Interview Questions on Welding for Welding, QC Engineer and Third Party Inspector Jobs

Interview Questions on Welding for Welding, QC Engineer and Third Party Inspector Jobs

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Q1. What is the primary purpose of a welding procedure specification (WPS)? www.weldingandndt.com
  1. To outline the qualifications of the welder
  2. To specify the welding process and variables
  3. To determine the cost of the welding project
  4. To schedule welding activities

(Explanation: A Welding Procedure Specification (WPS) is a document that provides the details of the variables (parameters) such as joint design, base metal details, filler metal/electrode details, preheat, post heat, PWHT details, current, voltage, heat input details etc. to the welders or welding operators to create welds as per the requirements. The variables in the WPS are categorized as Essential Variables, Non-Essential Variables & Supplementary Essential Variables)

Q2. What is the difference between essential and non-essential variables in welding? www.weldingandndt.com
  1. Essential variables are considered to affect the mechanical properties of the weld (other than toughness properties), while non-essential variables do not.
  2. Essential variables are mandatory, while non-essential variables are optional.
  3. Essential variables are easily adjustable, while non-essential variables are fixed.
  4. Essential variables are related to safety, while non-essential variables focus on aesthetics.

(Explanation: Essential variables in welding is considered to affect the mechanical properties (other than toughness properties) of the joint. Therefore, any changes in the essential variables necessitate the re-qualification of the Welding Procedure Specification (WPS). This ensures that the welding process maintains its integrity and meets the required standards for strength, ductility, and other mechanical characteristics of the welded joint.)

Q3. What distinguishes an essential variable from a supplementary essential variable in a Welding Procedure Specification (WPS)? www.weldingandndt.com
  1. Essential variables impact the mechanical properties of the joint, while supplementary essential variables affect toughness properties.
  2. Essential variables are optional, whereas supplementary essential variables are mandatory.
  3. Essential variables focus on aesthetics, while supplementary essential variables ensure safety.
  4. Essential variables require re-qualification of the WPS, while supplementary essential variables do not.

(Explanation: Essential variables are considered to affect the mechanical properties of the weld and necessitate re-qualification of the WPS, if changed. On the other hand, supplementary essential variables primarily affect the toughness properties of the joint. Hence, If a supplementary essential variable is changed, it will affect the toughness properties of the joint, heat-affected zone, or base material (toughness property is also a mechanical property). Hence, Supplementary essential variables become additional essential variables when referencing code, standard, or specification requires toughness testing for procedure qualification. Hence, the WPS must be re-qualified. In other words we can say that the supplementary variables become just as important as essential variables when rules or standards require toughness testing for the welding process to be approved.)

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Q4. What does the term “preheating” refer to in welding?
  1. Heating the base metal before welding (www.weldingandndt.com)
  2. Cooling the welded joint after completion
  3. Applying heat to the filler material
  4. Inspecting the weld visually

(Explanation: Preheating in welding refers to the process of heating the base metal before starting the welding. This is done to raise the temperature of the base metal to a level that primarily retards or slows down the cooling rate of the molten weld pool. Preheating can also help to reduce the risk of thermal stresses and distortion during the welding process.)

Q5. Which of the below mentioned non-destructive testing method can be used to detect surface-breaking defects in welds which are not visible to the naked eye?
  1. Iron sulphide testing
  2. Ultrasonic testing
  3. Magnetic particle testing (www.weldingandndt.com)
  4. Visual inspection

(Explanation: Magnetic particle testing (MT) is a non-destructive testing method used to detect surface as well as sub-surface defects in welds. It involves applying a magnetic field to the weld, which causes any defects to become visible as magnetic particles adhere to the defects.)

Q6. What is the purpose of post-weld heat treatment (PWHT)? www.weldingandndt.com
  1. To cool down the welded joint gradually
  2. To relieve residual stresses and improve toughness
  3. To accelerate the cooling process of the weld
  4. To prevent oxidation of the weld metal

(Explanation: Post-weld heat treatment (PWHT) is a process used to improve the mechanical properties of a welded joint. It involves heating the welded joint to a specific temperature and holding it at that temperature for a certain period. PWHT helps to relieve residual stresses that can cause cracking and other defects in the weld. It also improves the toughness of the weld, making it more resistant to impact and fatigue.)

