole. When the valve is in the open state, the through-hole is in-line with the fluid flow and hence, the fluid passes through it. The valve is closed by rotating the globe by 90 Deg. such that the hole now becomes perpendicular to the flow and hence, stops the flow.

    The seat is usually circumferential, made up of soft materials to offer a tight shutoff. The seat can be made either out of plastic or metals. Ball valves are not recommended to be used in a partially open condition. Due to misalignment between the flow direction and opening of the plug, a large pressure drop takes place in the partially open condition.

    There are four general body styles of ball valves, Namely;

    • Split-body ball valve
    • Top-entry ball valve
    • End-entry (Side-entry) ball valve
    • Three-piece body ball valve

    The difference is based on how the pieces of the valve are manufactured and assembled, but the valve operation is the same in each type. Each design has its benefits.

    Split-body ball valve (Figure 1) design consists of a two-part body, a cover, ball, seat rings, stem, and other internals. The two-part body is held together by a flange connection. One body part is smaller than the other. The ball is inserted in the larger body part, and the smaller body part is assembled by a bolted connection. The stuffing box is constructed integrally with the larger body part. On smaller size split-body ball valves, the two-part body is joined by a threaded connection. The flanged or threaded joint between the two-part body is an added source of potential leakage.

    Figure 1

    Split-body ball valve

    Top-entry ball valves (Figure 2) allow access to valve internals for assembly, dis-assembly, repair, or maintenance by removal of the valve bonnet-cover. The valve is not required to be removed from the pipeline.

    Figure 2

    Top-entry ball valves

    End-entry (Side-Entry) ball valves (Figure 3) have a single-piece body. The ball is inserted from one end and is retained by an insert. These valves have flange- or screwed-end connections. This design is commonly used for inexpensive small valves.

    Figure 3

    End-entry (Side-entry) ball valves

    Three-piece body ball valve’s (Figure 4) middle part is the major part that holds all valve internals, and the stem passes through a hole in the top. Two end caps are held together with the middle body by bolts or studs and nuts. The end connections are part of the end caps, and they may be butt-welding, socket welding, threaded, or flanged.

    Figure 4

    Three-piece body ball valve

     

     

    There are three types of ball valves based on ball movement, Namely;

    • Trunnion mounted ball valves
    • Floating type ball valves
    • Rising stem ball valves

    Trunnion mounted ball valve (Figure 5) has additional mechanical anchoring at the top and bottom on the ball. This special mounting is suitable for larger and higher-pressure valves. Moreover, this design allows for a reduction in valve torque as the ball is supported in two places. The trunnion mounted stem absorbs the thrust from the line pressure, preventing excess friction between the ball and seats, so even at full rated working pressure operating torque remains low.

    Figure 5

    Trunnion mounted ball valve

    Floating Ball Valve is not held in place by a trunnion, and instead is attached only to the stem. This sometimes causes the ball to float slightly downstream. However, when this happens, the ball presses against the seat, creating a positive seal.

    Rising Stem Ball Valve incorporates tilt-and-turn operation, eliminating seal rubbing which is one of the primary causes of valve failure. When the valve is closed, the core is wedged against the seat, ensuring positive shutoff. When the valve is open, the core tilts away from the seal and the flow passes uniformly around the core face. The Rising stem ball valve utilizes this operating principle, delivering fast, low-torque operation and long-term reliable performance. Additionally, the valve can eliminate localized high- velocity flow that typically creates uneven seat wear exhibited by an ordinary ball, gate, and plug valves.

    Additionally, there are three basic types of bores for ball valves: Namely Full port, Reduced port (also known as Standard port), and V-port. These four types have different constructions and purposes.

    Full-Port Ball Valve (Figure 6) also known as a full-bore ball valve has a bore internal diameter (ID) approximately equal to the pipeline ID. This allows for reduced friction and pressure loss across the valve. With a full-port ball valve, there is no restriction to the flow of fluid, but the valve can be more expensive. This type of bore is ideal for situations where pigging may be necessary. The Cameron TBV series split-body, full-port, flanged ball valve combines its sealing technology and design expertise with the versatility to solve even the most demanding applications. This technology is widely used in the chemical, petrochemical, and refining industries.

    Reduced-Port Ball Valve (Figure 6) also known as a reduced-bore ball valve is a valve in which the bore is reduced to one or two nominal sizes lower. This provides a more restricted flow path, generally resulting in higher energy losses. Known for its robust design, superior sealing areas, and stainless-steel overlays, it is widely used for the oil and gas industry’s most severe service applications.

    Figure 6

    FULL & REDUCED PORT BALL VALVE

    V-Port Ball Valve has either a “v” shaped ball or a “v” shaped seat. This type of valve also is known as a control valve in which the flow velocities need to be controlled as required per the application.

    This article is written by

    Mr. Goutham Rathinam

    (BE-Mechanical & CSWIP 3.1-TWI,UK)             

    Email ID: goutham.r86@gmail.com

  • Low Hydrogen Electrodes

    Low Hydrogen Electrodes

    Low Hydrogen electrodes are very popular in the industries because of the following reasons;

    1. Ability to produce X-ray quality welds
    2. Good weld bead appearance
    3. Ability to weld thicker material with high deposition rates
    4. Less susceptible to failures and cracks especially Hydrogen Induced Cracks
    5. Sound weld metal properties with good toughness
    6. A smooth, stable and quiet arc with less spatters
    7. Good penetration and deposition rate
    8. Easy initiation of arc and good control over the arc for welders
    9. Faster post-weld cleaning
    10. Ability to join steels with poor weldability such as high carbon steels, low alloy steels, etc.

    The above benefits have made low hydrogen electrodes the first choice for welding critical components that are prone to failures during service or which involves several hazards and dangers.

    Why low Hydrogen electrodes are so beneficial?

    The reason behind the above-mentioned qualities lies in the covering or the flux materials. The covering (flux) of a low Hydrogen electrode has two unique features;

    1. Low Hydrogen content: The Hydrogen content or the amount of Hydrogen in the covering of such electrodes is very low. A higher level of hydrogen in weld metal possesses risks of brittle failures and delayed cracking or Hydrogen Induced cracking. Hence, a lower level of hydrogen covering in the electrode will ensure that only a limited amount of hydrogen will enter into the weld metal, which can prevent the above-mentioned failures.

    2. Contains basic minerals: The basic minerals in electrode coverings imply that the chemicals present in the covering reduce the oxygen content in the weld and minimize the harmful oxide inclusions at the grain boundaries of the microstructure, which results in a cleaner weld with high toughness.

    Which electrodes are known as Low Hydrogen electrodes?

    The following electrodes are known as low hydrogen electrodes;

    • Exx15 (E7015)
    • Exx16 (E7016)
    • Exx18 (E6018, E7018)
    • Exx28 (E7028)
    • Exx48 (E7048)

    The following table (Table – 1) gives a list of all low hydrogen electrodes, type of covering, applicable welding positions and type of current and polarity required;

    Table – 1

    Electrode classification (AWS 5.1) Type of covering Applicable welding positions

    Current and polarity

    E6018

    		 Low-hydrogen potassium, iron powder F, V, OH, H AC or DCEP

    E7015

    		 Low-hydrogen sodium F, V, OH, H DCEP
    E7016 Low-hydrogen potassium F, V, OH, H

    AC or DCEP

    E7018

    		 Low-hydrogen potassium, iron powder F, V, OH, H

    AC or DCEP

    E7028

    		 Low-hydrogen potassium, iron powder H-fillet, F

    AC or DCEP
    E7048 Low-hydrogen potassium, iron powder F, OH, H, V-down

    AC or DCEP
    Where,

    • F – Flat, V – Vertical, OH – Overhead, H – Horizontal, H-fillet – Horizontal Fillet
    • AC – Alternating Current
    • DCEP – Direct Current Electrode Positive (Reverse Polarity)

     

    What happens if Hydrogen will be present in the weld metal?

    From the above discussion, it is clear that a low hydrogen electrode is used to prevent failures or cracks by restricting Hydrogen from entering into the weld metal. Nevertheless, what will happen if a significant amount of Hydrogen will enter into the weld metal? or how the lower level of Hydrogen ensures good welding?

    If a significant amount of Hydrogen atoms gets dissolved into the weld metal and doesn’t get any chance to escape then delayed cracking occurs. Delayed cracks may occur after several hours or days of solidification of weld metal.

    Such cracks may occur parallel to the fusion boundary and within the heat-affected zone or may originate in the weld deposit also. It is also known as underbead cracking.

    If molten weld puddle is rapidly cooled, then two things may happen;

    1. The resulting crystal structure will be a mixture of ferrite and carbide: Hydrogen is almost insoluble in ferrite, Hence the Hydrogen atoms will escape or diffuse from the weld metal and the weld metal will be more ductile and crack resistant.

    2. The crystal structure will be transformed into martensite: The Hydrogen atoms do not diffuse from a martensitic crystal structure and gets trapped in the weld metal. Hence, chances of getting crack will be more. To prevent this preheating may be carried out. Preheating of base metals essentially slows down the cooling rate and helps in diffusion (escape) of Hydrogen atoms from weld metal

    Baking of Low Hydrogen Electrodes:

    Low-hydrogen electrodes must be kept free from moisture and other contaminants. Because moisture/water is a potent source of hydrogen.

    To prevent the electrodes from moisture contamination, they are frequently packed and supplied in hermetically sealed containers.

    The electrodes must be baked before using, as per the recommendation of the manufacturer. However, preliminary guidance for baking is available in ASME Section II Part C; an extract is available in table 2 of this article;

    Table -2 

    Electrodes (As per AWS 5.1)

    		 Holding Ovens

    Drying Conditions 

    E6018

    E7015

    E7016

    E7018

    E7028

    E7048

    		 50°F to 250°F

    [30°C to 140°C]

     

    500°F to 800°F

    [260°C to 425°C]

    1 to 2 hours at temperature

     

    The E7018 electrode is one of the most preferred low hydrogen electrodes in the industries. It contains a sufficient amount of iron powder in the covering and works best if used with direct current reverse polarity (DCEP).

    Due to the presence of iron powder, a higher deposition rate is achieved and it quiets the metal transfer. The weld quality and bead appearance are very good.

    The coverings of E7018 and E7015 electrodes are similar, except for the addition of a slightly higher percentage of iron powder in E7018 covering. The coverings on these electrodes are relatively thicker than those of the E7016 electrodes.

    The E7016 is designed for direct current AC; The E7015 is similar to the E7016 but operates with DC.

    The covering of the E7028 electrode is quite thick and contains a high iron powder content. Their deposition rate is the highest among all the low-hydrogen electrode types. However, they can be used in a horizontal and flat position.

    The E7048 class is similar to the E7018 type but designed for downhill applications only

    Mandatory and Optional Supplemental Designators on electrodes:

    An electrode is identified by the following;

    • mandatory classification designators
    • optional supplemental designators

    For Example EXXXX-1 HZR

    The first four-letter after ‘E’ are known as mandatory classification designators and the digits and numbers given after hyphen (-) are known as optional supplemental designators and these are optional hence may be used depending upon the requirements.

    Now, we will understand the meaning of mandatory classification designators;

    In E7018:

    • The letter ‘E’ stands for an electrode
    • The first two digits i.e. ‘70’ denotes the minimum tensile strength i.e. 70 Ksi (or 70000 Psi)
    • The second last digit i.e. ‘1’ indicates the position in which the electrode can be used. In particular, the letter ‘1’ depicts all positions
    • The last two digits together show the polarity and the flux composition of the electrode.

    To read more about the electrode symbols and their meaning please click here

    As we have understood about the mandatory electrode designators, now we will understand about the optional supplemental designators;

    In EXXXX-1 HZ R 

    ‘1’ indicates that the electrodes (E7016, E7018, or E7024) meet the requirements for improved;

    • Toughness for electrode E7016 and E7018
    • Ductility for electrode E7024

    ‘HZ’ Designates that the electrode meets the requirements of the diffusible hydrogen test with an average value not exceeding “Z” mL of Hydrogen per 100 g of deposited metal, where “Z” is 4, 8, or 16.

    For Example, E7018-H4R indicates 4ml (avg) diffusible hydrogen content in 100g of deposited weld metal

    Finally the last optional designator i.e. ‘R’ Designates that the electrode meets the requirements of the absorbed moisture test. The electrode is exposed to an environment of 80°F [27°C]/80% relative humidity (RH) for not less than nine hours by any suitable method for the moisture test.

  • What is stainless steel

    What is stainless steel

    This article covers the following topics/questions;

    • What is stainless steel?
    • Types of stainless steel.
    • Is stainless steel magnetic?
    • Stainless steel welding and weldability.
    • How to select the welding rod or filler wire?

    we will start this article with the first topic/question i.e what is stainless steel?

    WHAT IS STAINLESS STEEL?

    Stainless steels (SS) are essentially iron base alloy steels containing at least 10.5 % Chromium. Other important alloying elements that may be present in stainless steel are carbon, Nickel, Manganese, etc.

    “SS’ is an abbreviation used for stainless steel in the industries.

    Due to the presence of chromium, a very thin chromium-rich oxide layer is formed on the outer surface of stainless steel. This chromium-rich oxide layer has two unique features;

    1. Passive layer: Due to passive (inactive) in nature, this layer does not reacts with the environment (especially oxygen – the major cause of rusting) and prevents oxidation hence the stainless steel remains safe and free from rust.

    2. Self-repairable: Whenever the chromium-rich oxide layer is damaged, a new layer is formed quickly. Hence, the stainless steel will remain rust-free. However, the rate at which the chromium oxide passive film is developed depends on its chromium content.

    Polished stainless steel remains bright under most environmental conditions.

     

    TYPES OF STAINLESS STEELS

    There are five main types (or grades) of stainless steel, these are the following;

    1. Austenitic stainless steel – FCC (face-centered cubic) crystal structure
    2. Ferritic stainless steel – BCC (body-centered cubic) crystal structure
    3. Martensitic stainless steel – BCT (body-centered tetragonal) crystal structure
    4. Duplex stainless steel – FCC + BCC i.e. mixture of Austenite and Ferrite
    5. Precipitation-hardening (PH) stainless steel

    Out of these five types, the first four i.e. Austenitic, Ferritic, Martensitic, and duplex are categorized according to their crystal structure and if they are additionally strengthened by the precipitation hardening process then the product obtained is known as Precipitation-Hardening (PH) stainless steel.

    In addition to the above-mentioned types, some advanced types (or specialty grades) of stainless steels are also being used in the industries, these are;

    • Superaustenitic Stainless steel
    • Superferritic stainless steel
    • Supermartensitic stainless steel
    • Superduplex stainless steel

    The austenitic stainless steel can be further divided into two types;

    1. Austenitic stainless steel containing Chromium and Nickel as the main alloying elements (In addition to Iron) – These are identified as AISI 300 Series types.
    2. Austenitic stainless steel containing Chromium, Nickel, and Manganese as the main alloying elements (In addition to Iron) – These are identified as AISI 200 Series types.

    Ferritic stainless steels contain chromium as the major alloying element and are identified as AISI 400 series types.

    Martensitic stainless steels also contain chromium as the main alloying element (In addition to Iron and Carbon) and identified are AISI 400 series types.

     

    *************************

    A very important question, which comes to our mind, is;

    Is stainless steel magnetic?

    In general, the Austenite stainless steels are non-magnetic, a term paramagnetic is also used for non-magnetic elements. Hence, we can say that Austenitic stainless steels are paramagnetic. This concept will be discussed later on in this article.

    *************************

    Table 1, gives a general summary of types of Stainless steel and their corresponding identification No. (As per the AISI Classification system), detrimental alloying elements, Main types/grades, and P Numbers (As per ASME Sec IX).

    Table – 1

    Type of Stainless Steel

    		 AISI Classification system Major Alloying Elements Main types/grades (AISI) P number

    (ASME Sec IX)

    Austenitic stainless steel

    		  

    2XX

    		 Chromium + Nickel + Manganese

    201

    202
    3XX Chromium + Nickel 301

    302, 302 B

    303. 303Se

    304, 304H, 304L, 304LN, 304N

    305

    308

    309, 309S

    310, 310S

    316, 316H, 316L

    317, 317L

    321

    330

    334

    347

    348

    384

     

    8

    Ferritic stainless steel

    		 4XX Chromium  

    405

    409 – 10/20/30

    429

    430, 430Ti

    434

    436

    439

    442

    444

    446

     

    7
    Martensitic stainless steel 403

    410

    414

    416

    420

    422

    431

    440A, 440B, 440C

    6

     

    Now, we shall discuss the three important types of stainless steel i.e Austenitic, Ferritic, and Martensitic stainless steel, properties & grades, weldability, and suitable filler metal/electrodes.

    1. AUSTENITIC STAINLESS STEEL:

    Austenitic stainless steels are the most widely used stainless steel in the world. They have a face-centered cubic (FCC) crystal structure and are nonmagnetic (also known as paramagnetic) in the annealed condition. However, the magnetic properties of austenitic stainless steel can be increased by cold working.

    The chromium content is generally above 16% in austenitic stainless steels and total chromium, nickel, manganese, and silicon content over 25% by weight, They are popular among industries for;

    • Good ductility
    • Excellent strength
    • Good corrosion resistance
    • High toughness
    • Excellent cryogenic properties
    • Excellent strength and oxidation resistance at high temperatures.

    Austenitic stainless steel based mainly on the Iron-Chromium-Manganese-Nitrogen is identified by a three-digit number system starting with 2, such as 201 and 202. Whereas, alloys based on the Iron –Chromium-Nickel-Carbon are also identified by a three-digit number system but starting with 3 for example, 304 and 309, etc.

    Due to face-centered-cubic (FCC) crystal structure, austenitic stainless steels have better toughness and ductility than carbon steels and alloy steels. The notch toughness at cryogenic temperatures is also excellent.

    Type 316H stainless steels possess the best stress-rupture behavior of the Series 300 austenitic stainless steel.

    Weldability of austenitic stainless steel:

    Austenitic stainless steels possess higher thermal expansion than ferritic or martensitic stainless steels.

    Distortion or warping occurs during the welding of austenitic stainless steel due to it’s high coefficient of thermal expansion and low thermal conductivity.

    Austenitic stainless steel is susceptible to solidification and liquation cracking. Hence, proper care to be given while selecting filler material and welding process.

    Submerged arc welding (SAW) is not preferred when a fully austenitic stainless steel or low ferrite content weld deposit is required.