Q7. Which welding process uses a consumable electrode that also acts as a filler material? www.weldingandndt.com
  1. Gas Metal Arc Welding (GMAW)
  2. Shielded Metal Arc Welding (SMAW)
  3. Flux-Cored Arc Welding (FCAW)
  4. Gas Tungsten Arc Welding (GTAW)
  5. 1, 2 & 3

(Explanation: In all three cases i.e. GMAW, SMAW, & FCAW, the electrodes used in Gas Metal Arc Welding (GMAW), Flux-Cored Arc Welding (FCAW), and Shielded Metal Arc Welding (SMAW) are designed to act as filler materials. The main difference lies in the type of electrode and shielding gas used in each process:

  • GMAW uses a continuous wire electrode that also acts as a filler wire.
  • FCAW uses a tubular wire filled with flux at the core.
  • SMAW uses a coated electrode that melts and forms a molten pool, which is then solidified to create a strong joint.

In summary, all three welding processes use electrodes that act as filler materials, but they differ in the type of electrode and shielding gas used..)

Q8. What is the difference between PWHT and post heat in welding?
  1. The need for temperature monitoring
  2. The timing of the heat application
  3. The type of joint configuration
  4. The impact on visual appearance

(Explanation: Post-Weld Heat Treatment (PWHT) involves heat treatment applied after welding to relieve residual stresses and enhance mechanical properties. On the other hand, post-heat refers to heat applied immediately after a specific welding pass to control cooling rates and prevent cracking. Understanding the timing of heat application distinguishes these two practices in welding.)

Q9. What is the significance of interpass temperature control in multi-pass welding? www.weldingandndt.com
  1. It ensures uniform heat distribution throughout the weld
  2. It prevents excessive heat input and distortion
  3. It minimizes the risk of hydrogen-induced cracking
  4. It improves the fusion between weld passes

(Explanation: Controlling interpass temperature prevents hydrogen from accumulating in the weld, reducing the likelihood of cracks. By maintaining specific temperature ranges between subsequent weld passes, the cooling rate is controlled, reducing the potential for hydrogen absorption and cracking in the weld metal.)

Q10. What is the purpose of using a back gouging process in welding?
  1. To remove surface contaminants before welding
  2. To create a beveled edge for welding preparation
  3. To inspect internal defects in welded joints
  4. To enhance post-weld heat treatment effectiveness

(Explanation: The back gouging process in welding involves removing material from the root side of a weld joint to create a beveled or grooved edge. This preparation is done to facilitate proper welding penetration and fusion when joining the two pieces of metal. It allows for better access to the joint and ensures the welding from root side could be done in a proper way.)

Q11. What is the purpose of visual inspection of weld joints?
  1. To measure the hardness of the weld
  2. To assess the weld’s mechanical properties
  3. To visually check for surface defects and discontinuities
  4. To determine the chemical composition of the weld

(Explanation: Visual inspection of weld joints involves visually examining the welded joint to identify surface defects and discontinuities such as cracks, porosity, undercut, incomplete penetration (if joint is accessible from the root side), and other visible irregularities. While it provides valuable information about the overall quality and appearance of the weld, it does not measure hardness, assess mechanical properties, or determine the chemical composition of the weld.)

Q12. What is the purpose of a Charpy V-notch test?
  1. To measure the hardness of the weld
  2. To assess the impact toughness of the weld (www.weldingandndt.com)
  3. To determine the tensile strength of the weld
  4. To evaluate the ductility of the weld

(Explanation: The Charpy V-notch test evaluates how well a weld can absorb energy under impact, indicating its resistance to sudden loads or shocks. This test helps assess the weld’s ability to withstand sudden stress without fracturing, providing crucial insights into its toughness and reliability.)

Q13. What is the purpose of a Dye Penetrant Test in welding inspection?
  1. To measure the hardness of the weld
  2. To detect surface-breaking defects in the weld
  3. To assess the impact toughness of the weld
  4. To determine the chemical composition of the weld

(Explanation: A Dye Penetrant Test is used to identify surface defects like cracks, porosity, or laps that are not visible to the naked eye by applying a colored dye that penetrates these imperfections, making them visible for inspection.)

Q14. What does the term “Welding Position” refer to in welding procedures?
  1. The orientation of the welder during welding
  2. The location where welding is performed
  3. Orientation and configuration of the joint being welded
  4. The angle at which the electrode is held during welding

(Explanation: Welding Position describes the specific orientation and configuration of the joint being welded, such as flat, horizontal, vertical, or overhead, which influences welding technique and parameters.)

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Q15. What is the primary function of a Radiography Test (RT) in welding inspection?
  1. To measure the thickness of the weld
  2. To assess the hardness of the weld
  3. To detect internal defects in the weld
  4. To determine the tensile strength of the weld

(Explanation: Radiography Testing involves using X-rays or gamma rays to examine internal weld structures for defects like cracks, voids, or lack of fusion etc. that may not be visible externally.)

Q16. What is the primary purpose that distinguishes Post-Weld Heat Treatment (PWHT) from post-heat in welding?
  1. Improving visual appearance
  2. Controlling cooling rates during welding
  3. Relieving residual stresses and enhancing mechanical properties
  4. Minimizing the risk of thermal distortion

(Explanation: While both PWHT and post-heat involve the application of heat in welding, PWHT is specifically designed to relieve residual stresses and improve mechanical properties, setting it apart from post-heat, which focuses on controlling cooling rates during the welding process.)

Q17. What is the purpose of conducting a Positive Material Identification (PMI) test on incoming materials?
  1. To measure the hardness of the material
  2. To verify the chemical composition of the material
  3. To assess the tensile strength of the material
  4. To evaluate the impact toughness of the material

(Explanation: Positive Material Identification (PMI) inspection is primarily used to analyze and identify the material grade and alloy composition. The fundamental principle of PMI involves utilizing analytical techniques like X-ray fluorescence (XRF) or optical emission spectroscopy (OES) to determine the elemental composition of materials without causing damage or alteration. This process is crucial for verifying the chemical composition of metals and alloys quickly and non-destructively, ensuring quality and safety control in various industries.)

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Q18. Why is it important to conduct a Visual Inspection on raw materials before welding?
  1. To determine the mechanical properties of the materials
  2. To identify surface defects or contaminants
  3. To measure the thickness of the materials
  4. To assess the hardness of the materials

(Explanation: Visual inspections help detect any visible defects, such as cracks, rust, or foreign materials, that could compromise weld quality if not addressed before welding.)

Q19. What does a Material Test Certificate (MTC) provide information about?
  1. Welding procedures used during fabrication
  2. Chemical composition and mechanical properties of materials
  3. Welder qualifications for specific projects
  4. Non-Destructive Testing (NDT) results on welded joints

(Explanation: MTCs provide essential information about raw materials, including their chemical composition, mechanical properties, and compliance with industry standards.)

Q20. What is the primary purpose of conducting Ultrasonic Testing (UT) on incoming materials?
  1. To measure the thickness of the materials
  2. To detect internal defects in the materials
  3. To assess the hardness of the materials
  4. To determine the chemical composition of the materials

(Explanation: UT is used to identify internal flaws like cracks or voids within material)

Q21. What is the primary objective of conducting a Bend Test on incoming raw materials?
  1. Assessing material hardness and wear resistance
  2. Evaluating material corrosion resistance capabilities
  3. Determining material ductility
  4. Identifying internal defects like cracks in raw materials

(Explanation: Bend Tests help assess how well a material can deform without breaking, indicating its ductility)

Q22. What is the primary purpose of Raw Materials Inspection in Quality Control?
  1. To check the color of materials
  2. To ensure materials meet specified quality standards
  3. To count the quantity of materials
  4. To verify the weight of materials

(Explanation: Raw Materials Inspection aims to assess whether incoming materials conform to predetermined quality criteria, ensuring that they meet the required standards for production.)

Q23. What does MTC stand for in the context of quality control?
  1. Material Testing Certificate
  2. Manufacturing Technical Checklist
  3. Material Traceability Code
  4. Material Tolerance Criteria

(Explanation: MTC, or Material Testing Certificate, is a crucial document providing information on the testing and compliance of materials with applicable standards.)