    Table – 3, gives a guide for the selection of proper filler wire or welding rods as per the base material (for austenitic stainless steel).

    Table – 3

    Type of austenitic stainless steel

    		 Filler Metal/Welding rods
    SMAW

    (Covered Electrodes)

    		 GMAW, GTAW, PAW, SAW

    (Bare welding rods)

    FCAW

    (Tubular flux-cored welding rods)

    201, 202

    		 E308, ER209, E219 ER308, ER209, ER219 E308TX-X

    301, 302, 304, 305

    		 E308 ER308

    E308TX-X

    304L

    		 E308L, E347 ER308L, ER347

    E308LTX-X, E347TX-X

    309

    		 E309 ER309

    E309TX-X
    309S E309L, E309Cb ER309L

    E309LTX-X, E309CbLTX-X

    310, 314

    		 E310 ER310

    E310TX-X

    310S

    		 E310, E310Cb ER310

    E310TX-X

    316

    		 E316 ER316

    E316TX-X

    316L

    		 E316L ER316L

    E316LTX-X

    316H

    		 E16-8-2, E316H ER16-8-2, ER316H

    E316TX-X

    317

    		 E317 ER317

    E317LTX-X

    317L

    		 E317L ER317L

    E317LTX-X

    321

    		 E308L, E347 ER321

    E308LTX-X, E347TX-X

    330

    		 E330

    ER330

    –

    347, 348

    		 E308L, E347 ER347

    E308LTX-X, E347TX-X

    Where,

    • N – Addition of Nitrogen
    • H – High Carbon content
    • L – Low Carbon content

     

    2. FERRITIC STAINLESS STEEL:

    Ferritic stainless steels are essentially iron-chromium-carbon alloys with a nominal of 11% to 30% chromium along with other ferrite stabilizers, such as molybdenum, aluminum, niobium, or titanium.

    They possess a body-centered cubic (BCC) crystal structure. These steels exhibit good ductility and have good resistance to stress corrosion cracking, pitting, and crevice corrosion.

    Ferritic stainless steels with Low chromium (Approx 11%) such as Type 409, are commonly used in automotive exhaust systems. Ferritic stainless steel alloys having an intermediary level of chromium content (16% to 18%) are often used in food handling and automotive trim applications. High chromium content ferritic stainless steel with additions of molybdenum (often referred to as superferritic stainless steels) are commonly used in applications that require high levels of oxidation and corrosion resistance such as heat exchangers and piping systems for seawater.

    Types 430, 442, and 446 are referred to as the first-generation ferritic stainless steels. They contain mainly chromium as a ferrite stabilizer along with relatively high carbon content.

    They often require PWHT otherwise intergranular corrosion may occur. They also exhibit low toughness.

    Whereas, Types 405 and 409 are referred to as the second-generation ferritic stainless steels. They have lower chromium and carbon content but contain ferrite formers.

    These steels are also referred to as pseudoferritic because they require other ferrite formers in addition to chromium.

    They are comparatively less costly, possess good fabrication characteristics, and have useful corrosion resistance than the first-generation ferritic stainless steels but they often possess low toughness.

    Weldability of ferritic stainless steel:

    Generally, fewer precautions are required during welding because they cannot be hardened by quenching. Hence, the chances of martensite formation are less during the cooling of weld metal. However, Types 430, 434, 442, and 446 are exceptional cases due to the presence of both high chromium and high carbon content. The risk of hydrogen-induced cracking during cooling is more in these alloys especially when welding is carried out under high restraint conditions such as heavy weldments or surfacing welds on carbon steel. To minimize residual stresses that contribute to weld, preheating of 150°C (300°F) or higher can be used.

    Chances of Hydrogen embrittlement increases in ferrites stainless steel when martensite is present along ferrite grain boundaries in the weld metal or HAZ. However, Ferritic stainless steels are less susceptible to hydrogen embrittlement if compared to martensitic stainless steel.

    The risk of solidification cracking in ferritic stainless steels is comparatively very less because the primary solidification phase is ferrite. However, Alloys with additional alloying elements like titanium and niobium or high impurity levels are more susceptible to solidification cracking

    Ferritic Stainless Filler Metals:

    To weld ferritic stainless steels with ferritic stainless steels or to any dissimilar steel, Filler metal/welding electrode of the following types can be selected;

    1. Filler metals with compositions approximately matching to those of the base metals
    2. Austenitic stainless filler metals (Types 309 and 312)
    3. Nickel-alloy filler metals (ERNiCr-3, ENiCrFe-2, or ENiCrFe-3)

    Filler metals/welding rods matching Types 409 and 430 stainless steels (base metal) are widely available. However, whenever ferritic stainless steels are used as filler metal, the resulting welds lack in toughness properties in both the weld metal and the HAZ

    Filler metals made up of Austenitic stainless steel such as Types 309 and 312 or nickel-alloy filler metals such as ERNiCr-3, ENiCrFe-2, or ENiCrFe-3 often are selected for joining ferritic stainless steels to ferritic stainless steels or any dissimilar metals.

    Type 444 stainless steel can be welded to matching steel with Type 316L weld metal and Type 430 steel can be welded with E308 and E308L.

    when welding ferritic stainless steels to ferritic stainless steels or mild or low alloy steels, nickel alloys, and copper-nickel alloys, Nickel-alloy filler metal, such as ERNiCr-3, ENiCrFe-2, or ENiCrFe-3, can be used which produce sound weld joints.

    However, Austenitic stainless steels are generally less resistant to stress corrosion cracking (SCC) than ferritic stainless steel alloys. Hence, proper consideration must be given before choosing filler metals.

    To weld Low-chromium ferritic stainless steels, such as 405 and 409 with mild steel, carbon steel filler metals can be used with proper care to avoid excessive dilution.

    Preheat and PWHT requirements:

    The preheating requirements are determined largely by job thickness, chemical composition, desired mechanical properties, and restraint conditions.

    Ferritic stainless steels with low chromium or high-carbon content can be preheated within the range of 150°C to 230°C (300°F to 450°F).

    PWHT for first-generation ferritic stainless steels (Types 430, 442, and 446) can be conducted at temperatures ranging from 700°C to 840°C (1300°F to 1550°F). These temperature ranges help prevent further grain coarsening.

    Whereas, PWHT for Second-generation ferritic stainless steels (Types 405 and 409) can be conducted at higher temperatures up to at least 1040°C (1900°F)

     

    3. MARTENSITIC STAINLESS STEEL

    Martensitic stainless steels were the first stainless steel to be produced in the world. As mentioned above they are essentially iron-chromium-carbon alloys with a nominal of 11.5% to 18% chromium.

    They are hardenable by appropriate heat treatments and can also be hardened by cold working.

    Martensitic stainless steel can be transformed into austenite when heated beyond 1010°C (1850°F). However, rapid cooling from this temperature will again result in a martensitic microstructure.

    These steels are popular for

    • Relatively low cost.
    • Moderate corrosion resistance,
    • Oxidation resistance,
    • Lacks toughness and require tempering for adequate toughness
    • Ability to develop a wide range of mechanical properties

    Martensitic stainless steels are used to fabricate a variety of products, for example, Low and medium carbon martensitic stainless steels are typically used in jet engines, steam turbines, and gas turbines. High carbon martensitic stainless steels are used for gears, shafts, cams, ball bearings, and valves, etc.

    Weldability of Martensitic stainless steel:

    Martensitic stainless steels often produce hardened HAZs, and as the hardness of HAZ increases, it’s toughness decreases, and susceptibility to Hydrogen induced cracking increases.

    As a general practice, post weld heat treatment (PWHT) is given to martensitic stainless steel welded joints, to improve the weld properties.

    It’s weldability, in general, increases when an austenitic type filler metal or welding rod is used.

    Since Martensitic stainless steels are subject to hydrogen-induced cracking hence proper precautions must be taken in the selection of welding process, handling, and storage of the filler metal and cleanliness to avoid hydrogen from entering into the weld metal.

    Following Welding processes can be employed to weld Martensitic stainless steel

    1. Arc Welding
    • Shielded Metal Arc Welding (SMAW) or stick welding
    • Gas Metal Arc welding (GMAW) or MIG Welding
    • Gas Tungsten Arc Welding (GTAW) or TIG welding
    • Flux Cored Arc Welding (FCAW)
    • Plasma Arc Welding (PAW)
    • Submerged Arc welding (SAW)
    2. Resistance Welding
    • Resistance Spot Welding
    • Resistance Flash Welding
    3. Electron beam welding
    4. Laser beam welding
    5. Friction welding
    6. High frequency welding
    Filler metal/Welding Rod for martensitic type stainless steels:

    The three most commonly used filler metal grades for martensite stainless steel are;

    • E410/ER410
    • E410 NiMo /ER410 NiMo
    • E420/ER420

    Filler metal type 410 (E410/ER410) can be used to weld the following martensitic stainless Types;

    • 403
    • 410
    • 414
    • 420

    Type 410 NiMo filler metal is used to weld Type CA-6NM castings (cast martensite stainless steel)

    Filler metal ER420 is used to weld type 420 stainless steel when the main goal is matching the carbon content of base metal with filler metal. This filler metal may also be used for surfacing of carbon steels to provide good corrosion and wear resistance.

    However, martensitic stainless steel welding lacks good toughness properties (except for ER410NiMo), hence PWHT is carried to achieve good toughness (If required).

    To achieve good weld metal toughness property, austenitic stainless steel filler metal type 308 (E308/ER308) & 309 (E309/ER309) can also be used to weld martensitic stainless steels to martensitic stainless steels or any other types of stainless steels.

    For Types 416 and 416Se steels that are free-machining grades, E312-15 austenitic stainless steel filler metal may be used for welding.

    Preheat and PWHT requirements:

    Preheat and post weld heat treatment (PWHT) requirements for martensitic stainless steel are given in Table – 2.

    Table – 2

    Carbon content (%)

    		 Preheat temperature (minimum) Requirements for PWHT

    °C

    °F

    <0.05

    		 121 250 Optional

    0.05–0.15

    204

    		 400 Recommended
    >0.15 316 600

    Mandatory

     

     

  • Underwater Welding

    Underwater Welding

    Underwater welding is used for repairing ships, offshore structures including oil drilling rigs, and pipelines that are submerged in water.

    Taking out the damaged components from the sea for repair purposes is a costly and time-consuming task. Hence, to save time and money, underwater welding is preferred for the repair works (wherever possible)

    Russian metallurgist Konstantin Khrenov invented it in 1932. However, British Admiralty – Dockyard performed the first-ever underwater welding for sealing their leaking ship rivets.

    ‘Van der Willingen’ of Holland developed first waterproof electrodes in 1946

    Underwater welding is carried out at elevated pressure. Due to high pressure, the welding processes behave differently like changing of arc behavior, increase in arc voltage with an increase in pressure, etc.

    Types of underwater welding:

    Underwater welding can be categorized into two types, these are the following;

    1. Wet underwater welding
    2. Dry underwater welding (also known as hyperbaric welding)

    Wet underwater welding:

    As the name suggests, it is carried out directly in the water itself. Hence, the welder is completely exposed to the water and the surrounding elements.

    Shielded Metal Arc Welding (SMAW/MMAW) or stick welding with a waterproof electrode is the most commonly used welding process in these conditions.

    A constant current welding machine is used for this operation. Direct current (DC) at 300–400 Amps used to power the electrode during these conditions.

    The electrode holders of SMAW or stick welding are heavily insulated and designed for water cooling.

    A heavy-duty isolation switch is installed in the welding cable to disconnect the welding current when not in use. The welder gives the necessary instructions to the surface operator connect/disconnect. The current always remains disconnected when not in use.

    https://youtu.be/aE4Dtl2IBJo

    Other welding processes that could be employed during these conditions are;

    • Flux-Cored Arc Welding (FCAW)
    • Friction welding.

    The temperature is very low, especially at greater depths. Hence, the risk of welding failure due to rapid cooling of the molten weld pool may not be avoided. Low carbon equivalent steels can give good results, especially at greater depths, because of hydrogen-caused cracking.

    Dry underwater welding:

    It is also known as hyperbaric welding. An especially constructed enclosure or chamber (also known as habitat) is used to surround the component to be welded and the welder.

    The chamber must be sufficient to accommodate the welder as well as the component to be welded. A mixture of gases (typically a mixture of helium and oxygen, or argon) is used to prevent water from entering through the openings.

    Following welding processes may be used for dry hyperbaric welding;

    • Shielded metal arc welding (SMAW) or stick welding,
    • Flux-cored arc welding (FCAW),
    • Gas tungsten arc welding (GTAW) or TIG welding
    • Gas metal arc welding (GMAW) or MiG Welding
    • Plasma arc welding (PAW)

    However, Gas tungsten arc welding (GTAW) or TIG welding is most commonly used during these conditions.

    Quality of underwater welding:

    Dry hyperbaric welding often gives good weld quality as compared to wet welding, due to a better or increased control over the physical conditions. Hence, dry welding is preferred over wet welding especially when the quality of the weld is of utmost importance.

    Moreover, heat treatments (Preheat or post heat) operations are also possible during dry hyperbaric welding.

    Non-destructive tests are also employed out to check the quality of welds as per requirements.

    Classes of welds:

    The weld metal properties vary with pressure and cooling rates. Hence the underwater weld metal properties usually differ from the welds made above water.

    The American Welding Society (AWS) publishes a code AWS D3.6 for Underwater Welding. This document defines three weld classes, these are;

    1. Class A weld

    2. Class B weld

    3. Class C weld

    4. Class O weld (discontinued from 2010)

    The following organizations develop underwater welding standards;

    • American Society of Mechanical Engineers (ASME)
    • American Welding Society (AWS)
    • Det Norske Veritas
    • Bureau Veritas
    • International Institute of Welding

    Underwater welding salary:

    Underwater welding career is very lucrative and the opportunities are unlimited. They work in the construction, surveying, and repair in both fresh- and saltwater.

    The salary of an underwater welder is determined by the following:

    • Their Employer
    • Their Location
    • Depth of the dive
    • Previous Experience

    However, the annual salary for underwater welders may start at $20,000 per year but it may go as high as $300,000 per year.

    Underwater welding dangers:

    • Electric Shock: During wet underwater welding, Chances of electric shock may not be avoided due to the presence of water. In SMAW. An electric arc is generated which produces the necessary heat for welding. During the generation of arc, shielding gases are produced which prevents the molten weld pool from coming in direct contact with the water. The electrode holders are heavily insulated and heavy-duty isolation switches are used to prevent any unwanted shocks.
    • High differential pressure: As depth increases, the water pressure increases. However, the biggest danger is the differential pressure also known as “Delta P” (ΔP) hazards. Which occurs when two water bodies intersect each other with a different water level, such as a dam. Due to the difference in depth, Water tends to fall from one body to the next with great force and hence pressure difference is created. Which is undetectable and tough for the diver to escape.
    • Diving risks: During diving, the welder may be subjected to hypothermia, drowning and decompression sickness also known as “the bends”.
    • Explosion: The pressurized gases in a dry chamber or habitat may create erratic arc behavior, which increases the risk of electric shock or explosion.

    There are about 10-15 deaths per year due to drowning and electrocution.

    Underwater welding certifications:

    Primarily the underwater welders must be having a commercial diving certificate and should be a certified welder.  The required certifications may be the following;

    • Welding certificate
    • Diving Certificate
    • Riggers Certificate
    • Safety Certificates
    • NDT certificates

    The AWS D3.6 (Underwater Welding Code) is an internationally recognized code for the welding of structures underwater in both wet and dry environments.

    How to become an underwater welder:

    To become an underwater welder, these are the following minimum requirements;

    • High school diploma or GED
    • Ability to swim
    • Commercial Diving Certification
    • AWS Certified Welding Training

    First, you must attend a commercial diving course. After becoming a successful commercial diver, you can work as a diver tender or apprentice diver with a diving company, which provides welding services also. During that, you can get underwater welding training necessary to pass the qualification tests per ANSI/AWS D3.6. After passing the qualification exam, you can become an underwater welder.

    Underwater welding videos:

    Here are some of my favorite videos on underwater welding, which you may like;

     

     

     

  • Plug Valves – What is a Valve (Part – 4)

    Plug Valves – What is a Valve (Part – 4)

    In the Valves Part-1, you learned what is a valve, its history, and its categorization (Click here to read).

    In Part-2, you learned about Globe valves (Click here to read).

    In Part-3, you learned about Gate valves (Click here to read).

    In this, you are going to learn about Plug Valves categorized by design.

     

    Plug Valve:

    Plug valve is a quarter-turn manual valve that uses a cylindrical or tapered plug to permit or prevent straight-through flow through the body. With a full-port design, this opening is the same as the area of the inlet and outlet ports of the valve.

    Plug valves can be applied to both On-Off and Throttling services. Plug valves were initially designed to replace gate valves since plug valves by virtue of their quarter-turn action can open and close more easily against flow than a comparable gate valve.

    The typical plug valve consists of a body, bonnet, stem, and plug. The seat is an integral part of the body in case of a lubricated plug valve. For a non-lubricated plug valve, a non-metallic seat is used to improve leak tightness of the valve.

    There are four types of Plug Valves. Namely: Lubricated, Non-lubricated, Eccentric Plug & Expanding Plug.

     

    Lubricated plug valve (Figure-1) uses a lubricant usually made up of a base oil and viscosity improver (like amorphous or fumed silica) that is injected under pressure between the plug face and body seat to reduce friction and seal ports. Valve manufacturers generally recommend lubricants suitable for the process fluid, and the valves often must be resealed after only a few cycles, and in some cases, after every cycle. Considered a high maintenance plug valve, they are often used in applications that have infrequent operations. Lubricated plug valves perform well in processes that utilize fluids that carry mildly abrasive particles such as dirty upstream applications, gas pipeline systems that need bypass valves, and blow-down valves on valve stations.

    Figure-1

    Lubricanted Plug valve
    Lubricated Plug valve

     

    Non-Lubricated Plug Valve (Figure-2) utilizes a tapered or cone-shape that acts as a wedge and presses a polymeric sleeve against the body cavity. The use of the sleeve reduces friction between the plug mechanism and the body.  Non-lubricated plug valves are often used instead of lubricated ones in applications where maintenance needs to be kept to a minimum, such special services in sulfur, hydrogen fluoride, or where liquids could be trapped or solidify and potentially jam the valve. However, non-lubricated plug valves are limited by temperature and chemical compatibility of the non-metallic materials they are made of.