Q24. Which of the following is NOT a common incoming material inspection parameter?
  1. Dimensional accuracy
  2. Chemical composition
  3. Material hardness
  4. Employee attendance records

(Explanation: Incoming material inspection typically focuses on physical and chemical properties rather than personnel-related aspects.)

Q25. What is the significance of Material Traceability in Quality Control?
  1. It ensures materials are visible in the warehouse
  2. It helps track materials throughout the production process
  3. It verifies the weight of materials
  4. It counts the number of incoming materials

(Explanation: Material traceability is crucial for monitoring and tracing materials from their arrival through various production stages, ensuring quality and accountability.)

Q26. What role does a Third-Party Inspector play in the QC process?
  1. Conducts internal audits
  2. Represents the manufacturing company
  3. Provides an unbiased assessment
  4. Handles employee relations

(Explanation: A Third-Party Inspector offers an impartial evaluation of products or processes, ensuring objectivity in quality control assessments.)

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Q27. What does the material specification SA516 Gr 60 refer to?
  1. A type of stainless steel alloy
  2. A specific grade of carbon steel for pressure vessel applications
  3. An aluminum alloy commonly used in structural applications
  4. A high-strength titanium alloy

(Explanation: SA516 Gr 60 is a carbon steel grade specifically designed for pressure vessel applications due to its excellent weldability and toughness properties, making it ideal for withstanding high-pressure environments.)

Q28. How do SS304 and SS304L differ in terms of carbon content?
  1. SS304 is magnetic, while SS304L is non-magnetic
  2. SS304 has a higher carbon content than SS304L
  3. SS304L is more resistant to corrosion than SS304
  4. SS304 has a lower chromium content compared to SS304L

(Explanation: The main difference between SS304 and SS304L lies in their carbon content, with SS304 having a higher carbon content than SS304L, impacting their respective properties and applications.)

Q29. Why is SA516 Gr 60 commonly used in pressure vessel fabrication?
  1. Due to its high resistance to corrosion
  2. Because of its excellent weldability and toughness properties
  3. For its lightweight characteristics
  4. For its high thermal conductivity

(Explanation: SA516 Gr 60 is favored in pressure vessel fabrication for its exceptional weldability and toughness, ensuring reliable performance under high-pressure conditions.)

Q30. What advantage does SS304L offer over SS304?
  1. Higher strength and hardness
  2. Improved resistance to intergranular corrosion
  3. Greater ductility and toughness
  4. Enhanced thermal conductivity

(Explanation: SS304L provides enhanced resistance to intergranular corrosion compared to SS304, making it suitable for applications where corrosion resistance is critical.)

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Q31. What specific elements are controlled in the chemical composition of SA516 Gr 60 to meet pressure vessel requirements?
  1. Carbon, manganese, and silicon
  2. Chromium, nickel, and molybdenum
  3. Phosphorus, sulfur, and copper
  4. Aluminum, titanium, and vanadium

(Explanation: SA516 Gr 60 requires precise control of carbon for strength, manganese for toughness, and silicon for deoxidation in pressure vessel applications. These elements contribute to the material’s mechanical properties and resistance to pressure-related stresses. www.weldingandndt.com)

Q32. In SS304, what role does the chromium content play in enhancing its corrosion resistance properties?
  1. Chromium increases hardness and strength
  2. Chromium forms a passive oxide layer for corrosion protection
  3. Chromium improves ductility and toughness
  4. Chromium enhances thermal conductivity

(Explanation: The chromium content in SS304 enables the formation of a passive oxide layer on the surface, providing excellent corrosion resistance by preventing direct contact of the base metal with corrosive environments.)