    The three main types of non-lubricated plug valves are:

    Lift-type plug valve

    Elastomer sleeved plug valve

    Fully lined plug valve

    Figure-2

    Non-Lubricated Plug Valves

     

    Eccentric Plug Valve (Figure-3) uses a half plug that is advantageous for applications needing a higher seating force with minimal friction from open to closed position. The torque seated valves also feature improved shut off capabilities. Eccentric plug valves are used for a wide range of flow control and isolation applications including clean and dirty water, sewage, sludge and slurries, air, and other services.

    Figure-3

    Eccentric Plug Valve

     

    Expanding Plug Valve (Figure-4) uses multiple components that allow the valve to mechanically expand and give it a true double block and bleed function in one valve. The plug valve uses a mechanism that rotates between the open and closed positions and protects both seals from the flow path. During rotation, there is no contact between body and seals, and slips expand onto the body seat when the valve is closed to avoid causing any wear or abrasion to the seals. They are often used to prevent product contamination in applications that do not require double isolation.

    Figure-4

    Expanding Plug Valve

     

    This article is written by

    Mr. Goutham Rathinam

    (BE-Mechanical & CSWIP 3.1-TWI,UK)             

    Email ID: goutham.r86@gmail.com

     

  • Gate Valves – What is a Valve (Part – 3)

    Gate Valves – What is a Valve (Part – 3)

    In the Valves Part-1, you learned What is a valve, its history, and its categorization (Click here to read).

    In Part-2, you learned about the Globe valve. (Click here to read)

    In this, you are going to learn about Gate Valves categorized by design.

    Gate Valves:

    Gate Valve is a multi-turn valve that has a gate-like disc and two seats to close the valve. The gate moves linearly, perpendicular to the direction of flow. This type of valve is normally used in the fully opened or fully closed position; it is not suited to throttling applications. Gate valves provide robust sealing and are used extensively in the petrochemical industries.

    The basic construction of the Gate valve consists of Body, Bonnet, Seat, Disc, Stem & Handle.

    The body is the main pressure containing the structure of the valve and contains the valve’s internal parts that come in contact with the working fluid.

    Bonnet provides a leakproof closure for the valve body.

    The seat ring provides uniform leakproof tightness. Usually beveled to allow guiding during the final stage of closing.

    Disk or Wedge are closure member of the valve rests on the seat ring, connected to the stem which slides or screwed up or down to throttle the flow using a Handle.

    The stem connects the actuator/handle to the inside of the valve (disc) and transmits the actuation force. Stems are either smooth for actuator-controlled valves or threaded for manual valves.

    There are four primary Disc designs for Gate valves, namely: Wedge, Knife, Parallel slide & Slab Type.

     

    Wedge Gate Valves

    wedge type gate valve

    Wedge Gate Valves are commonly used in industrial piping for a stop or isolating – to turn on and shut off the flow as opposed to regulating flow. Gate valves are named from the gate-like disc which operates at a right angle to the path of the flow. Gate valves are general service valves that can be made in a broad spectrum of sizes using a variety of different materials. Wedge gate valves are metal seated but are also available with resilient seat insert if drip tight shut off is required. They can meet the demands of a wide range of pressure and temperature conditions and is available in full port. Advantages – a low-pressure drop, straight through flow either direction. Disadvantages – slow-acting, bulky. Not drip tight shut off (over 150NB). Do not partially open as this will cause damage to seat/disc.

     

    Knife Gate Valves

    knife edge gate valve

    Knife Gate Valves are used for many applications in larger sized pipework (50mm & above). Unlike traditional gate valves, they can throttle (at lower pressures) depending on online media and degree of opening. Metal seated knife gate valves are not leak tight shut-off. Some knife gate valves have a resilient seat in order to ensure they close drip-tight. Available in v-port, o-port, and lined they are ideally suited for the control of effluent, slurries, waste products, semi-solids, pulp, bulk powders. Most knife gate valves are designed for a single flow direction.

     

    Parallel Slide Gate Valves

    parallel slide valve

    Parallel Slide Gate Valves are popular in steam applications as the energized disc design handles thermal expansion without sticking like wedge gate valves. Another advantage is lower torque then wedge gate valves especially in venturi (Ferranti) reduced bores configuration. Parallel slide valves consist of two parallel gates that are always energized against the seat by springs or a wedging spreader bar between the two gates. No mechanical stress is exerted between the discs, and the valve is not subjected to dangerous strains in opening and closing. This design of the valve maintains fluid-tightness without the aid of wedging action. These valves are used for saturated and super-heated steam.

     

    Pipeline Slab Gate Valves

    slab gate valve

    Pipeline Slab Gate Valves are available in parallel solid slab and expanding 2-piece wedging slab. Both styles protect the seat area from the flow in all operating positions. These valves have a full through conduit configuration with a hole in the slab. Slab style gate valves have seats that are spring energized. The expanding slab features two opposed sliding V-shape segments that maintain pressure against the seats. These valves are for API 6D pipeline applications but are also used for API 6A wellhead valves. All these valves are made in metal to metal and soft seat configuration.

     

    This article is written by

    Mr. Goutham Rathinam

    (BE-Mechanical & CSWIP 3.1-TWI, UK)             

    Email ID: goutham.r86@gmail.com

  • Basics of Heat Treatment for Metallic Material (Part-1)

    Basics of Heat Treatment for Metallic Material (Part-1)

    Scope:

    In this article fundamentals of heat treatment will be discussed briefly mainly related to the “base material” of welded construction (metallic material) meant for industrial application.

    In Part-0, we had discussed the basics from a theory point of view generally taught in engineering colleges (Click here to read Part – 0).

    In the present article i.e Part – 1, we will discuss heat treatment from the industrial application point of view mainly for the materials to be joined by welding (Base materials).

    Importance of Heat Treatment: 

    Properties of steel can be changed considerably through heat treatment in its solid-state, at a specified chemical composition. The reason for this is the capability of the great majority of iron-carbon alloys to be transformed into polymorphous lattice formations.

    Need for Heat Treatment in welded Structure (to name a few) :

    1. To relieve the residual stresses (ferritic steels).
    2. To dissolve the carbides (chromium carbides) to avoid sensitization (intergranular corrosion) especially in austenitic steel.
    3. To make the microstructure of the steel especially low and high alloy steel (Cr-Mo, 13Cr-4Ni, etc.) suitable for service (tempered martensite).

    Heat Treatment based on when it is performed:

    1. Intermediate Heat Treatment: During cold forming or for high restraint joints in Cr-Mo Steel (Nozzle to Shell/Dish end joint).
    2. Post Weld Heat Treatment: Performed immediately after or after allowing the weldment to cool to room temperature with an aim as mentioned in the above points.

    Classification of Heat Treatment Process (Base Material):

    1. Annealing
    2. Hardening and
    3. Quenching/Tempering.

    Referring to figure 1 of Article-0 below features the characteristic temperature ranges for important heat treatment processes in the Fe-FeC system. It is evident that the heat treatment temperature is often dependent on the carbon content.

    Where;

    A1= The temperature at which austenite beings to form during heating,

    A3= The temperature at which the transformation of ferrite to austenite is complete during heating.

    Annealing: It’s a general term denoting a thermal treatment that consists of heating at a specific rate, holding at a specific temperature for a finite period of time and cooling at a specified rate primarily to soften the metallic materials.

    Homogenization Annealing fig 2

     

    Above figure-2 shows an example of Annealing (Homogenizing)

    Here:

    A1 = the temperature at which austenite beings to form during heating

    A3 = the temperature at which the transformation of ferrite to austenite is completed during heating.

    There are many types of annealing depending on the changes in material properties desired namely:

    • Achieving uniform microstructure:
      • Diffusion annealing
      • Normal annealing
    • To enhance workability
      • Coarse grain annealing
      • Soft annealing
      • Recrystallization annealing
      • Crystal recovery annealing
    • Minimizing the stresses
      • Stress relief annealing
      • Stress-relieving treatment
    • Microstructural changes
      • Tempering
    • Special Cases
      • Controlled Cooling
        • Quenching
        • Perlitic annealing
        • Bainitic microstructure transformation

    Normalizing: Heating to 30 to 50°K above A3 (austenising) temperature in case of hypoeutectoid (carbon steel) steel. The soaking time at hold temperature will be such that the whole job is heated uniformly to the normalizing temperature. After that, it will be cooled in the resting air.

    The aim of normalizing is thus also to achieve an even microstructure with fine lamellar pearlite.

    Normalizing

     

    • Above figure-3 represents a normalizing cycle.
    • Normalizing is recommended in the following cases:
      • In case of coarse grain.
      • In the case of solidification microstructure, eg weld joint or cast steel
      • In the case of steels embrittled due to aging and
      • In the case of all constructional steels with an insufficient toughness or too low a yield point.

    Stress Relief annealing: Heating to and holding at annealing below A1 with subsequent slow cooling, so that internal stresses are reduced without significant changes to the other properties

    Stress Relief annealing

    • Above figure-4 represents a stress relief annealing cycle.
    • Internal stresses can be generated due to uneven heating and cooling of the material e.g. during welding, soldering, solidification, or quenching but also due to cold forming. These stresses often cause distortion or lead to the formation of cracks in the component.

    Coarse grain annealing: it is carried out in the temperature range of 950° and 1100° C (above A3) with the hold time of about 1hr to 4 hr (Prolonged period of time) and cooling slowly to achieve coarse grain structure.

    The aim of coarse grain formation is to produce a coarse grain with low hardness and toughness. This type of microstructure is advantageous for milling, since the chips produced are small, thus leading to lower cutting forces.

    Coarse Grain annealing

     

    • Above figure-5 represents a coarse grain annealing cycle.

    Soft annealing (annealing on globular cementite): It is meant to reduce the hardness of the material to a defined value in which annealing is performed at temperature closely below or just above A1or held around A1 with subsequent slow cooling.

    • The aim of soft annealing is to obtain a soft microstructure suitable for further processing, such as milling or cold deformation.
    • The optimum condition of the microstructure consists of homogeneously distributed, fine-grained, globular carbides embedded in a ferritic matrix and such a microstructure can be split, bent, compressed, flanged, extruded or twisted with ease.
    • Below figure-6 represents the soft annealing cycle of low carbon steel.

    Single Soft Annealing of Steels with low carbon content

     

    Intensive Program Annealing

    • The above figure-7 represents heat treatment (2nd picture) which is mainly used in steels with carbon content above 0.5%, for example, with roller bearing steels.

     

    Diffusion annealing: Annealing in the temperature range of 1050°C to 1250°C, with a prolonged hold time of around 50hr, in order to balance local differences in the chemical composition due to segregation by diffusion.

    • Due to high temperatures during diffusion annealing a formation of coarse grains is unavoidable. Coarse grain can be removed by normalizing.
    • Below figure-8 represents a diffusion annealing cycle.

    Diffusion Annealing

     

    Recrystallization annealing: Heat treatment to realize new grain formation in a cold-formed workpiece through nucleation and growth without a phase change.

    • During cold forming as the hardness increases which reduces the formability and for this reason, cold deformation cannot be carried out indefinitely and hence after certain deformation recrystallization annealing in order to restore the original material properties.
    • Min recrystallization temperature = 0.4 times absolute melting temperature.
    • Three Stages involved are as mentioned below:
      • Crystal Recovery: It involves rectifying dimensional lattice structure imperfections and rearranging dislocations.
      • Primary recrystallization: It leads to complete grain reforming.
      • Secondary recrystallization: Above the recrystallization temperature, the small grains formed by primary recrystallization combine to form a small number of large grains.

    Recrystallization annealing

    • Above figure-9 represents a recrystallization annealing cycle.

     

    Solution annealing: The main aim of solution annealing is to bring and hold separated microstructures in solution (homogenizing).

    • This is particularly desirable with austenitic Cr-Ni steels (above 1000 C) because it enables the required corrosion resistance to be achieved.
    • The purpose is to obtain a standardized austenite crystal deprived of precipitations by rapidly cooling in chilled/room temperature water.
    • Above figure-10 represents a solution annealing cycle.

    Solution Annealing

     

    (Note: The purpose of this article is to give a general guideline to the readers, and it shall not be considered as a substitute for code. For full terms and conditions please read relevant code and its clauses).

     

    This article is written by;

    MR. SANDEEP SINGH PARMAR

    (Ex. GE, ISGEC & ESSAR)

    Email: sandeepparmar99@yahoo.com

    IWE (IN/IWE/41700026); B Tech (Mechanical); AMIIW (Welding Technology)

    ISO 9001:2008 Internal Auditor; ISO 9001:2015 Lead Auditor ;

    NDE L-II (UT, LPT, MPI, RT); Lean Six Sigma Green Belt;

    MWeldl IEng; MIE C Eng(Ind) ; M.I.Inst.W ; LM IIM

  • Basics of Heat Treatment (Part-0)

    Basics of Heat Treatment (Part-0)

    Scope:

    In this article, fundamental concepts of heat treatment will be discussed to give an overview to the reader with no previous knowledge of heat treatment processes.

    Why Part-0:

    Well, the readers might be wondering why this part or rather an article has been named as zero. Just like the thermodynamics (the study of particles in motion by virtue of its temperature) has four laws the first being zeroth law and the last being third law, the author follows the same methodology to cover the basics of heat treatment in four parts.

    Definition:

    Heat treatment definition

    Classification of Heat Treatment Process:

    1. Annealing
      1. Stress-relief annealing
      2. Process annealing
      3. Spheroidising (annealing)
      4. Full annealing
    2. Normalizing
    3. Hardening (by quenching)
    4. Tempering
    5. Martempering
    6. Austempering and
    7. Maraging

    Purpose of heat treatment:

    • Cause relief of internal stresses
    • Harden and Strengthen metals
    • Improve machinability
    • Change grain size
    • Soften metals for further working
    • Improve ductility and toughness
    • Increase, heat, wear and corrosion resistance
    • Improve electrical and magnetic properties (Note – 1)
    • Spheroidize tiny particles by diffusion (Note – 2)

    Note – 1: Very limited information available generally applicable to heat-treatable precipitation-hardened aluminum alloys

    Note – 2: Here annealing through diffusion is employed to remove any structural non-uniformity like dendrite, columnar grains, and chemical inhomogeneity which promote brittleness, reduce ductility and toughness of steel.

     

    Principle of Heat Treatment:

    • Made possible through eutectoid reaction [it is an isothermal reversible reaction in which a solid phase {austenite} is converted into two {pearlite-ferrite + cementite} or more intimately mixed solids on cooling, the eutectoid temperature is 723° C] of steel in the iron-carbon system (figure 1 below shows the eutectic point).

    Iron Carbon Diagram

    • Heat treatment of steel involves the transformation or decomposition of austenite.
    • The transformed product develops a range of useful physical and mechanical properties.
    • The cooling rate dictates whether transformation from austenite will yield perlite or martensite.
    • For heat treatment to be effective one of the elements should be soluble in the other in a solid-state (alloys) in different amounts under different circumstances.
    • The theory of heat treatment is based around the principle that an alloy experiences change in microstructure when heated above a certain temperature and it undergoes again a change in microstructure when cooled to room temperature.
    • Slow cooling above a critical range will produce Perlitic microstructure
    • Fast cooling will give rise to martensitic microstructure

     

    Stages of Heat Treatment Processes:

      • Heating a metal or alloy to definite temperature.
      • Holding at that temperature for a sufficient period to allow the necessary changes to occur.
      • Cooling at a rate necessary to obtain desired properties with changes in nature, form, size, and distribution of micro constituents.

     

    1. Annealing:

    • Definition: It is a process of heating a metal in which is in a metastable state, to a temperature, which will remove the instability, and then on cooling is so that the room temperature structure is stable.
    • Purpose:
      • Making the microstructure stable (full annealing)
      • Refining and homogenizing microstructure
      • Reducing hardness
      • Improving machinability, cold working characteristics, mechanical, physical, electrical and magnetic properties
      • Removing residual stresses and gases
      • Producing desired microstructure

     

    a. Stress Relieving (Recovery):

    • It relieves stresses produced by casting, quenching, machining, cold working, welding, etc.. It applies equally to ferrous and nonferrous materials.
    • It’s often desirable when casting is liable to change dimensions to a harmful degree during machining or use. The stresses if unrelieved may cause warpage or even failure of the casting.
    • Thermal stress relieving requires heating the casting to a temperature at which the relaxation of the elastic stress is brought about by the plastic deformation to the elastic strain.
    • It does not affect the metallurgical structure of the casting but essentially is one creep; the temperature required for SR is 0.3 to 0.4 times the melting point of the cast metal or alloy.

     

    b. Process Annealing(Subcritical):

    • Usually applied to counter the effects of cold working, to soften and permit further cold work as in weld wire drawing.
    • The ferrous alloys are heated below the lower transformation temperature range (550-650° C), are held at that temperature, and then cooled in air.
    • It is associated with only partial crystallization of the distorted ferrite.
    • It does not involve any phase change and the constituent’s ferrite and cementite remain present in the structure throughout the process.
    • Figure 2 below shows various heat treating processes.

    Heat treating temperatures in steel

    c. Spheroidise Annealing:

    *In this type the steel is subjected to a selected temperature, usually within or near the transformation range to produce a spheroidal or globular form of

    carbide in steel. Refer below figure;

    Spheroidizing

    • Purpose:
    1. Improves machinability and surface finish during machining
    2. Facilitates subsequent cold working operation
    3. Soften tool steel and some of the air-hardening alloy steels
    4. Prevents cracking of steel during cold forming operations
    • A spheroidized steel has a lower hardness and tensile strength & a correspondingly higher relative elongation and reduction of the area than steel subjected to normal annealing. (Temp range: 650-700° C).

    d. Full Annealing:

    • Annealing a ferrous alloy by austenitizing and then cooling slowly through the transformation range.
    • The austenitizing temperature for hypo eutectoid steels is usually between 723° C and 910° C; and for hypereutectoid steels, the austenitizing temperature in between 723° C and 1130° C (Refer figure 1 above).
    • It thus involves:
    1. Heating steel to proper annealing temperature in the austenitic zone;
    2. Holding the steel object at that temperature for a definite time depending upon its thickness or diameter (about 2.5 to 3 min /mm thickness) so that it becomes completely austenitic; and then
    3. Cooling very slowly the steel object through the transformation range,
    4. Preferably in the furnace or in any good heat-insulating material, till the object acquires a low temperature.
    • Slow cooling associated with full annealing enables the austenite to decompose at low degrees of supercooling to form

    A pearlite + ferrite structure in hypo eutectoid steels;

    A pearlite + cementite structure in hypereutectoid steels

    • Purpose:
    1. Refine grains
    2. Remove strains
    3. Improve- softness, machinability, formability, electrical and magnetic properties

     

    2. Normalizing:

    It consists of heating steel to about 40-50° C above its upper critical temperature and, if necessary, holding it to that temperature for a short time and then cooling air at room temperature.

    The type of structure obtained by normalizing will depend largely on the thickness of the cross-section as this will affect the rate of cooling.

    Normalizing produce microstructure consisting of ferrite and pearlite for hypo eutectoid steels.

    For eutectoid steels, the microstructure is only pearlite and it is pearlite and cementite for hypo eutectoid steels.

     

    • Purpose:
    1. Produces a uniform structure
    2. Refines grain size of steel, which coarsen during rolling and forging.
    3. Reduce internal stresses
    4. Eliminates the carbide network at grain boundaries of hypereutectoid steels

     

    3. Hardening by quenching :

    It is that heat treatment of steel which increases its hardness by quenching (and tempering).

    The maximum % increase of hardness by quenching is obtained if they contain between 0.35% and 0.60% carbon.

     

    • Purpose:
    1. Hardens steel to resist wear
    2. Enables steel to cut other metals
    3. Improves strength, toughness, and ductility
    4. Develops the best combination of strength and notch-ductility

    In this type steel with sufficient carbon (0.35% to 0.70%) is heated 30°- 50° C above A3 line, held at that temperature from 15-30 minute per 25 mm of cross-section and then cooled rapidly or quenched in a suitable medium to produce the desired rate of cooling and hardened steel.

     

    4. Tempering:

    Quench hardening produces martensite and retained austenite, the martensite formed is very hard and brittle; which may lead to cracks and distortion rendering the untempered steel useless for service.

    Also, the retained austenite is an unstable phase and as it changes with time, dimensions may alter. So it is necessary to temper the steel after quenching below the lower critical temperature (A1).

     

    • Requirements of Tempering:
    1. Heating hardened steel below A1 (lower critical temperature)
    2. Holding for 3-5 minutes for each mm of thickness/diameter.
    3. Cooling the steel either fast or slowly except in case of steels susceptible to temper brittleness.

    Essentially the tempering reaction can be thought of as the change from carbon atoms dispersed in the martensite to precipitated carbides particles of increasing size.

     

    • Purpose:
    1. Relieve residual stresses
    2. Improve ductility and toughness
    3. Increase % elongation

    The figure below shows a typical quench and tempering cycle:

     

    Quench hardening and tempering

    Classification of tempering:

    1. Low-temperature tempering:
    • It is carried out in a temperature range of 150 to 250° C.
    • Internal stresses are reduced, toughness, and ductility improved without affecting hardness.
    • The structure is martensitic.
    • It is applied to cutting tools of carbon steels, low alloy steels, and for surface hardening and carburization.

     

    1. Medium temperature tempering:
    • It is carried out in a temperature range of 350 to 450° C.
    • Develops a troostite structure.
    • Hardness and strength decrease while % elongation and ductility increase.
    • It imparts steel with the highest elastic limit with sufficient toughness.
    • Applied to coil springs, laminated springs, hammers, chisels, etc.

     

    1. High-temperature tempering:
    • It is carried out in a temperature range of 500 to 650° C.
    • Develops a sorbite structure.
    • Eliminates internal stresses completely.
    • It imparts high ductility in conjunction with adequate hardness.
    • Applied to connecting rods, shafts, gears, etc.

     

    5. Martempering:

    Heated above the critical range to make it all austenite, then quenched into a salt bath maintained at a temperature above the Ms and is held at this temperature long enough until the temperature is uniform across the section of the workpiece without transformation to austenite and subsequently cooling the workpiece in air through the martensite range, in turn resulting in martensite with a minimum of stresses, distortion and cracking which can be further tempered to increase ductility.

    In practice, to utilize benefits of martempering, alloying elements are added to steel. Otherwise, the critical cooling rate is too fast and the benefits of the martensite hardness cannot be realized in parts that are large or even medium in size.

    Refer below the figure for martempering and Austempering;

     

    Austempering & Martempering

    6. Austempering:

    • It consists of heating the steel above critical range to make all austenite, then quenching at a critical cooling rate into a salt bath or lead bath held in bainite range (205 to 425° C), the steel piece remains in the bath until the austenite is completely transformed into bainite and then it is allowed to cool to room temperature, the rate being immaterial.
    • It is a type of interrupted quenching that forms bainite instead of martensite.
    • The steels formed are tougher and more ductile than the steel of tempered martensite having equal hardness and tensile strength.
    • The major limitation being restriction in size to relatively thin sections so that the entire piece can quickly attain the temperature of a quenching bath.
    • For steels of higher hardenability, larger sections can be used.
    • Greater ductility and toughness along with high hardness.
    • Less distortion and danger of quenching cracks.

     

    7. Maraging (Martensitic + Aging):

    • Maraging steels obtain high strength and ductility by combining a martensitic type of hardening of a basic iron-nickel alloy with age hardening of the martensite.
    • In other words, these steels attain ultra-high-strength on being aged in martensitic conditions. (E.g. 18Ni Marage 250).
    • The precipitation within the martensite is produced by tempering for 3 hr. at 480° C to obtain high notched toughness and ultra-high tensile properties.

    Applications:

    Rocket and missile cases, aircraft structural parts, mortar and rifle tubing, hot extrusion dies, etc.

    They possess the following properties:
    1. Strength, ductility, and toughness
    2. Freedom from distortion
    3. Good machinability
    4. Good weldability

     (Note: The purpose of this article is to give a general guideline to the readers, and it shall not be considered as a substitute for code. For full terms and conditions please read relevant code and its clauses).

     

    This article is written by;

    MR. SANDEEP SINGH PARMAR

    (Ex. GE, ISGEC & ESSAR)

    Email: sandeepparmar99@yahoo.com

    IWE (IN/IWE/41700026); B Tech (Mechanical); AMIIW (Welding Technology)

    ISO 9001:2008 Internal Auditor; ISO 9001:2015 Lead Auditor ;

    NDE L-II (UT, LPT, MPI, RT); Lean Six Sigma Green Belt;

    MWeldl IEng; MIE C Eng(Ind) ; M.I.Inst.W ; LM IIM

  • How to select welding electrodes

    How to select welding electrodes

    The selection of right welding electrodes is a quite challenging job because we need to consider many factors while choosing the best alternative. In this article, we will discuss the various factors responsible for choosing the right welding electrode for the Shielded Metal Arc welding Process (SMAW) for Carbon steels. The Shielded metal arc welding electrodes are always covered by flux and the electrode’s name starts with E followed by either a four-digit number or a five-digit number for example E7018, E6010, E6013, E10018, etc.

    Each letter and digit has a specific meaning, for example: in E7018 the letter ‘E’ stands for Electrode, ‘70’ denotes the minimum tensile strength i.e. 70 Ksi (or 70000 Psi) for this case, the second last digit i.e. ‘1’ indicates the position in which the electrode can be used. In particular, the letter ‘1’ depicts all position and the last two digits together shows the polarity and the flux composition of the electrode. To read more about the electrode symbols and their meaning please read this article: https://www.weldingandndt.com/welding-electrodes-understanding-the-electrode-symbols/

    As discussed earlier, we need to consider various factors before choosing an electrode. These factors are as under;

    1. Base metal or Parent Metal

    2. Welding Position

    3. Power Supply

    4. Joint Preparation

    5. Welding Quality/Weld finish

    6. Welding Cost

    We will discuss these factors one by one. Please note that a selection chart for choosing the correct welding electrode based on the parent material (in PDF format) is given at the end of this article.

    1. Base Metal or Parent Metal: Base Metal or Parent Metal is one of the most important factors to be considered while selecting an electrode. We need to take into consideration three following parameters;

    a. Base metal mechanical properties: The mechanical properties especially the tensile strength of the electrode and that of the base metal should be similar or as close as possible. In case of wide differences in tensile strength between the welding electrode and the base metal, there will always be chances of cracking and other welding discontinuities. Hence to prevent cracking and other welding discontinuities we should always choose an electrode having minimum tensile strength equivalent to the parent metal being welded.

    b. Base metal chemical properties: The chemical properties shall also be checked before choosing an electrode. The chemical composition of the electrode should match the chemical composition of the base metal, especially the carbon percentage. However, practically it’s not possible to match every parameter of an electrode with the base metal. Hence we need to choose an electrode having chemical properties as close as possible with the parent metal.

    c. Base metal thickness: Base metal thickness is very important while choosing an electrode. For thinner materials, an electrode with soft arc and less penetrating power can give good results but for thicker material we need and electrode with digging arc for deep penetration, maximum ductility, and low hydrogen for defect-free welding.

    We should always keep in mind that the electrode size (diameter) should not be more than the thickness of the parent metal.

    2. Welding Position: The second factor is the welding position. Each electrode is meant for welding at some particular position. Hence we need to choose electrode as per the position of our job. The welding position is specified in the electrode name itself i.e the second last digit gives the position for example: in the E7018 electrode, the second last digit i.e. 1 give the position for which the electrode can be used. A general summary of the welding position for electrodes are given below (Table 1);

    Table 1

    Welding electrode position table
    Welding electrode position table for selection of an electrode

    3. Power Supply: Some electrodes can be used with alternating Power (AC) supply, some can be used with direct current power (DC) supply and Some electrodes work well with both AC as well as DC. Hence, depending upon the power output of the welding machine we can choose the electrode. For example, if the machine is capable of giving only AC output, then we will not be able to use the electrodes which are not meant for AC. However, if the welding machine is capable of both AC as well as DC output then we can choose from a broader range of electrodes.

    When using Direct Current (DC) power supply, if the electrode is connected with the positive terminal of the machine then it is known as Direct current electrode positive (DCEP) or reverse polarity and, if the electrode is connected with the negative terminal of the machine then it is known as Direct current electrode negative (DCEN) or straight polarity. DCEP is the preferred polarity for most of the Shielded metal arc welding (SMAW) operations. However please refer to Table-2 for the correct polarity in which welding electrodes can be used.

    The last two digits of the electrode name denotes the polarity as well as the flux of the electrode. Please see the table given below (Table 2) for a summary of electrodes and the polarity in which they can be used.

    Table 2

    polarity of arc welding electrodes
    Table for the polarity of arc welding electrodes, to be considered while choosing an electrode

    4. Joint Preparation: The fourth factor to be considered while selecting an electrode is the joint preparation or groove configuration. It there is a tight fit-up or unbevelled root face then an electrode with a digging arc can be used, which can provide deeper penetration. Electrodes such as E6010 or E6011 can be used for this purpose. If there is sufficient root gap and beveled root face, then we can use electrodes which can give shallow to moderate penetration such as E6013 or E7018.

    Depending upon the operating characteristics, Grouping of SMAW electrodes can be done in the following ways;

    1. Fast-Freeze electrodes
    2. Fast-Fill electrodes
    3. Fill-Freeze electrodes
    4. Low Hydrogen electrodes

    Fast-Freeze electrodes (EXX10/EXX11) are those which can solidify quickly and are capable of giving forceful arc which helps in deep penetration and slag formation is quite low. Whereas The Fast-Fill electrodes (EXX22/EXX24/EXX24/EXX27/EXX28) can be melted very quickly with a high deposition rate and travel speed is also very high. However, these electrodes produce heavy slag.

    The third type of electrodes i.e. Fill-Freeze electrodes (EXX12/EXX13/EXX14) is a compromise between the fast-freeze electrodes and fast-fill electrodes, hence the Fill-Freeze electrodes possess characteristics in-between the Fast-fill and the Fast freeze electrodes. These electrodes are having medium penetration and medium deposition rate hence very useful for Thin/Sheet metal welding.

    The fourth type of electrodes is Low Hydrogen Electrodes (EXX15/EXX16/EXX18). Some Low Hydrogen Electrodes are having characteristics similar to fast-fill and some are having similar to Fill-Freeze. But they have been grouped separately because of their Low Hydrogen properties. These electrodes produce excellent welding with high ductility and good notch toughness.

    In case of a low diameter pipe, back-chipping and welding from the other side (ID side) can,t be done due to inaccessibility, hence a deeper penetration is always required. Hence we can select Fast-Freeze electrodes like E6010 for that case. To weld Sheet Metal or material with very low thickness, we can choose Fill-Freeze electrodes like E6013, because of it’s medium penetration characteristics. Hence Selection of electrodes can be done in this way too.

    5. Welding Quality/Weld finish: The required quality and the weld finishing is also an important factor to be considered before selecting an electrode. Electrodes can be chosen depending upon the final finishing requirement for example Flat weld bead, concave weld bead, or convex weld bead. The quality of the weld must suit the service requirements of the job. For example, to weld cryogenic vessel parts that are supposed to work at very extreme temperature and pressure with high impact loading or parts that are subjected to a corrosive atmosphere, we need a low hydrogen electrode such as E7018, which can produce very sound welding with higher ductility. So the chances of getting any weld defect during operation will be minimized. Table 3 gives a summary of the features of welding electrodes, which you may find useful while selecting an electrode for a particular job.

    Table 3

    Electrode selection criteria

    6. Welding Cost: Finally, the cost of the electrode should be considered according to your project requirement. We cannot choose a costly electrode for a low budget project. Similarly, for critical jobs where quality needs to be given utmost care a low hydrogen electrode with higher ductility such as E7018 can be considered to meet the quality requirements.

    Hence, While selecting the welding electrodes the above factors can be considered to get the required result.

    To download the Welding electrode selection chart/guide according to the base metal (in pdf format), please click on the below link;

    Electrode Selection guide as per parent metal
  • How To Make Weld Map, Shop Weld Plan, WPS, PQR & WPQ for A Static Pressure Vessel (Part-3)

    How To Make Weld Map, Shop Weld Plan, WPS, PQR & WPQ for A Static Pressure Vessel (Part-3)

    Scope:

    In part-2, of this article, we had discussed the sequence to be used for qualification of procedure (PQR) which needs to be approved by customer/client/TPI. (Please click here to read that article)

    Now we shall proceed for performance (welder) qualification i.e Welder performance qualification – WPQ or welder qualification test – WQT (which will be discussed in brief as the steps are identical to PQR qualification). This discussion shall be as per the proposed list mentioned in Part-1 (Click to see). We will see the weld map preparation again for final customer approval and issues of the shop weld plan to the shop for fabrication.

    The general steps for welder performance qualification (WPQ or WQT) are as mentioned below (Please note that these steps are not mandatory and vary for each and every case);

    (Based on PQR qualified (let us assume that all the testing got cleared and PQR was signed in article-2 by the concerned). WPS’s shall be prepared on basis of above qualified PQR’s for use in the Static pressure vessel fabrication and qualification of WPQ.)

    Step 1:

    The WPS along with test certificates of base metal, filler metal, and machine (welding power source) calibration report to be used for WPQ shall be offered to TPI.

    In most of the cases, the customer specifications demand the WPQ to be witnessed by TPI (Lloyds, BV, TUV, HSB, etc..) also the welding engineer shall in each case qualify a WPQ under TPI’s only so as to show the credibility of the same to future clients.

    Step 2:

    Now at this stage generally the TPI will just review the TC (considering he/she has enough confidence in our QMS system). All the test coupons (pipes) on both sides of the hard stamp of the TPI will be taken. The pipe shall have a width of at least 150 mm so can it be used repeatedly along with appropriate circumference (for either RT/UT or mechanical testing – at least 150 mm recommended) and the thicknesses as mentioned in the proposed WPQ (Recommendation based on the Author experience not to be constituted as mandatory).

    Step 3:

    Before setup of the test coupon, LPT examination of the edges may be performed so as to ascertain no surface defects are present. Now the qualification of test coupon shall be in vertical up position, as it will qualify the procedure in all positions with/without impact test requirements. The Included Angle, Bevel Angle, Root Face, and Root Gap, etc.  can be verified using the following instruments;

    • Vernier Caliper – Photo 1
    • Angle (Bevel Protector) – Photo 2
    • Bridge Cam (Universal) Welding Gauge – Photo 3
    • Hi-lo Gauge

    Photo 1

    Digital Vernier Caliper

    Photo 2

    Bevel (Angle) protector

    Photo 3

    Universal welding gauge

    Step 4:

    Now the edge preparation shall be done by gas cutting (however machining can also be used) but it will be recommended to use the edge preparation method same as that to be utilized in actual fabrication (however this is not an essential variable). Pipe fixture (Photo – 4) can be used pipe alignment.

    Photo 4

    pipe fixture

    For setup of pipe fixture as mentioned below (Photo – 5) can be used for proper alignment (C cleats can also be used @ 120° apart) and uniform root gap. While keeping the fixture in place and filler wire inserted in form of U to maintain the uniformity of root gap 3 tack welds of 10 mm length each as 120° to be made and afterward the fixture can be removed.

    Photo 5

    pipe fixture for alignment

    Note:

    1. Fixtures shall not be used as a lifting device in any case.
    2. For SMAW WPQ either a single root run of GTAW or ceramic backing can be used.

    Step 5:

    The Edge preparation after cutting shall be ground smooth to base metal surface to remove any slag formed during the cutting operation. Schematic Sketch is shown below (Photo – 6):

    Photo 6

    Groove angle

    Step 6:

    Now the welders will be briefed about the task on hand as per qualified WPS (essential variables) and a piece of the plate will be used to set the current, voltage, travel speed and gas flow rate which will be measured appropriately by using the following instruments;

    • AC/DC Clamp meter – Photo 7
    • flow meter gauge – Photo 8
    • Vernier – Photo 2

    Photo 7

    AC/DC Clamp meter

    Photo 8

    flow meter gauge

    Step 7:

    Now the welder shall start welding (as per qualified WPS in 6G position) and at least one welding engineer/welding training in charge per test coupon shall be deputed to record the parameters on the parameter format (welder performance qualification parameter record sheet).

    In most of the cases, the root run is witnessed by the TPI and he/she signs the sheet and allows the rest of the welding but all the passes can be witnessed by the TPI (Refer 2nd page of the parameter sheet as mentioned in Serial No. 10).

    Step 8:

    All the parameters need to be recorded on the parameters sheet (as mentioned in serial no 10) and after completion of the test coupon welding, the parameter sheet shall be signed by Welding Engineer and TPI.