Q33. How does the carbon content difference between SS304 and SS304L impact their weldability characteristics?
  1. Higher carbon content improves weld penetration
  2. Lower carbon content reduces the risk of carbide precipitation
  3. Carbon content has no effect on weldability
  4. Carbon content influences heat-affected zone properties

(Explanation: SS304L’s lower carbon content minimizes carbide precipitation during welding, reducing the susceptibility to intergranular corrosion and enhancing weldability compared to SS304. www.weldingandndt.com)

Q34. What mechanical property is crucial for SA516 Gr 60 in pressure vessel applications?
  1. Yield strength
  2. Hardness
  3. Elongation
  4. Impact toughness

(Explanation: Impact toughness is vital for SA516 Gr 60 in pressure vessels to withstand sudden loading conditions without fracturing, ensuring structural integrity and safety under varying stress levels.)

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Q35. Why is SS304 preferred over SS304L in certain high-temperature applications despite SS304L’s improved corrosion resistance?
  1. SS304 offers better thermal conductivity
  2. SS304 has higher strength at elevated temperatures
  3. SS304L is prone to sensitization at high temperatures
  4. SS304 provides superior resistance to thermal expansion

(Explanation: Sensitization in stainless steel like SS304L refers to a process where chromium carbides form along the grain boundaries when exposed to high temperatures, reducing the chromium available to form the protective passive oxide layer. This leads to a depletion of chromium near the grain boundaries, making the material susceptible to intergranular corrosion. In high-temperature environments, this sensitization phenomenon can compromise the corrosion resistance of SS304L, making SS304 a more suitable choice despite its slightly lower resistance to corrosion. www.weldingandndt.com)

Q36. What is the Heat-Affected Zone (HAZ)? www.weldingandndt.com
  1. The area that melts during welding
  2. The area of the base metal adjacent to the weld that does not melt but undergoes microstructural changes due to heat
  3. The area outside the weld
  4. The area where the weld metal is applied

(Explanation: The Heat-Affected Zone (HAZ) is the part of the base metal near the weld that gets heated and change its internal structure but doesn’t melt. During welding, the intense heat from the welding process is concentrated at the joint, causing the base metal in this region to reach high temperatures. Although the HAZ does not melt, the heat is sufficient to alter the microstructure and properties of the metal. This change in the metal’s internal structure can affect its strength, hardness, and other characteristics. www.weldingandndt.com)

Q37. What is the minimum specified tensile strength of ASME SA 516 Gr. 70? www.weldingandndt.com
  1. 70 Mpa
  2. 70 Psi
  3. 70000 Psi
  4. 60 Ksi
  5. 700 Mpa

(Explanation: As per ASME Section II Part A, the tensile strength for SA 516 Gr. 70 is between 70 Ksi to 90 Ksi [485 Mpa – 620 Mpa]. Thus, the minimum tensile strength is 70 ksi (which is equivalent to 70,000 psi or 485 MPa www.weldingandndt.com)

Q38. What is the minimum required retention period for Procedure Qualification Records (PQRs) and Welder Performance Qualifications (WPQs) according to ASME Section IX? www.weldingandndt.com
  1. Six months or till the completion of the projects
  2. Not specified in ASME Section IX
  3. Five years
  4. Three months

(Explanation: www.weldingandndt.com According to Clause 103.2 of ASME Section IX, it is stated that records must be maintained. However, the code does not specify a minimum or maximum duration for how long these records should be kept.)

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Q39. How long is a welder’s qualification valid if they haven’t done any welding with the process they have qualified to, as per ASME Section IX?
(www.weldingandndt.com)
  1. 3 months
  2. 6 months
  3. 2 year
  4. Not specified in ASME Section IX

(Explanation: As per QW-322.1, According to QW-322.1, a welder’s qualification is valid for 6 months after they last used that welding process. If they don’t use it within that time, the qualification expires.)

Q40. During welder qualification test on a pipe, which area is to be visually inspected as per ASME section IX? 
(www.weldingandndt.com)
  1. Only root side to check the penetration
  2. Entire circumference, inside and outside
  3. Only outside if radiography is to be done
  4. Only the face and root of the weld
  5. Both 1 & 3

(Explanation: As per QW-302.4, during a welder qualification test on a pipe, the entire circumference of the weld, both inside and outside, must be visually inspected.)