    Step 9:

    Pipes (Single Side Welded – GTAW & GTAW + SMAW process) are allowed to cool below 50° C and then perform LPT (Liquid penetrant test)

    Please click here to download sample WPS for GTAW process

    Please click here to download sample WPS for SMAW + GTAW process

    Step 10:

    After clearing LPT examination RT/UT or mechanical testing can be performed as per ASME SEC IX (for this case author will perform RT only).

    If there is any repair in the test coupon, the same shall be marked suitably and if the whole length of the test coupon is full of defects (Lack of Fusion, Inclusions, etc..) same shall be discarded and the welder stands disqualified and may be allowed to weld another test piece after appropriate retraining and if the test coupon clears either RT a report of the same shall be prepared by ASNT NDE L_II qualified personnel which later on will become part of the WPQ documentation.

    To understand more about acceptance criteria for Radiography Test (RT) of welder performance qualification test coupon (As per ASME BPVC Section IX), Please watch the following video;

    [embedyt] https://www.youtube.com/watch?v=jAtiB89AjHo[/embedyt]

    Step 11:

    Now supposing all the welders clear RT examination WPQ will be prepared for each welder and a welder id card will be issued detailing the essential variables as the welders will not be allowed to keep a copy of WPQ (opinion of the author only).

    Please click here to download the format for welder performance qualification in SMAW process

    Please click here to download the format for welder performance qualification in GTAW process

    Step 12:

    Now after completion of all qualified WPS, PQR and WPQ’s, the welding engineer shall now prepare weld map for fabrication approval of the customer/client/TPI and which may take the following form (Photo 9):

    Photo 9

    weld map

    Step 13:

    Now the Shop Weld Plan will be prepared in reference to the below-mentioned parts list: (please click here to download a sample weld plan, which we will use in our case).

    Step 14:

    The List of the Welders shall be amended now to show the qualification of the welders;

    Step 15:

    Now all the documents viz. Weld map, WPS, PQR, Qualified Welder List, and WPQ will be submitted for approval of the customer/client/TPI.

    Step 16:

    After approval, the Shop Weld Plan along with WPS and qualified welder list will be issued in Welding & NDT (Manufacturer of Static Pressure Vessel) shop for fabrication.

    Note: If there are any changes like the addition of deletion of seam no the same will need to be reflected in Shop Weld Plan and Weld map and those shall be then submitted in the final dossier (supposing that the deviation was approved beforehand).

    Feedback Review: One of our readers in article-1 asked whether or not plate qualifies for pipe as well for all diameters in case of procedure qualification.

    Reply: If anyone goes through the essential variables for SMAW & GTAW procedure qualification the diameter is not an essential variable and hence this provision in the code saves us from doing an extra procedure qualification for qualification of welders in 2” pipe (In our case Mr. Sandeep Singh with GTAW process).

    (Note: The purpose of this article is to give a general guideline to the readers and it shall not be considered as a substitute of code. For full terms and conditions please read ASME Section VIII DIV I 2019 & ASME SEC IX 2019 edition).

    This article is written and published by;

    MR. SANDEEP SINGH PARMAR

    (Ex. GE, ISGEC & ESSAR)

    Email: sandeepparmar99@yahoo.com

    IWE (IN/IWE/41700026); B Tech (Mechanical); AMIIW (Welding Technology)

    ISO 9001:2008 Internal Auditor; ISO 9001:2015 Lead Auditor ;

    NDE L-II (UT, LPT, MPI, RT); Lean Six Sigma Green Belt;

    MWeldl IEng; MIE C Eng(Ind) ; M.I.Inst.W ; LM IIM

  • Summary of ASME BPVC Section VIII Div 1 (Part 4)

    Summary of ASME BPVC Section VIII Div 1 (Part 4)

    In Part-3 of this article the Subsection A was covered from UG-36 up to UG-79, to read the Part-3 of this article please click here. 

    This article i.e. Part-4 will deal with the general requirements preceding from UG-80 onwards.

    Subsection A

    UG- 80: Ovality tolerances for cylindrical, conical and spherical pressure part shellsOvality tolerances for cylindrical and conical sectionsFor internal pressure the following formula shall be used:

    formula for ovality

    • External pressure shall meet the requirements as mentioned above for internal pressure and
    • Must meet the requirements of figure UG-80.1. For more details, Please refer code.

    (Please note that the design calculation won’t be dealt in detail, and the readers are advised to refer the code for their specific type of vessel design.)

    UG- 81: FORMED HEAD TOLERANCES

    Inner surface out of acceptance (specified shape) is 1.25% of D for tori spherical, tori conical, hemispherical or elliptical head and for acceptance inside the specified shape is 0.625% of D (Nominal inside Dia of pressure equipment). For more details, Pleasse refer code.

    UG- 82: LUNGS AND FITTING ATTACHMENTS

    All the internal and external attachment on the pressure equipment shall be so built-in so as to conform to the curvature of the shell or head to which they are attached.

    When a pressure parts (such as nozzle) and non-pressure parts (ex lugs) which are directly over another pressure part (Shell/head circ or long seam) then the pressure part (nozzle/lugs) seams shall be ground flush.

    For others openings, Please refer code.

    UG-83: HOLES FOR SCREW STAYS

    For details, Please refer code.

    UG-84: CHARPY IMPACT TESTS

    • This test is performed to check the brittleness (of a normally ductile material) tendency of material at low temperatures.
    • They are performed for the weldment (Weld & HAZ) and for the parent material.
    • The procedure followed is generally as mentioned in SA 370 (ASME SEC II Part A).
    • Suppose the Minimum Design Metal Temperature (MDMT) of the pressure equipment is
    •  -10°C so in no case the impact test temperature be -9°C but it can be less than -10°C (Say for example -11°C).
    • 3 samples shall constitute a set and as far as practicable the size of the specimen shall be 10x10x55 (mm) for plates of 11 mm thick or more and if thickness is less than 11 mm refer code for the specific dimensions and reduction in test temperature with a corresponding reduction in impact absorbed energy values from SA 370.
    • Impact test are not required if the max width along the notch of the specimen is less than 2.5 mm.

    Charpy V Notch 2 mm Impact test specimen size: 55(L) x10(W) x10(H)Charpy V Notch 2 mm Impact test specimen size: 55(L) x 10(W) x 10(H)

    • For detailed dimensions refer code the above figure is for general understanding only.
    • Retest: Say for example the average value required is 27 J and the single value permissible for single specimen is 20 J so  a retest ( additional set) is required under following conditions:
    1. Say the values is 22 J, 26 J and 40 J so the average is 29.3 J so two values are below the average hence a set shall be retested from the remaining test coupon with all the conditions same as for the original test.
    2. Say the values are 19 J, 30 J and 40 J so the average workout to be 29.6 J in which only one value is below single specimen minimum of 20 J and hence a set shall be retested from the remaining test coupon with all the conditions same as for the original test.
    • For above two conditions each and every retested sample from the set shall have absorbed impact energy equal to or greater than 27 J.
    • A separate article will cover the detailed impact test location (with sketch for each case such as single process, multiple process and different group no) for procedure qualification test coupon along with production test coupon.

    UG-85: HEAT TREATMENT

    If the heat treatment as per material specification (ex. plate) are not accomplished by the mill than the same may be accomplished under the control of the manufacturer (of pressure equipment) and shall be documented as mentioned in the code.

    INSPECTION & TESTS

    UG-90: General

    • The pressure equipment’s which require U or UM designator shall conform to the general rules of inspection and tests in addition to the necessities of subsection B & C of this code.
    • The manufacturer holding U or UM designator certification has the following responsibilities to fulfill the requirements:
    • Certification authorized by ASME.
    • The design calculations for pressure equipment and its parts along with obtaining of partial data reports.
    • Material used in construction of pressure equipment shall be duly recognized.
    • Examination (say Combination of UT, RT & LPT) to ascertain the thickness and to detect any defects and maintain traceability.
    • Documentation for the test carried out (ex: impact prod test).
    • Access for inspection to the inspector, prior approval of base metal repair procedures.
    • Availability of WPS, PQR, WPQ, WOPQ, QAP, ITP, and inspection test reports (set up, dimensional etc…) to the inspector and so on and so forth.
    • Please refer code for other details.

    UG-91: THE INSPECTOR

    • In this code inspector will always means an authorized inspector (abbreviated as AI) and will be employed by ASME Recognized agency like Lloyd’s, TUV, HSB etc…
    • Inspectors may be employed by the employer (Pressure equipment manufacturer) if the pressure equipment’s manufactured by the manufacturer is for his own use only, otherwise inspectors (AI) shall not be employed by pressure equipment manufacturer.
    • Inspector shall also monitor quality management system of the manufacturer.

    UG-92: ACCESS FOR INSPECTION

    • Without any hindrance the inspector shall be given access to the pressure equipment by the manufacturer weather at site or shop.
    • Inspector shall be notified of the progress of the pressure equipment and for any inspection shall be informed by the manufacturer well in advance.

    UG-93: INSPECTION OF MATERIALS

    • Material Test Reports (MTR) from material manufacture shall be available for evaluation to inspector.
    • It shall (MTR) shall document all the tests as required by the material specification and if some of the test are to be made latter proper documentation of the same to be kept.
    • For more details refer code.

    UG-94: MARKING ON MATERIALS

    • Inspector to check the marking on the parts of pressure equipment’s

    UG-95: EXAMINATION OF SURFACES DURING FABRICATION

    • To guarantee the material is free of any unwanted discontinuity and defects the examination of the surfaces shall be made.

    UG-96: DIMENSIONAL CHECK OF COMPONENTS PARTS

    • Manufacturer shall conform that the parts of pressure equipment’s conform to the shape (within tolerances) and the thickness of the components after forming.
    • Fitness with vessel curvature needs to be determined by the manufacturers for various attachments (Such as Nozzles etc…)
    • The Dimensional conformance to the code shall be determined by the inspector.

    UG-97: INSPECTION DURING FABRICATION

    • Before making a closing seam in the job a complete inspection of the pressure equipment shall be performed.
    • Before hydrostatic or pneumatic test inspector shall inspect the external surfaces of the pressure equipment’s.

    UG-98: MAXIMUM ALLOWABLE WORKING PRESSURE

    • Please Refer code for details

    UG-99: STANDARD HYDROSTATIC TEST

    • Hydrostatic pressure = 1.3 * maximum allowable working pressure (MAWP)
    • Please refer code for details

    (To learn more about Hydrotest, Please click here.)

    UG-100: PNEUMATIC TEST

    • Pneumatic test can be used instead of hydrostatic test when the design of the pressure equipment make it unsafe to fill it with water, the pressure equipment cannot be dried easily.
    • Pneumatic test pressure = 1.1* maximum allowable working pressure* lowest stress ratio
    • Where Stress Ratio =  Stress value at test temperature/Stress value at design temperature
    • To minimize the risk of inelastic fracture the temperature during the test shall be equal to or greater than 17°C above the minimum design metal temperature.
    • The increment in pressure shall be as mentioned in the code.
    • For rest of the details refer code.

    UG-101: PROOF TESTS TO ESTABLISH MAXIMUM ALLOWABLE WORKING PRESSURE

    For details refer the code.

    UG-102: TEST GAUGES

    For details refer the code.

    UG-103: NON DESTRUCTIVE EXAMINATION

    Magnetic Particle Inspection and Liquid Penetrant testing where ever referenced shall be performed as per ASME SEC V.

    MARKING AND REPORTS

    UG-115-116: GENERAL, REQUIRED MARKING

    Refer code for details

    UG-117: CERTIFICATE OF AUTHORIZATION AND CERTIFICATION MARKS

    Refer code for details

    UG-118: METHODS OF MARKING

    • By utilizing name plate, stamping on to the pressure equipment, electrochemically etched.
    • For more details refer code.

    UG-119: NAME PLATES

    Refer code for details

    UG-120: DATA REPORTS

    Refer code for details

    OVER PRESSURE PROTECTION

    • UG-125:  GENERAL
    • UG-126:  PRESSURE RELIEF VALVES
    • UG-127: NON RECLOSING PRESSURE RELIEF DEVICES
    • UG-128: LIQUID PRESSURE RELIEF VALVES
    • UG-129: MARKING
    • UG-130: CERTIFICATION MARK
    • UG-131: CERTIFICATION OF CAPACITY OF PRESSURE RELIEF DEVICES
    • UG-132: CERTIFICATION OF CAPACITY OF PRESSURE RELIEF VALVES IN COMBINATION WITH NOR RECLOSING PRESSURE RELIEF DEVICES
    • UG-133: DETERMINATION OF PRESSURE- RELIEVING REQUIREMENTS
    • UG-134: PRESSURE SETTING AND PERFORMANCE REQUIREMENTS
    • UG-135: INSTALLATION
    • UG-136: MINIMUM REQUIREMENTS FOR PRESSURE RELIEF VALVES
    • UG-137: MINIMUM REQUIREMENTS FOR RUPTURE DISK DEVICES
    • UG-138: MINIMUM REQUIREMENTS FOR PIN DEVICES
    • UG-140: OVER PRESSURE PROTECTION BY SYSTEM DESIGN
    • Refer code for Details

    (Note: Purpose of this article is to give a general guideline to the readers and it shall not be considered as a substitute of code. For full terms and conditions please read ASME Section VIII DIV I, 2017 edition).

    This article is written and published by;

    MR. SANDEEP SINGH PARMAR

    (Ex. GE, ISGEC & ESSAR)

    Email: sandeepparmar99@yahoo.com

    IWE (IN/IWE/41700026); B Tech (Mechanical); AMIIW (Welding Technology)

    ISO 9001:2008 Internal Auditor; ISO 9001:2015 Lead Auditor ;

    NDE L-II (UT, LPT, MPI, RT); Lean Six Sigma Green Belt;

    MWeldl IEng; MIE C Eng(Ind) ; M.I.Inst.W ; LM IIM

  • Globe Valves – What is a Valve (Part – 2)

    Globe Valves – What is a Valve (Part – 2)

    In the Valves Part-1, you learned, What is a valve, its history and its categorization, to read that article please click here.

    In this article, we will discuss about the valves categorized by design. The list follows as;

    • Globe Valve
    • Gate Valve
    • Plug Valve
    • Ball Valve
    • Butterfly Valve
    • Diaphragm Valve
    • Pinch Valve
    • Piston Valve
    • Needle Valve
    • Check Valve
    • Relief & safety Valve
    • Special Valve

    In particular, this article is going to speak about Globe valves. History of valves was already discussed in Part-1 (Please click here to read part 1 of this article).

    Globe Valves

    Globe valve is a Linear Motion type of valves and is typically used in both On-Off and Throttling applications. In globe valves, the flow of the fluid through valve follows an S-path. Due to this, the flow direction changes twice which results in higher pressure drops. Due to other advantages offered by them, they are widely used in applications where pressure drop through the valve is not a controlling factor.

    These valves are generally not used beyond sizes larger than DN 300 as enormous forces are exerted on the stem to open or close the valve under fluid pressures. Globe valves require high pressures on the seat to keep it closed when the fluid exerts pressure from the bottom of the disc.

    The basic construction of Globe valve consists of Body, Bonnet, Seat, Disc, Stem & Handle.

    Body is the main pressure containing structure of the valve and contains the valve’s internal parts that comes in contact with the working fluid.

    Bonnet provides a leakproof closure for the valve body.

    Seat ring provides uniform leak proof tightness. Usually bevelled to allow guiding during the final stage of closing.

    Disk are closure member of the valve rests on the seat ring, connected to the stem which slide or screwed up or down to throttle the flow using a Handle.

    Stem connects actuator/handle to the inside of the valve (disc) and transmits the actuation force. Stems are either smooth for actuator-controlled valves or threaded for manual valves.

    There are three primary body designs for Globe valves, namely:

    1. Tee Pattern or Z-body
    2. Angle Pattern
    3. Wye Pattern or Y-body

    1. Tee Pattern Globe valves: Tee Pattern Globe valves (Figure 1) are the most common body type, with a Z-shaped diaphragm. The horizontal setting of the seat allows the stem and disk to travel perpendicular to the horizontal line. This design has the lowest coefficient of flow and higher pressure drop. They are used in severe throttling services, such as in bypass lines around a control valve. Tee-pattern Globe valves may also be used in applications where pressure drop is not a concern and throttling are required.

    Figure 1 (Tee Pattern Globe valve)

    T pattern glove valve

    2. Angle Pattern Glove Valves: Angle Pattern Globe valves (Figure 2) are modified basic Tee Pattern Globe valve. The ends of this Globe valve are at an angle of 90 degrees, and fluid flow occurs with a single 90 degrees turn. They have a slightly lower coefficient of flow than wye-pattern Globe valves. They are used in applications that have periods of pulsating flow because of their capability to handle the slugging effect of this type of flow.

    Figure 2 (Angle Pattern Globe valve)

    Angle Pattern Globe Valve

    3. Wye Pattern Globe valves: Wye Pattern Globe valves (Figure 3) is an alternative for the high pressure drop, inherent in Globe valves. Seat and stem are angled at approximately 45 degrees, what gives a straighter flow path at full opening and offer the least resistance to flow. They can be cracked open for long periods without severe erosion. They are extensively used for throttling during seasonal or start-up operations. They can be rod through to remove debris when used in drain lines that are normally closed.

    Figure 3 (Wye Pattern Globe valve)

    wye pattern globe valve

     

    Click here to read the next part of this article.

     

    This article is written and published by

    Mr. Goutham Rathinam

    (BE-Mechanical, CSWIP 3.1-TWI,UK)             

    Email ID: goutham.r86@gmail.com

  • How To Make Weld Map, Shop Weld Plan, WPS, PQR & WPQ for A Static Pressure Vessel (Part-2)

    How To Make Weld Map, Shop Weld Plan, WPS, PQR & WPQ for A Static Pressure Vessel (Part-2)

    Scope:

    In part-1 (Click here to read), of this article, we had discussed about the preparation and approval of the weld map, shop weld plan, and proposed welder list which needs to be submitted for the consent of the customer/client/TPI.

    In this article, we shall discuss the steps required for PQR qualification. In general, the Steps as mentioned below may be followed (But not mandatory for each and every case) for PQR qualification:

    (Note: In most of the cases the customer specifications demand the PQR (procedure qualification record) to be witnessed by Third party inspection (TPI) agencies such as Lloyds, BV, TUV, HSB, etc.. The welding engineer, shall in each case, qualify a PQR in the presence of TPI’s only to show the credibility of the same to future clients.)