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Q41. A radiography test revealed a 10 mm lack of penetration (inadequate penetration without high-low) in a weld. According to API 1104, is this acceptable? (www.weldingandndt.com)
  1. Yes, it is acceptable
  2. No, it exceeds the limit
  3. Only if the aggregate length is within limits
  4. It depends on the project specifications

(Explanation: The acceptance criteria for inadequate penetration without high-low are outlined in Clause 9.3.1 of API 1104. The key points are as follows:

    • An individual indication of inadequate penetration must not exceed 1 inch (25 mm).
    • The total length of indications in any continuous 12-inch (300 mm) section of weld should not exceed 1 inch (25 mm).
    • For welds shorter than 12 inches, the aggregate length of indications should not exceed 8% of the total weld length.

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Analysis of the 10 mm Indication:
    • A 10 mm lack of penetration is less than the individual limit of 25 mm, making it acceptable based on that criterion.
    • As long as this indication does not contribute to exceeding other limits (like aggregate lengths), it would be considered acceptable under API 1104.)
Q42. What is buttering in welding?
  1. The process of applying a protective coating on metal surfaces.
  2. The addition of material, by welding, on one or both faces of a joint, prior to the preparation of the joint for final welding.
  3. A method for cooling welded joints to prevent cracking.
  4. The removal of excess weld material after the welding process is completed.

(Explanation: Buttering is a welding technique where extra material is added to one or both sides of a joint before the final weld is done. This extra layer helps create a smoother connection, making it easier for the final weld to hold together well. By doing this, it reduces the chances of problems like cracking or weak spots in the finished weld.

Q43. What is the main advantage of using Gas Metal Arc Welding (GMAW) over Shielded Metal Arc Welding (SMAW)?
(www.weldingandndt.com)
  1. GMAW requires no shielding gas.
  2. GMAW is generally faster and produces less smoke.
  3. GMAW can only be used on thin materials.
  4. GMAW is more suitable for outdoor applications.

(Explanation: Gas Metal Arc Welding (GMAW) is often preferred over Shielded Metal Arc Welding (SMAW) because it allows for continuous feeding of wire, resulting in faster welding speeds and reduced smoke production due to absence of flux. In contrast, SMAW uses fixed-length electrodes, which require the welder to replace the electrode once it is consumed. This process can be time-consuming and results in increased fumes due to the flux coating on the electrodes. Consequently, GMAW is often more time efficient and cleaner compared to SMAW.)

Q44. Which of the following is NOT a common non-destructive testing (NDT) method?
  1. Ultrasonic Testing (UT)
  2. Radiographic Testing (RT)
  3. Magnetic Particle Testing (MT)
  4. Sandblasting

(Explanation: NDT methods, such as Ultrasonic Testing (UT), Radiographic Testing (RT), and Magnetic Particle Testing (MT), are used to evaluate the integrity of materials without causing damage. Sandblasting, on the other hand, is a surface preparation technique that removes contaminants but does not assess material integrity.)

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Q45. In a stress-strain curve, what does the area under the curve represent?
  1. Elastic limit
  2. Yield strength
  3. Toughness
  4. Modulus of elasticity

(Explanation: In a stress-strain curve, the area under the curve represents toughness, which is the ability of a material to absorb energy before breaking. Essentially, it shows how much energy a material can handle while being stretched or compressed. The larger the area, the tougher the material is, meaning it can withstand more stress without failing. This is important for materials used in construction and manufacturing, as they need to be strong and flexible enough to endure various forces without breaking.)

Q46. What is the primary purpose of using expansion joints in piping systems? (www.weldingandndt.com)
  1. To allow for smooth transitions between different pipe materials
  2. To absorb vibrations from nearby machinery
  3. To prevent pipes from bursting during extreme temperature changes
  4. To provide a flexible connection that accommodates thermal expansion

(Explanation: Expansion joints are specifically designed to handle the expansion and contraction of piping due to temperature fluctuations, preventing stress and potential damage to the system. While options A, B, and C may seem relevant, they do not accurately represent the primary function of expansion joints in maintaining the integrity of piping systems.)

Q47. What is an example of a Quality Control (QC) technique?
  1. Developing marketing strategies
  2. Conducting non-destructive testing
  3. Training employees on new software
  4. Scheduling production timelines

(Explanation: Non-destructive testing (NDT) is a quality control technique used to check the material without causing damage. This method helps identify defects or irregularities in products, ensuring they meet quality standards. Unlike the other options listed, which focus more on planning or training, NDT directly assesses the quality of the product itself.)