    The necessary steps required to be followed for PQR qualification are given below;

    Step 1:

    The Proposed WPS i.e PWPS, Filler Metal batch test certificate’s (SMAW Consumable & GTAW Consumable), Base Metal test certificate (For WPS & WPQ), machine calibration report (for constant current power source) shall be reviewed by welding engineer and TPI. Sample test certificate for the following materials can be downloaded;

    Step 2:

    Mostly the TPI will ask to witness the plate/pipe from which the test coupon will be removed and also to verify the Heat/Plate No as mentioned in the TC reviewed in step 1 (Figure 1). Also, it is essential in this step to take multiple stamps (TPI) on plate/pipe so that before cutting and if possible after machining the stamp transfer stages can be avoided which will unnecessarily prolong the PQR qualification process. The length of each test piece(plate) generally to be kept 500 mm and the width of each test piece shall be 150mm and the thicknesses as mentioned in the proposed WPS (Recommendation based on the Author experience not to be constituted as mandatory).

    Figure 1

    Heat number and part number SA516 Gr. 70 for PQR

    Step 3:

    Now the edge preparation shall be prepared by the gas cutting (however machining can also be used) but it will be recommended to use the edge preparation method the same as that to be utilized in actual fabrication (however this is not an essential variable). The Run in and run out cleats and the backing support to control angular distortion (Figure 2) shall also be cut from the material of the same plate however for backing a suitable fixture (Figure 3 and Figure 4) can be made to avoid cutting/grinding and localized repair of the base metal at the location from where supports will be removed after welding.

    Figure 2

    PQR test Coupon

     

    Figure 3

    Fixture for holding the pqr/welder test coupon

     

    Figure 4

    Welder test piece/pqr test coupon with fixture

     

    Step 4:

    The Edge preparation after cutting shall be ground smooth to base metal surface so as to remove any slag formed during the cutting operation. Schematic Sketch is shown below (Figure 5):

    Figure 5

    welder qualification/pqr test coupon

    Step 5:

    Before doing the setup, the LPT examination of the edges may be performed to ascertain no surface defects are present. Now the qualification of all three test procedures shall be in vertical up position as it will qualify the procedure in all position with/without impact test requirements verify: Included Angle/Bevel Angle, Root Face, and Root Gap, etc. using the following items;

    • Digital Vernier (Figure 6)
    • Angle Protector (Figure 7)
    • Universal Welding Gauge (Figure 8)
    Figure 6

    digital vernier caliper

     

    Figure 7

    digital bevel protractor

     

    Figure 8

    Universal welding gauge (bridge cam gauge)

     

    Step 6:

    Now the welders will be briefed about the task on hand as per Proposed welding procedure specification i.e. PWPS (essential, supplementary essential, and non-essential variables) and a piece of the plate will be used to set the current, voltage and travel speed which will be measured appropriately. An AC/DC Clamp meter (Figure 9) can be used for this purpose.

    Figure 9

    AC/DC Clamp meter

     

    Step 7:

    Now the Welder shall start welding, as per the proposed welding procedure (PWPS), and at least one welding engineer per test coupon shall be deputed to record the parameters on the parameter format (Click here for a sample of recommended parameter record sheet). For details on Shielded Metal Arc Welding (SMAW), please click here and to learn Gas Tungsten Arc welding process (GTAW / TIG welding), please click here.

    Step 8:

    In most of the cases, the root run after its completion is witnessed by the TPI and he/she signs the sheet and allows the rest of the welding but all the passes can be witnessed by the TPI (Refer 2nd page of the parameter sheet as mentioned in Serial No. 8). For Measuring Preheat and interpass temperature following items can be used.

    1. Infrared Pyrometer (Figure 10)
    2. Thermal Chalk (Figure 11)
    Figure 10

     

    Figure 11

    thermal chalk

     

    Step 9:

    All the parameters need to be recorded on the parameters sheet (as mentioned in Serial No 8) and after completion of the test coupon welding be signed by Welding Engineer and TPI.

    Step 10:

    Test Coupon (Single Side Welded – GTAW & GTAW + SMAW process) is allowed to cool below 30°C before removing the backing supports to avoid any spring back effect (angular distortion) and for the test coupon (Double Side welded-SMAW process) also follow the above procedure and remove the back supports do back chip(Gouging/grinding etc..), allow the coupon to cool below 50° C and perform LPT (For Procedure Refer Link) and after successfully clearing it and then by again keeping the test coupon vertical complete the joint recording all the parameters.

    Step 11:

    Now generally the Pressure equipment manufacture possesses RT Facility (For procedure refer to link) or UT facility (For Procedure refer to link) the test coupon on both the sides shall have uniform bead profile so as to not interfere (Refer ASME SEC VIII DIV I for limits of reinforcement) with the interpretation of the results.

    Step 12:

    If there is any repair in the test coupon same shall be marked suitably and if the whole length of the test coupon is full of defects (Lack of Fusion, Inclusions, etc..) same shall be discarded and the above procedure until step no 12 needs to be repeated and if the test coupon clears either UT/RT a report of the same shall be prepared by ASNT NDE Level II qualified personnel which later on will become part of the PQR documentation.

    Step 13:

    Now test specimen marking shall be carried out manually and if an automatic facility exists the test specimen dimensions can be feed to the machine (Considering allowance for cutting and machining).

    Step 14:

    The Test specimens to be removed in the sequence as shown below in figure 12 (For Tensile and Bend Test only);

    Figure 12

    Impact test specimen

     

    Step 15:

    After their removal machining shall be carried out to make Transverse Tensile (02 No’s) per test coupon, 04 Side bend Test for thickness > 10 mm and 02 Face and 02 Root Bend test for Thickness < 10mm and impact test removal location shall be as per UG-84 of ASME SEC VIII DIV I (A separate article will deal with the cases for the location of impact test), additionally a sample for macro and micro examination may also be removed.

    Step 16:

    The “Transverse Tensile Test” shall (2 No’s per PQR) be performed in the Universal Tensile machine (Duly calibrated).

    Acceptance Criteria: the minimum tensile strength of the weaker of the two base metals ie 415 Mpa (SA 516 Gr 60).

    A Tensile test machine is shown in Figure 13.

    Figure 13

    Universal tensile test machine

     

    Step 17:

    The Transverse side bend (04 No’s) or transverse face bend (2 No’s) & transverse root bend (02 No’s) per PQR to be performed considering the mandrill diameter selected in reference to the thickness of test coupon mentioned in the ASME SEX IX.

    Acceptance Criteria: The weld and HAZ (Heat affected zone) of the transverse (side, root & face) shall be completely within the bend portion of the specimen after testing. The guided bend test specimen shall have no open discontinuity in the weld or HAZ (Heat affected zone) exceeding 3 mm in any direction on the convex surface of the specimen after bending.

    The bend test is shown in figure 14, given below;

    Figure 14

    Bend test for PQR

     

    Step 18:

    Impact test to be performed at (-)20°C [below the minimum design metal temperature (0°C)] with average absorbed impact value of 27 J (Acceptance) for weld and base metal.

    A single value of the specimen out of three of 20 J is also acceptable.

    An impact test machine is shown in figure 15.

    Figure 15

    Impact te

     

    Step 19:

    Macro Examination @ 20X magnification as per ASME SEC IX (Won’t be discussed further).

    Step 20:

    Micro Examination as per ASM handbook Volume 9 (Won’t be discussed further).

    Step 21:

    Now after successful completion of all the testings mentioned from Sr No 14 thru 20 PQR format to be filled with the details (essential variables, parameters recorded and the testing results and the same shall be endorsed with Welding Engineer and TPI for documentation (Click here to download the sample PQR format)

    (Note: The purpose of this article is to give a general guideline to the readers and it shall not be considered as a substitute of code. For full terms and conditions please read ASME Section VIII DIV I 2017 & ASME SEC IX 2017 edition).

    This article is written and published by;

    MR. SANDEEP SINGH PARMAR

    (Ex. GE, ISGEC & ESSAR)

    Email: sandeepparmar99@yahoo.com

    IWE (IN/IWE/41700026); B Tech (Mechanical); AMIIW (Welding Technology)

    ISO 9001:2008 Internal Auditor; ISO 9001:2015 Lead Auditor ;

    NDE L-II (UT, LPT, MPI, RT); Lean Six Sigma Green Belt;

    MWeldl IEng; MIE C Eng(Ind) ; M.I.Inst.W ; LM IIM

  • Summary of ASME BPVC Section VIII Div 1 (Part 3)

    Summary of ASME BPVC Section VIII Div 1 (Part 3)

    In Part-2 of this article, the Subsection A was covered from UG-17 up to UG-35 Design and to read the Part-2 of this article please click here.

    This article will deal with the general requirements preceding from UG-36 onwards.

    Also note that the design calculation won’t be dealt within details and the readers are advised to refer the code for their specific type of vessel design.

    To read the Interpretations of ASME Codes, Please click here.

    Shape of opening: It can be cylindrical or conical in shells and be elliptical, circular or obround in heads.

    Note: when the opening is other than as mentioned above the part of the vessel shall be subjected to a proof hydrostatic test in order to ascertain the safety of the pressure vessel.

    Size of the opening:

    • For vessels 1520 mm inside diameter and less, one- half the vessel diameter, but not to exceed 510 mm;
    • For vessels over 1520 mm inside diameter, one-third the vessel diameter, but not to exceed 1020 mm.
    • For an opening in an end closure, which is larger than one-half the inside diameter of the shell, one of the following alternatives to reinforcement may also be used:

    Strength and design of finished opening: Will discuss the matter related to welding only;

    • Welded, brazed, and flued connections meeting the applicable rules and with a finished opening not larger than: 89 mm diameter —in vessel shells or heads with a required minimum thickness of 10 mm or less;
    • 60 mm diameter —in vessel shells or heads over a required minimum thickness of 10 mm;
    • Openings through Welded Joints. Additional provisions governing openings through welded joints are given in UW-14.

    As an opening (nozzle, manway etc.) is cut in pressure equipment’s the load normally carried out by the metal removed must be carried out by the wall adjacent to the opening this added load (of the material removed) increases the stress adjacent to the opening and hence excess thickness (in shell/ nozzle) needs to be provided in form of reinforcement to carry the additional load.

    Figure shows stress distribution in a plate with circular opening. From above figure it is clear that the stress at the edge of the circular hole is 2.5 times the design stress and hence the area (in circumference) require reinforcement to avoid failure. For detailed calculation refer code.

    UG- 38: FLUED OPENING IN SHELLS & FORMED HEADS

    The minimum depth of flange exceeding 150 mm in any inside dimension, when not stayed by an attached pipe or flue, shall equal 3tr or tr+ 75 mm, whichever is less, where tr is the required shell or head thickness.

    There is no minimum depth of flange requirement for flued out openings. For others openings refer code.

    UG-39: REINFORCEMENT REQUIRED FOR OPENINGS IN FLAT HEADS

    Single opening: When the opening does not exceed 0.5 times the Head dia, the total cross sectional area of reinforcement required in the plane under consideration shall be determined from below formulae:

    Where;

    • d= finished dia/dimensions
    • t= specified vessel wall thickness
    • tn= nozzle wall thickness
    • fr1= allowable stress in nozzle/allowable stress in vessel

    Multiple openings: With dia equal to or less than 0.5 times the head diameter, and no pair with an average dia greater than 0.25 times the head dia may be reinforced as a single opening using the above mentioned formulae.

    When spacing between any pair of openings is less than 2 times but equal to or greater than 1.25 times the average diameter of the pair, the required reinforcement for each opening in the pair, as determined by above, shall be summed together and then distributed such that half of the sum is located between the two openings.

    Spacing’s of less than 1.25 times the average diameter of adjacent openings shall be treated by rules of U-2(g).

    For other types refer code.

    UG-40: LIMITS OF REINFORCEMENT

    The limits of reinforcement, measured parallel to the vessel wall, shall be at a distance, on each side of the axis of the opening, equal to the greater of the following:

    1. D (Dia of finished opening).
    2. Ri (inside radius) + tv (vessel thk)+ tn (nozzle thk).

    The limits of reinforcement, measured normal to the vessel wall, shall conform to the contour of the surface at a distance from each surface equal to the smaller of the following:

    1. 2.5*tv (vessel thk).
    2. 2.5*tn (nozzle thk) + te(as per UG-40).
    • For other details refer code.

    UG-41: STRENGTH OF REINFORCEMENT

    • Refer code for details

    UG-42: REINFORCEMENT OF MULTIPLE OPENING

    • Refer code for details

    UG-43: METHODS OF ATTACHMENT OF PIPE AND NOZZLE NECKS TO VESSEL WALLS

    • They can be welded, brazed, studded, threaded, expanded

    UG-44: FLANGE AND PIPE FITTINGS

    • Various standards are ASME B 16.1, ASME B 16.5, ASME B 16.9, ASME B 16.11, ASME B 16.15, ASME B 16.20, ASME B 16.24, ASME B 16.42, and ASME B 16.47.
    • For other details refer code.

    UG-45: NOZZLE NECK THICKNESS

    • For access opening

     

    • For other nozzles

     

     

    Where;

    • tUG-45= minimum wall thickness of nozzle necks
    • ta= minimum neck thickness required for internal & external pressure
    • tb1= minimum neck thickness required for internal pressure (+ Corrosion allowance)
    • tb2= minimum neck thickness required for external pressure (+ Corrosion allowance)
    • tb3= thickness given in below table (+Corrosion allowance)

    Nozzle minimum thickness requirements:

    Sr No. Nominal Size Minimum Wall Thickness (mm)
    1. DN 6 1.51
    2. DN 8 1.96
    3. DN 10 2.02
    4. DN 15 2.42
    5. DN 20 2.51
    6. DN 25 2.96
    7. DN 32 3.12
    8. DN 40 3.22
    9. DN 50 3.42
    10. DN 65 4.52
    11. DN 80 4.80
    12. DN 90 5.02
    13. DN 100 5.27
    14. DN 125 5.73
    15. DN 150 6.22
    16. DN 200 7.16
    17. DN 250 8.11
    18. DN 300 8.34

     

    UG-46: INSPECTION OPENINGS

    • For further details, refer code.

    UG-47: BRACED AND STRAYED SURFACES

    • For Further details, refer code

    UG-48-49-50: STAY BOLTS, ITS LOCATION & ITS DIMENSIONS

    • Refer code for details

    UG-53: LIGAMENTS

    • Pitch of tube holes in every row equal use below formulae; 
    • Pitch of tube holes in one of the row is unequal use below formulae;

    Where;

    • d= dia of tube holes
    • n= no of pitch holes in length p1
    • p= longitudinal pitch of the tube holes
    • p1= unit length of ligament

    Refer code for other details.

    UG-54-55: SUPPORTS, LUGS FOR PLATFORMS, LADDERS AND OTHER ATTACHMENTS TO VESSEL WALLS

    • Refer code for details

    UG-75: GENERAL FABRICATION

    • The exact necessities of ULW-75 agreed in the appropriate parts of subsection B and C shall be met.

    UG-76: CUTTING PLATES & OTHER STOCKS

    • For cutting of plates & other stocks machining, shearing, grinding, oxygen or arc cutting can be used.
    • All Slag and discoloration formed on surface by above means to be removed before fabrication.
    • Inside edges shall be rounded/chamfered.

    UG-77: MATERIAL IDENTIFICATION

    • Original marking on parts, traceability of parts to the original marking shall be maintained by the vessel manufacturer by suitable means.
    • Transfer of marking shall be before cutting and may or may not be witnessed by the inspector.

    • For other details refer code.

    UG-78: REPAIR OF DEFECTS IN MATERIALS

    • Inspector concurrence shall be obtained beforehand.

    UG-79: FORMING PRESSURE PARTS 

    • Limits of cold working are given in UCS-79(d), UNF-79(a), UHA-44(a), and UHT-79 (a) for various materials.
    • In order to avoid flat spots along the completed joints in a cylindrical shell proper rolling or forming shall be performed before fabrication.
    • When parts of vessel are cold formed by vendors, the certification for the part shall mention weather or not the part was heat treated.
    • The following conditions shall be met for accepting reduction in part thickness due to forming:
    1. Inspector check the part compliance from UW-35(a) thru UW-35(d) prior to forming.
    2. Forming shall not reduce the part thickness below design requirements.
    3. Max Reduction =1mm or 10% of nominal thk of adjoining surface, whichever is less.

     

    Table UG-79-1

    Equations for Calculating Forming Strains
    Sr No Type of Part Being Formed Forming Strains
    1. Cylinders formed from plate Ƹf =(50*t/Rf)*(1-Rf/R0)
    2. For double curvature (eg, heads) Ƹf =(75*t/Rf)*( 1-Rf/R0)
    3. Tube and pipe bends Ƹf =100*r/R

     

    Where;

    • Ƹf = extreme fiber elongation
    • Rf= final mean radius
    • R0= original mean radius
    • R= nominal bending radius to centerline of pipe

    (Note: Purpose of this article is to give a general guideline to the readers and it shall not be considered as a substitute of code. For full terms and conditions please read ASME Section VIII DIV I, 2017 edition).

    This article is written and published by;

    MR. SANDEEP SINGH PARMAR

    (Ex. GE, ISGEC & ESSAR)

    Email: sandeepparmar99@yahoo.com

    IWE (IN/IWE/41700026); B Tech (Mechanical); AMIIW (Welding Technology)

    ISO 9001:2008 Internal Auditor; ISO 9001:2015 Lead Auditor ;

    NDE L-II (UT, LPT, MPI, RT); Lean Six Sigma Green Belt;

    MWeldl IEng; MIE C Eng(Ind) ; M.I.Inst.W ; LM IIM

  • What is a Valve (Part – 1)

    What is a Valve (Part – 1)

    Introduction:

    Valves are mechanical devices, specifically designed to direct, start, stop, mix, or regulate the flow, pressure and temperature of process fluid.

    The need of Valve came after piping or plumbing. Plumbing dates back thousands of years in the civilization of human across globe.

    Valves can be found just about anywhere today, in our homes, under the street, in commercial buildings and in thousands of places within industrial and infrastructure facilities.

    The valve industry is broad with segments varying from water distribution to nuclear power to upstream and downstream oil and gas. Each of these end-user industries use some basic types of valves; however, the details of construction and materials are often very different.

    Let us see a brief history of valves in timeline:

    A special valve in the form of a hinged prism stone were used in the construction of Great Pyramid of Giza for regulation of water into pyramid chambers around 2560 BC.

    The Romans used lead piping to distribute water to cities and towns throughout the Roman Empire. The use of lead piping and use of valves to control the flow of water in these pipelines was prevalent in the 1 BC and for the next several centuries.