Q48. What is the main difference between E6010 and E6013 electrodes?
  1. E6010 is for smooth bead appearance, E6013 is for deep penetration
  2. E6010 is for deep penetration, E6013 is for general-purpose welding
  3. Both are the same, just different names
  4. E6013 can replace E6010 in all cases

(Explanation: E6010 is a cellulosic electrode used for deep penetration and especially for root passes in pipelines and pressure vessels. E6013 is a rutile-coated electrode, used for general fabrication because it gives a smoother bead but with shallow penetration.)

Q49. Which filler wire is commonly used for MIG welding of mild steel?
  1. ER308L
  2. ER4043
  3. ER70S-6
  4. ER309L

(Explanation: ER70S-6 is the standard MIG filler wire for mild steel. It contains deoxidizers like manganese and silicon, which help in welding even on slightly rusty or dirty steel. People often get confused because ER308L (for stainless) and ER4043 (for aluminium) are also popular fillers, but they cannot be used for mild steel.)

Q50. Which filler metal is best for welding 304 stainless steel?
  1. ER70S-6
  2. ER308L
  3. ER4043
  4. E6013

(Explanation: ER308L is specifically designed for 304 stainless steel. The “L” means low carbon, which prevents carbide precipitation and keeps the weld resistant to corrosion.)

Q51. Which electrode is best for root pass welding in pipelines?
  1. E6013
  2. E6010
  3. E7018
  4. ER70S-6

(Explanation: E6010 has a cellulosic coating, giving deep penetration and a forceful arc that cleans the joint as it welds. This makes it the go-to electrode for root passes in pipelines. E6013 or E7018 cannot achieve the same root penetration.)

Q52. Which filler wire is best for TIG welding aluminium?
  1. ER308L
  2. ER4043
  3. E7018
  4. ER70S-6

(Explanation: ER4043 is the most common filler for aluminium alloys because it flows easily and resists cracking. ER5356 is another option, but ER4043 is the first choice for beginners.)

Q53. Which filler metal should be used when welding stainless steel to mild steel?
  1. ER308L
  2. ER309L
  3. ER4043
  4. ER70S-6

(Explanation: ER309L is specially designed for dissimilar welding (joining stainless steel to mild steel). Using ER308L (for stainless-to-stainless) will result in cracking and weak joints. This is a very common mistake.).

Q54. Why is E7018 preferred for structural steel welding (bridges, buildings, etc.)?
  1. It is the cheapest electrode
  2. It has low spatter and easy slag removal
  3. It produces welds with high strength and low hydrogen
  4. It requires no storage care

(Explanation: E7018 is a low hydrogen, high-strength electrode, making it suitable for critical structures where cracking cannot be tolerated. Beginners often pick E6013 for ease of use, but E7018 gives far better mechanical properties.)

Q55. For MIG welding stainless steel, which shielding gas is normally used?
  1. 100% CO₂
  2. Argon + 2–5% CO₂
  3. 100% Argon
  4. Helium only

(Explanation: Stainless steel MIG welding requires an argon-rich gas with a small amount of CO₂ (2–5%). This prevents excessive oxidation while giving arc stability. Using 100% CO₂ will destroy corrosion resistance, and 100% Argon causes poor arc stability.)

Q56. Which test gives yield strength of material?
  1. Tensile test
  2. Bend test
  3. Impact test
  4. Hardness test

(Explanation: Tensile test gives yield strength, Ultimate tensile stress – UTS, and % elongation values.)

Q57. Which filler material is most suitable for welding Inconel to carbon steel?
  1. E7018
  2. ERNiCr-3
  3. ER316L
  4. E6013
  5. Both 2 and 3

(Explanation: Inconel (nickel-based alloy) to carbon steel requires nickel alloy fillers like ERNiCr-3 to prevent cracking and dilution problems. Using stainless steel fillers (like 316L) can cause weld failure.)