    Flap valves and coin valves were the forebears of the present swing and lift check valves and were used in the water force pumps. Bronze and brass plug cocks were in common use as stop valves on water mains and supply pipes to public and domestic buildings during the Roman period. A large bronze cock valve was found on Capri among the ruins of the Palace of Tiberius, built around 25 AD.

    Romans used a primitive diaphragm valve, made of crude leather that was manually closed over a weir, to control flow and temperature of household bath water.

    In 1681, the first safety valve was invented by Denis Papin.

    In 1784, it was believed butterfly valve was used by James Watt in his Steam Engine design.

    In 1840, The first valve patent granted in the United States went to James Robinson for his gate valve, or “stop cock,” as it was called at the time.

    In 1846, The globe valve design is developed and patented by Walworth. The most important fluid control need of the period was controlling and regulating steam flow, and the globe valve was the best design for the job.

    In 1875, groove-packed plug cock introduced by Dewrance & Co. This made the valve easier to operate and more suitable for use with steam.

    In 1886, Joseph Hopkinson introduced the parallel slide valve, in which the sealing of the valve was affected by the line pressure on the disc, which is still being manufactured today.

    The lubricated taper plug valve was developed during World War I by Sven Nordstrom, a Swedish engineer, who was trying to overcome the excessive leakage and sticking of ordinary plug valves.

    The first Mercedes car built around 1901 introduced a butterfly valve in the fuel intake linked to the accelerator pedal. The first butterfly valves used metal-to-metal seats but, after World War II, improvements in modern synthetic rubbers for the sealing members extended the application of the butterfly valve into many industrial fields.

    In 1907, Frank P. Cotter developed a “simple self-sealing check valve, adapted to be connected in the pipe connections without requiring special fittings and which may be readily opened for inspection or repair.

    The Modern diaphragm valve was developed by a South African engineer named Saunders, who, working in the gold mines, was faced with excessive leakage of compressed air at the glands of the valves being used. In 1929 he developed a valve using a diaphragm both to isolate the valve operating mechanism and to act as the closing member, which proved a great success.

    Watts Regulator Co. introduced the first automatic temperature and pressure relief valve in the late 1930s. The new valve opened and closed automatically on both pressure and temperature.

    In 1945, the first ball valve was designed by Landis H. Perry. Initially developed for fuel systems on aircraft during World War II, the valve was further developed in the post-war years to produce the first industrial range of ball valves.

    In 1953, Fujikin developed its first patented product, the Needle Valve was developed after the World War II, there was demand for more precise control of gas flow.

    Howard Freeman establishes Jamesbury Corp. Patent for the first bi-directional soft seated valve is applied in 1956 and the first pneumatic actuator produced in 1957.

    In 1975, Neles metal-seated Neldisc butterfly valves are introduced to the process industries. The revolutionary U-shaped metal seat and elliptic disc form a unique triple-offset valve design, which is commonplace in many butterfly valve products today.

    Classification of Valves:

    The valves are broadly categorized into various types by the following;

    • Function
    • Design
    • Application
    • Method of control
    • Port Type
    • Actuation

    Valves categorized by function;

    • On-Off / Isolation Valve: Function of blocking the flow or allowing it to pass.
    • Non-Return Valve: Function of allowing flow to travel in one direction only.
    • Throttling / Regulation Valve: Function of allowing flow at any point between fully open to fully closed.

    Valves categorized by design:

    • Globe Valve
    • Gate Valve
    • Plug Valve
    • Ball Valve
    • Butterfly Valve
    • Diaphragm Valve
    • Pinch Valve
    • Piston Valve
    • Needle Valve
    • Check Valve
    • Relief & safety Valve
    • Special Valve

    Valves categorized by application:

    • General Service Valve
    • Special Service Valve
    • Severe Service Valve

    Valves categorized by Method of Control:

    • Linear Motion Valve
    • Rotary Valve

    Valves categorized by Port Size:

    • Full Port Valve
    • Reduced Port Valve

    Types of Actuators:

    • Manual
    • Automatic

    Click here to read the next part of this article.

    This article is written and published by

    Mr. Goutham Rathinam

    (BE-Mechanical & CSWIP 3.1-TWI,UK)             

    Email ID: goutham.r86@gmail.com

  • Summary of ASME BPVC Section VIII Div 1 (Part 2)

    Summary of ASME BPVC Section VIII Div 1 (Part 2)

    In Part-1 of this article we had discussed about what ASME SEC VIII DIV I deals, code cases, scope, its use and body of the code. The Subsection A was covered up to UG-16 (Design) and to read the Part-1 of this article please click here.

    This article i.e part – 2 will deal with the general requirements preceding from UG-17 onwards.

    Please note that the design calculations won’t be dealt in detail, and the readers are advised to refer the code for their specific type of vessel design.

    Subsection A (UG – 17 onwards)

    UG- 17: METHODS OF FABRICATION IN COMBINATION

    A Combination of fabrication methods can be used for design and fabrication of pressure equipment’s as per this code.

    UG- 18: MATERIALS IN COMBINATION

    Any combination of material as mentioned in Subsection C of this code can be utilized in construction of a vessel and joining of dissimilar joints requirements of ASME SEC IX shall be met.

    The rules of the code shall govern the necessities for the parent metal its heat affected zone (HAZ) and weld metal(s) in case the parent metals of different metallurgies needs to be joined together.

    Say, for example when SA 516 Gr 70 (Carbon Steel) is welded directly to SA 240 TP 316L (Austenitic Stainless Steel) using E Ni Cr Fe-3 (SMAW Process) as filler metal the applicable rules of this division shall apply to each of the following separately:

    • CS parent metal & HAZ
    • ASS parent metal & HAZ
    • Ni Filler Metal

    UG- 19: SPECIAL CONSTRUCTION

    Combination units: won’t discuss this further (types are mentioned below).

    • Common Element Design
    • Differential Pressure Design
    • Mean Metal Temperature Design
    1. Special Shapes
    2. When no design rules are given the max allowable working pressure of the completed vessel shall be established in accordance with provisions of UG-101.

    UG- 20: DESIGN TEMPERATURE

    Maximum temperature: For the parts under consideration maximum temperature shall be greater than the average metal temperature through thickness of the vessel expected in service except for lethal service. It can be derived by measurement from a similar equipment in service. (Refer WRC Bulletin 470, “Recommendations for Design of Vessels for Elevated Temperature Service” has information that may prove helpful to the vessel designer).

    Minimum temperature: It shall be the lowest expected temperature experienced by the pressure equipment in service and accordingly the plate, casting, forgings, fittings etc shall be selected for construction.

    Designer shall keep in mind the lowest operating temperature in service, the surrounding temperature, the effects of immediate startup and shut down etc. while designing the pressure equipment.

    Methods of obtaining the service temperature is also mentioned in the non-mandatory appendix of this code.

    As there is greater risk of brittle failure for carbon and low alloy steel so following requirements to be met for impact test exemptions:

    (1) For P-No. 1, Gr. No. 1(SA 516 Gr 60) or 2 (SA 516 Gr 70), can only be used if the requirements of (a) and (b) below are met:

    (a) Curve A material max thickness restricted to 13 mm

    (b) Curve B, C and D materials thickness restricted to 25 mm.

    (2) The complete pressure equipment to be either hydrostatically or pneumatically tested with the provisions of this code.

    (3) Designer shall ensure the temperature range is between 345°C and -29°C. However irregular temperature below -29°C may be allowed.

    UG-21: DESIGN PRESSURE

    Each part of pressure containing equipment must be designed for worst combination of equivalent pressure and temperature expected in normal operation.

    UG-22: LOADINGS

    The loadings for designing a pressure vessel shall include the following

    • Internal /external design pressure, test pressure and coincident static head, abnormal pressure.
    • Weight of the vessel and normal contents under operating or test conditions;
    • The internal (Tray Support Ring) and external attachments (Lugs, Skirts etc…)
    • Wind, snow, and seismic reactions, impact reactions; superimposed static reactions from weight of attached equipment (piping, lining etc.…), cyclic and dynamic reactions (due to pressure, thermal variations etc……)
    • Temperature gradients and differential thermal expansion

    UG-23: MAXIMUM ALLOWABLE STRESS VALUES

    The Designer shall utilize Section II, Part D, and Sub-part 1 for getting the values of maximum allowable tensile stress meant for different materials. For material identified as meeting more than one material specification and/or grade, the maximum allowable tensile stress value for either material specification and/or grade may be used provided all requirements and limitations for the material specification and grade are met for the maximum allowable tensile stress value chosen.

    S.N.

    		 Table No

    Title
    1. UCS-23 CS & LAS (Stress Values in Sec II Part D, Sub-part 1, Table 1A & Table 3 respectively.
    2. UNF 23.1 thru UNF 23.5 Nonferrous metals (Stress Values in Sec II Part D, Sub-part 1, Table 3 and Table 1B).
    3. UHA-23 HAS (Stress Values in Sec II Part D, Sub-part 1, Table 3 and Table 1A or 1B).
    4. UCI-23 Max Allowed Tensile Stress for CI.
    5. UCD-23 Max Allowed Tensile Stress for Cast Ductile Iron.

    S.N.

    		 Table No.

    Title
    6. UHT-23 Heat Treatment Enhanced Ferritic Steels (Sec II Part D, Subpart1, Table 1A).
    7. ULT-23 Max Allowed Tensile Stress for 5%, 8% and 9% Ni Steels and 5083-0 Al alloy below -196 Degree C temp for welded and non-welded construction.

     

    Designer in designing cylindrical shells or tubes using welded or non-welded product form shall choose the maximum allowable compressive stress values in longitudinal direction which are subjected to loadings that produce compression in longitudinal direction of the shell or tube be the least of the following:

    (1) Max.allowable tensile stress permitted as per code;

    (2) Value of B as determined below:

    E = modulus of elasticity of material at design temperature.

    R0 = outside radius of cylindrical shell or tube

    t = the minimum required thickness of the cylindrical shell or tube

    The joint efficiency for butt-welded joints shall be taken as unity.

    The value of B shall be determined as follows:

    Step 1: Using the value of R0 and t, calculate factor “A” from the below equation:

    Step 2: Enter material chart in Section II Part D Sub-part 3.

    Step 3: If A to the right of the scale (material/temperature line) than extend appropriate temperature line horizontally to right and read value of B.

    Step 4: If the value of A of left of the scale (material/temperature line) calculate B as follows:

    (For more ways to calculate the value of B refer ASME SEC VIII DIV I)

    UG-24: CASTINGS:

    Quality Factor: A factor not to exceed 80% shall be applied to static castings that are examined in accordance with the minimum requirements of the material specification, in addition all the surfaces of centrifugal castings shall be machined after heat treatment to a finish not coarser than 6.3 micro m, arithmetic average deviation, and a factor not exceeding 85% shall be applied.

    For nonferrous and ductile cast iron materials, the factor shall be taken from code.

    For carbon, low alloy, or high alloy steels, higher quality factors may be applied if in addition to the minimum requirements mentioned in the first point above.

    For other additional requirements (Vessels to be used in Lethal Service) refer code.

    Identification and Marking: Each casting to which a quality factor greater than 80% is applied shall be marked with the name, trademark, or other traceable identification of the manufacturer and the casting identification, including the casting quality factor and the material designation.

    UG-25: CORROSION

    Pressure equipment’s and its parts in which material thickness is reduced by rusting, wearing away, or by mechanical scratch shall be considered by designer so that the equipment perform as required for the period of time to which it was designed by the following two ways:

    Utilizing the data available for the corrosion rate thereby increasing the thickness over those for which pressure equipment was designed.

    Utilizing other methods such as painting, cathodic protection, hard facing, corrosion resistant overlays etc.…

    Rate of attack (Corrosion) may be different for different parts of the pressure equipment’s and accordingly the allowance shall be added.

    Indicative Hole: These holes can be used to provide the information that the original design thickness may have reduced to the alarming levels. They shall not be used in the pressure equipment’s meant for lethal service.

    Drain passage: Pressure equipment’s undergoing rusting should have drain passage at the lowest point practicable in the pressure equipment; or a pipe may be used extending inward from any other location to within 6 mm of the lowest point.

    UG-26: LININGS

    The wall thickness only shall be considered for strength calculation disregarding the rust resistant and wear resistant linings.

    UG-27: THICKNESS OF SHELL UNDER INTERNAL PRESSURE:

    Circumferential Stress (Longitudinal Joints): When the thickness does not exceed one-half of the inside radius, or P does not exceed 0.385SE, the following formulas shall apply:

    Longitudinal Stress (Circumferential Joints): When the thickness does not exceed one-half of the inside radius, or P does not exceed 1.25SE, the following formulas shall apply:

    Spherical Shells: When the thickness of the shell of a wholly spherical vessel does not exceed 0.356R,or P does not exceed 0.665SE, the following formulas shall apply:

    Where:

    • E = joint efficiency for, or the efficiency of, appropriate joint in cylindrical or spherical shells, or the efficiency of ligaments between openings, whichever is less. For welded vessels, use the efficiency specified in UW-12. For ligaments between openings, use the efficiency calculated by the rules given in UG-53.
    • P = internal design pressure (see UG-21)
    • R =inside radius of the shell course under consideration,
    • S = maximum allowable stress value (see UG-23 and the stress limitations specified in UG-24)
    • t = minimum required thickness of shell

    UG-28: THICKNESS OF SHELL UNDER EXTERNAL PRESSURE:

    For further details, refer code.

    UG-29: STIFFINING RINGS FOR CYLINDRICAL SHELLS UNDER EXTERNAL PRESSURE

    The available moment of inertia of a circumferential stiffening ring shall be not less than that determined by one of the following two formulas;

    Where:

    I = available moment of inertia of the stiffening ring cross section about its neutral axis parallel to the axis of the shell

    Is= required moment of inertia of the stiffening ring cross section about its neutral axis parallel to the axis of the shell

    I’ = available moment of inertia of combined ring-shell cross section about its neutral axis parallel to the axis of the shell.

    I’s= required moment of inertia of the combined ring- shell cross section about its neutral axis parallel to the axis of the shell.

    UG-30: ATTACHMENT OF STIFFINING RING

    Refer code for details

    UG-31: TUBES AND PIPES WHEN USED AS TUBES OR SHELLS

    Refer UG-27 and additionally the thickness as determined in UG-27 shall be increased when necessary to meet the following requirements:

    (1) Additional wall thickness should be provided when corrosion, erosion, or wear due to cleaning operations is expected.

    (2) Where ends are threaded, additional wall thickness is to be provided in the amount of (20/n mm) [Where n equals the number of threads per 25.4 mm]

    UG-32: FORMED HEADS, AND SECTIONS, PRESSURE ON CONCAVE SIDE

    Ellipsoidal Heads with ts/L ≥ 0.002: The required thickness of a dished head of semi ellipsoidal form, in which half the minor axis (inside depth of the head minus the skirt) equals one-fourth of the inside diameter of the head skirt, shall be determined by;

    Torispherical Heads with ts/L ≥ 0.002: The required thickness of a tori spherical head for the case in which the knuckle radius is 6% of the inside crown radius and the inside crown radius equals the outside diameter of the skirt shall be determined by;

    Hemispherical Heads: When the thickness of a hemispherical head does not exceed 0.356L, or P does not exceed 0.665SE, the following formulas shall apply;

    Conical Heads and Sections (Without Transition Knuckle): The required thickness of conical heads or conical shell sections that have a half apex-angle a not greater than 30 deg shall be determined by;

    Where,

    D = inside diameter of the head skirt; or inside length of the major axis of an ellipsoidal head; or inside diameter of a conical head at the point under consideration,

    Measured perpendicular to the longitudinal axis

    Di = inside diameter of the conical portion of a tori conical head at its point of tangency to the knuckle, measured perpendicular to the axis of the cone = D – 2r (1 – cos a)

    E = lowest efficiency of any joint in the head; for hemispherical heads this includes head-to-shell joint; for welded vessels, use the efficiency specified in UW-12

    L = inside spherical or crown radius. The value of L for ellipsoidal heads shall be obtained from Table UG-37.

    P = internal design pressure (see UG-21)

    r = inside knuckle radius

    S = maximum allowable stress value in tension as given in the tables referenced in UG-23, except as limited in UG-24 and (d) below.

    t = minimum required thickness of head after forming

    ts= minimum specified thickness of head after forming. (mm). ts shall be > = t

    a = one-half of the included (apex) angle of the cone at the centerline of the head

    UG-33: FORMED HEADS, AND SECTIONS, PRESSURE ON CONVEX SIDE

    Refer code for details.

    UG-34: UNSTAYED FLAT HEAD AND COVERS

    Refer code for details.

    UG-35: OTHER TYPES OF CLOSURES:

    The names will be mentioned only, these are

    • UG -35.1 Dished Covers
    • UG-35.2 Quick -Actuating closures
    • UG35.3 Quick-Opening closures

    Please click here to read the next part of this article.

    (Note: Purpose of this article is to give a general guideline to the readers and it shall not be considered as a substitute of code. For full terms and conditions please read ASME Section VIII DIV I, 2017 edition)

    This article is written and published by;

    MR. SANDEEP SINGH PARMAR

    (Ex. GE, ISGEC & ESSAR)

    Email: sandeepparmar99@yahoo.com

    IWE (IN/IWE/41700026); B Tech (Mechanical); AMIIW (Welding Technology)

    ISO 9001:2008 Internal Auditor; ISO 9001:2015 Lead Auditor ;

    NDE L-II (UT, LPT, MPI, RT); Lean Six Sigma Green Belt;

    MWeldl IEng; MIE C Eng(Ind) ; M.I.Inst.W ; LM IIM

  • How To Make Weld Map, Shop Weld Plan, WPS, PQR & WPQ for A Static Pressure Vessel (Part-1)

    How To Make Weld Map, Shop Weld Plan, WPS, PQR & WPQ for A Static Pressure Vessel (Part-1)

    Scope:

    This article will deal with step by step guide for the preparation of Weld Map, Shop Weld Plan, WPS, PQR & WPQ as per ASME SEC IX for a Static Pressure Vessel designed in accordance with ASME SEC VIII DIV I for non-lethal Service.

    The Reader must be wondering from where this requirement of Weld Map and Weld Plan arises which is very common thinking when one (Welding Engineer) is making them for the first time as many a time it is mandatory as per customer/client specification and also if a company is ISO 9001 certified along with U  stamp designator holder as per ASME SEC VIII DIV I so to enable inspector and customer of knowing what was approved, what was followed and as-built information communication both Weld Map and Shop Weld Plan are required.

    Weld Map: A document which includes but not limited to a Sketch of the equipment locating all the welds along with a table with all the details (Material, thickness, welding process, WPS, PQR etc…) required for getting customer/client/TPI approval.

    Definitions:

    Shop Weld Plan: A document prepared based on weld map & drawings approved by the customer which mentions specific seam no with WPS parameters, WPQ, etc., which is issued to shop for the fabrication activities.

    WPS: It stands for welding procedure specification which is a document directing welding personnel (supervisors, welders, operators) for details like the Type of Joints, Base metals, Filler metals, Position, Preheat, PWHT, Gas(es), Electrical characteristics and Technique to be used for joining of metals. The WPS will include all the variables like Essential, Supplementary Essential, and Non-Essential Variables (To learn more about WPS, Please click here).

    PQR: It stands for procedure qualification record and it documents all the essential variables and additional details recorded during its qualification, the testings (Nondestructive and destructive) carried out and signed by Welding Engineer and in most of the cases reviewed/witnessed by TPI (Third party inspector) depending on the customer/client requirements. The Non-Destructive Testing (NDT) may include: Visual, LPT, MPI, RT, UT, etc. and the destructive tests (DT) may include: Fracture (Room temp Tensile, Bend, Impact), Fatigue (CTOD, etc..), Corrosion (HIC, SSC, IGC, etc.…), Creep (Hot Tensile, S-N Diagram), Embrittlement (Temper Embrittlement – Step Cooling etc…).

    We shall now discuss the step by step procedure for the creation and approval of the Weld Map;

    The sketch of a Static Pressure Vessel, designed as per ASME SEC VIII DIV-I is as below;

    Note: Every effort was being made so that our pressure vessel (PV) design seems compliant to ASME SEC VIII DIV I, however, the author accepts no responsibility whatsoever in this regard.

    Bill of Materials is as mentioned below:

    Note: The author has not considered the base ring below the skirt and the RF Pad for manway, earthing lug of ASS, Lifting Lug, and any other internal or external attachment for making it easier for the reader to understand.

    From above, the author will utilize GTAW & SMAW process (as per ASME SEC IX) for procedure and performance qualification and considering the minimum design metal temperature (MDMT) of the Vessel to be 0 °C there are no impact requirements applicable (Refer UCS -66) and also the governing thickness (Refer UW-40 for details) is less than 38 mm there is no need to carry out post-weld heat treatment (PWHT).

    The material combination utilized, will be SA 516 Gr 70 and SA 516 Gr 60 as a smart welding engineer will be able to utilize it for welding of P1 G2 and P1 G1 (Note: P1, G1 & G2 are parent metal grouping, to learn more about metal grouping, please click here) when there is impact test requirement.

    After having the above information, proposed Weld Map and WPS are made, considering this is the first Job to be executed by Company Name: Welding and NDT  for approval of customer/client/TPI a sample of both are attached below:

    Proposed WPS No: GS-001 (Click here to download the proposed WPS)

    Proposed WPS No: S-001 (Click here to download the proposed WPS)

    Proposed WPS No: G-001 (Click here to download the proposed WPS)

    Considering the above situation the Welding Engineer needs to plan the welder qualification (WPQ) too, as the above WPS after qualification will be utilized for Welder qualification.

    Proposed Welder List for Qualification

    Shop Weld plan will be prepared once WPS and WPQ gets qualified and may or may not require customer/Client approval but may require inspector approval.

    Please click here to read the next part of this article.

    (Note: The purpose of this article is to give a general guideline to the readers and it shall not be considered as a substitute of code. For full terms and conditions please read ASME Section VIII DIV I 2019 & ASME SEC IX  2019 edition).

    This article is written and published by;

    MR. SANDEEP SINGH PARMAR

    (Ex. GE, ISGEC & ESSAR)

    Email: sandeepparmar99@yahoo.com

    IWE (IN/IWE/41700026); B Tech (Mechanical); AMIIW (Welding Technology)

    ISO 9001:2008 Internal Auditor; ISO 9001:2015 Lead Auditor ;

    NDE L-II (UT, LPT, MPI, RT); Lean Six Sigma Green Belt;

    MWeldl IEng; MIE C Eng(Ind) ; M.I.Inst.W ; LM IIM

  • Summary of ASME BPVC Section VIII Div 1 (Part 1)

    Summary of ASME BPVC Section VIII Div 1 (Part 1)

    ASME SEC VIII DIV I deals with the rules for the construction of pressure vessels. This code is a part of ASME BPVC Codes (Click here to learn about the various codes published by ASME).

    Code Cases are published regularly by the BPVC committee to consider proposed additions and revisions to the code and to formulate cases to clarify the intent of existing requirements when the need is urgent.

    These code cases will be incorporated into the preceding editions (Say for example those code cases which are adopted after 2017 edition up to 2019 will be reflected in 2019 edition).

    Scope of ASME Section VIII Div. 1

    This Code contains compulsory requirements, specific prohibitions, and non-mandatory guidance for pressure vessel materials, design, fabrication, examination, inspection, testing, and certification, and pressure relief.

    This code is not a handbook and cannot replace education, experience, and use of engineering judgment. The use of engineering judgment should not be used to overrule the mandatory requirements of this code.

    Use of Code:

    The Code is published every two years now and becomes mandatory after six months of its publication (For example ASME SEC VIII DIV I published on July 1 2017 becomes mandatory from Jan 1, 2018).

    The Body of ASME SEC VIII DIV I:

    Subsection A: General Requirements

    • Part UG: General Requirements for All Methods of Construction and All Materials

    Subsection B: Requirements pertaining to the Methods of Fabrication of Pressure Vessels

    • Part UW: Requirements for Pressure Vessels Fabricated by Welding
    • Part UF: Requirements for Pressure Vessels Fabricated by Forging
    • Part UB: Requirements for Pressure Vessels Fabricated by Brazing

    Subsection C: Requirements Pertaining to the Classes of Materials

    • Part UCS: Requirements of Pressure Vessels Constructed of Carbon and Low alloy Steel
    • Part UNF: Requirements of Pressure Vessels Constructed of Non Ferrous Materials
    • Part UHA: Requirements of Pressure Vessels Constructed of High Alloy Steel
    • Part UCI : Requirements of Pressure Vessels Constructed of Cast Iron
    • Part UCL: Requirements for Welded Pressure Vessels Constructed of Material with Corrosion Resistance Integral Cladding, Weld Metal Overlay Cladding, or Applied Linings
    • Part UCD: Requirements of Pressure Vessels of Cast Ductile Iron
    • Part UHT: Requirements of Pressure Vessels of Ferritic Steels with Tensile Properties Enhanced by Heat Treatment
    • Part ULW: Requirements of Pressure Vessels Fabricated by Layered Construction
    • Part ULT: Alternate rules for Pressure Vessels Constructed of Materials having Higher Allowable Stresses at Low Temperature.
    • Part UHX: Rules for Shell and Tube Heat Exchangers
    • Part UIG: Requirements of Pressure Vessels Constructed of Impregnated Graphite
    • Part UCD: Requirements of Pressure Vessels of Cast Ductile Iron

    Mandatory Appendix

    Non Mandatory Appendix

    Figures, Tables & Forms

    Figure 1: A snapshot of ready to Dispatch Pressure Vessel

    Figure 2: A snapshot of ready to Dispatch Pressure Vessel (Shell and Tube Type Heat Exchangers)

    Note: In this part of the article we will cover Subsection A (with focus on welding)

    Subsection A

    UG 1: SCOPE

    The requirements in this section apply to all pressure vessels and vessel parts and shall be used jointly with the specific requirements as given in Sub Section B, C, and Mandatory Appendices.

    UG 4: MATERIALS

    Materials for Pressure Parts Shall conform to the requirements given in ASME SEC II Part D, subpart 1. Table 1A, 1B, and 3 including all the applicable notes. Materials can be Dual Certified (For Example a plate can be certified as SA 516 Gr 60 and SA 516 Gr 70 as per ASME SEC II PART A by mill provided the material meets all the requirements of the identified material specification or grades.

    Non Pressure parts (Lugs, Skirts, etc…) need not be identified but in a case attached by welding shall be of weldable quality.

    Materials other than those allowed by the rules of this division shall not be used.

    Engineering judgment to be used by the manufacturer to assure the user that the materials used for the construction of pressure vessels will perform satisfactorily for the intended service. Refer informative guidance regarding the metallurgical phenomenon in ASME SEC II part D non mandatory appendix A.

    The material physical properties required by design shall be taken from ASME SEC II Part D subpart 2. If the Code does not contain the properties values the manufacturer may use other authoritative sources for the needed information. The manufacturer MDR in the remarks shall mention the source of the information.

    UG-5-6-7-8: BASE MATERIALS

    The Plate, Forgings, Castings, Pipe, and Tubes used in the construction of pressure vessels for pressure parts shall conform to the requirements of specific clauses except as otherwise permitted.

    UG-9: WELDING MATERIALS

    The welding material must comply with the requirements of this code, ASME SEC IX, Qualified WPS, and ASME SEC II Part C

    UG-10: MATERIALS IDENTIFIED WITH OR PRODUCED TO A SPECIFICATION NOT PERMITTED BY THIS DIVISION, AND MATERIAL NOT FULLY IDENTIFIED

    • Any unspecified material (single production lot) for the construction of vessel may be accepted provided the following conditions are met:
    1. Recertification shall be vessel and part manufacturer only.
    2. The documentation shall be available to show to the part or vessel manufacturer that all the requirements of this code are met. Material marking acceptable to the inspector.
    • If any material with the specification which is not permitted by ASME Section VIII Div. 1 but belongs to a particular production lot as per the requirements of a specification permitted by this division, but which cannot be qualified in above condition shall meet the following conditions to be acceptable:
    1. Recertification shall be by the vessel and part manufacturer only.
    2. When documentation demonstrating complete conformance to the chemical requirements is not available, chemical analyses are made on different pieces from the lot to establish a meaningful analysis that is to be accepted as representative of the lot. The chemical analysis shall conform to the specifications.
    3. Those mechanical properties which are not reported shall be tested and should conform to the specification.
    4. The material if not heat treated as per specification shall be heat treated either before or during fabrication.
    5. All other applicable requirements (including, but not limited to, melting method, melting practice, deoxidation, chemical analysis, mechanical properties, grain size, and quality) of the specification permitted by this Division, to which the material is to be recertified, have been demonstrated to have been met.
    6. The material marking shall be acceptable to the inspector and the material shall be marked as required by the specifications.
    • Material not fully identified: Won’t discuss this part in detail as it would be recommended to avoid such material in pressure vessels.

    UG-11: PRESSURE PARTS (PREFABRICATED OR PREFORMED) FURNISHED WITHOUT A CERTIFICATION MARK

    • The pressure parts (Prefabricated or preformed) to be used for pressure vessels, which are subject to stresses due to pressure and have been furnished by others or by the manufacturer (of the completed vessel) shall conform to all applicable requirements of this Division.
    • Parts that are prefabricated (Preformed) may be supplied as follows :
    1. Cast, forged, rolled, or die formed non-standard pressure parts: Pressure parts like shells, heads, etc. that are entirely formed by casting (ex: Shell), forging (ex: Nozzle, Shell), rolling (ex: Rolled Shell), or die forming (ex: Head) that do not require shop inspection may be supplied basically as materials.
    2. Cast (ex: Shell), forged (ex: Nozzle), rolled, or die formed (ex: Head) standard pressure parts that comply with an ASME product standard (ASME SEC II PART-A-B), either welded or seamless.
    3. Cast, Forged, Rolled, or Die Formed Standard Pressure Parts that comply with a standard other than an ASME product standard (ANSI Standard), either welded or seamless.
    4. The Code recognizes that manufacture (ASME Certificate Holder) may fabricate parts in accordance with UG-11(d), and that is marked in accordance with UG-11(d)(8).

    Instead of the requirement in UG-11(d)(4)(-a), the manufacturer may subcontract to an individual or organization not holding an ASME Certificate standard pressure parts that are fabricated to a standard other than an ASME product standard.

    UG-12-13-14: BOLTS & STUDS, WASHER & NUTS, RODS & BARS

    • UG-23, UCS-11 & UNF-13, Subsection-C to be followed for acceptance respectively

    UG-15 PRODUCT SPECIFICATION

    • For a  wrought (Forged, Rolled, Extruded, etc.…) product when there is no particular specification listed in subsection C, but there is an approved specification listed in subsection C of some other wrought product  of that grade  the product for which there is no specification can be provided
    1. The chemical and physical properties, heat treating requirements, and requirements for deoxidation, or grain size requirements conform to the approved specification listed in Subsection C.
    2. The manufacturing procedures, tolerances, tests, and markings are in accordance with a Section II specification covering the same product form (Forged, Rolled, Extruded etc…) of similar material.
    3. For the case of welded tubing made of plate, sheet, or strip, without the addition of filler metal, the appropriate stress values are reduced by 15%.
    4. The product is not pipe or tubing fabricated by fusion welding with the addition of filler metal unless it is fabricated following the rules of this Division as a pressure part.
    5. Mill test reports reference the specifications used in producing the material and also refer to this paragraph.
    • Example Alloy 316L is available as a plate and is listed under SA 240. It can be used as bar or pipe materials under SA-479 and SA-312, even though it is not listed under these specifications. The material must meet the chemical and physical requirements of SA 240 and the product and quality requirements of the applicable product specification).

    UG-16 DESIGN

    • The design of pressure equipment and its parts shall conform to the requirements in the following paragraphs and in addition to the specific requirements given in the applicable Parts of Subsections B and C.
    • Minimum thickness of pressure retaining components shall be 1.5 mm excluding corrosion allowance except that the above does not apply to heat transfer plates, inner pipe of double pipe heat exchangers for NPS 6(150), or less.
    • The minimum thickness of shells and heads of unfired steam boilers shall be 6 mm exclusive of any corrosion allowance.
    • The minimum thickness of shells and heads used in compressed air service, steam service, and water service, shall be 2.5 mm exclusive of any corrosion allowance.
    • This minimum thickness does not apply to the tubes in air-cooled and cooling tower heat exchangers if all the following provisions are met:
    1. The tubes shall not be used for lethal UW-2(a) service applications.
    2. The tubes shall be protected by fins or other mechanical means.
    3. The tube outside diameter shall be a minimum of 10 mm and a maximum of 38 mm.
    4. The minimum thickness used shall not be less than that calculated by the formulas given in UG-27 or 1-1 and no case less than 0.5 mm.

    The Plate Under Tolerance:

    1. Plate material shall not be ordered with a nominal thickness thinner than the design thickness.
    2. Plate material with an actual thickness less than the design thickness shall not be used unless the difference in thicknesses is less than the smaller of 0.3 mm or 6% of the design thickness.
    3. If plate material is ordered to a specification that allows an under tolerance greater than the smaller of 0.3 mm or 6% of the nominal thickness, the thickness of the plate ordered shall be increased, if required, so that the plate material will meet the requirement of (1.5 mm) when used.

    The Pipe Under Tolerance:

    1. Pipe and tube material may be ordered by its nominal wall thickness. However, manufacturing under tolerance must be taken into account when designing or ordering the component.
    2. The under tolerance need not be considered when designing nozzle wall reinforcement.
    • Corrosion Allowance Used in Design Formulas: It is included in every dimensional formula used in this code.
    • Examples showing the application of the design rules of this Division are contained in ASME PTB-4, ASME Section VIII, Division 1, and Example Problem Manual.

    Please click here to read the next part of this article.

    (Note: The purpose of this article is to give a general guideline to the readers and it shall not be considered as a substitute of code. For full terms and conditions please read ASME Section VIII DIV I).

    This article is written and published by;

    MR. SANDEEP SINGH PARMAR

    (Ex. GE, ISGEC & ESSAR)

    Email: sandeepparmar99@yahoo.com

    IWE (IN/IWE/41700026); B Tech (Mechanical); AMIIW (Welding Technology)

    ISO 9001:2008 Internal Auditor; ISO 9001:2015 Lead Auditor ;

    NDE L-II (UT, LPT, MPI, RT); Lean Six Sigma Green Belt;

    MWeldl IEng; MIE C Eng(Ind) ; M.I.Inst.W ; LM IIM

  • How to calculate heat input

    How to calculate heat input

    Heat input is a critical parameter for arc welding processes and it must be controlled to ensure sound weld quality.

    Heat input may be defined as “The amount of electrical energy that is supplied to a weld during the welding process”.

    How to calculate Heat input?

    There are several ways of calculating the heat input. We shall discuss the two most common methods of calculating the heat input.

    1. The American system (given in ASME BPVC Section IX – QW 409.1 (a) and various AWS standards):

    Heat input:

    Where,

    • Heat input is expressed in J/In (Joule/Inch) or J/mm (Joule/mm)
    • Voltage is expressed in Volts
    • Travel speed is expressed in In/min or mm/min

    The unit for heat input obtained by this formula shall be either in J/In or J/mm. To get the results in KJ/in or KJ/mm, divide the result by 1000.

    Example 1: If a welder takes 2 minutes to complete an 18 inches long weld. He keeps the voltage at 24 volts and the current 120 amps. What is your heat input?

    Answer:

    Given data parameters are;

    Travel Speed = Length of Weld/Time to weld = 18 inches/2 minutes = 9 in/min

    Voltage = 24 volts

    Current = 120 amps

    Heat Input = (24 X 120 X 60)/ 9 = 19200 J/in

    = 19.2 KJ/in (Divided by 1000 to obtain the result in KJ/in.)

    2. European system (given in EN ISO 1011-1 and PD ISO/TR 18491)

    An additional parameter of Thermal efficiency (process efficiency or arc efficiency) is used while calculating heat input as per European standards.

    Heat input:

    Value of thermal efficiency is different for different arc welding processes, see table 1:

    Table – 1

    Why Heat input is so important?

    Heat input affects the cooling rates in welds and thereby it affects the microstructure of the weld metal and that of the heat-affected zone (HAZ). A change in microstructure directly affects the mechanical properties of weld metal and heat-affected zone (HAZ). Therefore, it’s very important to control the heat input to achieve a sound microstructure and a good quality weld.

    Note: The heat input (as calculated by ASME standards) is referred to as “arc energy” under the European system. Hence the following formula holds true with regard to the European system;

    Heat input = Thermal efficiency X Arc energy