Q58. When reviewing a PQR for a new WPS, you note the carbon equivalent (CE) of the base steel is 0.45 %, but the WPS calls for using E7018 only and pre-heat of 50 °C. The thickness is 20 mm. The QA engineer should: 
  1. Approve it because E7018 is qualified.
  2. Ask for higher pre-heat because CE is high and thickness is 20 mm.
  3. Reject the WPS because CE >0.40 % always requires PWHT.
  4. Recommend changing to ER70S-2 filler instead of E7018.

(Explanation: The QA engineer should ask for higher preheat because the carbon equivalent (CE) of 0.45% and 20 mm thickness increase risk of weld cracking and HAZ hardening. E7018 is a suitable low-hydrogen electrode, but most of the internationally accepted codes/standards recommend increased preheat above 0.40% CE, and 50 °C may be inadequate for safe welding. Rejecting the WPS or switching to another filler is unnecessary provided WPS parameters are modified accordingly. To learn more about preheat, Please read: https://www.weldingandndt.com/preheating-how-when-and-why/).

Q59. Which of these consumables is least appropriate when welding 304L stainless steel piping in a refinery where chloride contamination is a problem?

  1. ER308L filler wire
  2. ER309L filler wire
  3. E308-16 stick electrode
  4. E316L stick electrode

(Explanation: The least appropriate consumable for welding 304L stainless steel piping in a chloride-contaminated refinery environment is ER308L filler wire (option a). Standard 304L (and its matching fillers ER308L/E308-16) are vulnerable to chloride-induced pitting and crevice corrosion, especially above 100 ppm chloride, a scenario often encountered in refinery applications. ER309L adds higher Cr and Ni, while E316L provides Mo for superior chloride resistance, making them better suited for such environments. Therefore, while ER308L is often used for general 304L welding, in high-chloride scenarios it is the least appropriate due to inadequate resistance to chloride attack.)

Q60. During post-weld heat treatment (PWHT) of an alloy steel header in a refinery at 620 °C for 4 hours, the thermocouples are placed but one falls off and isn’t reattached until 2 hours into the hold period. What is the correct QA/QC action?
  1. Accept the PWHT because the temperature was maintained for full 4 hours.
  2. Reject the part because thermocouple immobilization is mandatory.
  3. Continue, but extend the hold period by 2 hours to compensate.
  4. Consult the applicable code/specification whether lost thermocouple invalidates the treatment.

(Explanation: The best QA/QC action is option d) Consult the applicable code/specification whether lost thermocouple invalidates the treatment. Most codes require continuous temperature monitoring at critical locations during the entire PWHT hold period, and missing temperature records usually mean the treatment cannot be automatically accepted or extended without review. Depending on the code (such as ASME), the procedure may require repeating or extending the PWHT, but final acceptance or corrective actions should be made in accordance with specific code provisions and project requirements.)

Q61. If a WPS lists an inter-pass temperature not exceeding 200 °C, but actual inter-pass temperature reached 260 °C in a carbon steel weld, what is the likely impact and what should the QA/QC engineer consider?
  1. No impact – anything below 300 °C is safe.
  2. Possible grain growth in HAZ, toughness loss, so review impact test results and procedures.
  3. Must perform full PWHT immediately.
  4. It’s only relevant for stainless steels, not carbon steels.

(Explanation: Exceeding the WPS-specified maximum inter-pass temperature can lead to grain growth in the heat-affected zone (HAZ) and decreased toughness, especially for carbon steels. The QA/QC engineer should evaluate the mechanical properties, particularly impact toughness, and review whether the weld still meets code and specification requirements. It is important to follow the WPS strictly, as higher inter-pass temperatures can compromise weld quality and cause non-compliance with procedure qualifications.)

Q62. During welding of a boiler tube joint, the welder reports excessive porosity in the root pass. The base metal is SA-210 Gr A1, and electrode used is E7018. The most likely cause is:
  1. Incorrect electrode type
  2. Low heat input causing lack of fusion
  3. Moisture in electrode or improper baking
  4. Excessive interpass temperature

(Explanation: E7018 electrodes are low-hydrogen type and must be baked properly before use. If moisture is absorbed by flux, it releases hydrogen during welding, creating gas porosity. Re-baking and proper storage in a heated oven prevent this issue.)