P Number, F Number and A Number in welding (ASME Section IX)

ASME Boiler and pressure vessel code (BPVC) has assigned certain numbers to base metals as well as to filler metals (electrodes).

For base metals, ASME has assigned two number system, these are;

  • P Numbers
  • Group Numbers

For filler metals, the number system which are assigned, are as follows;

  • F Number
  • A Number

These numbers can be found in ASME BPVC Section IX (2017 edition), please see table – 1 for details;

Table – 1 

BASE METAL GROUPING:

Main purpose of assigning this number system is to reduce the number of procedure qualification records (PQR). Conducting a procedure qualification requires a lot of time and money due to the following procedural requirements;

  • Preparation of test coupon
  • welding of test coupon and
  • sending it to lab for destructive test

Hence, to reduce these costly and time consuming activities, ASME has done grouping of base metals and has assigned certain P numbers to each group of metals. This grouping of base metals has been done on the basis of the following parameters;

  • Material composition
  • Weldability
  • Mechanical property

Though all materials of same ‘P’ number doesn’t exhibit the same properties, but after considering the above mentioned parameters, ASME has done this logical grouping.

Why this grouping is required?

Suppose, if we change the base metal from an existing qualified WPS and if the new base metal falls in the same ‘P’ number then requalification of the existing WPS is not required, it means no need of a new PQR.

But this doesn’t mean that one can easily substitute the base material, from existing WPS, of same ‘P’ number at any time. Whenever there is a change in the base material from existing WPS, the compatibility shall be considered with regards to the following factors;

  • Metallurgical property
  • Mechanical property
  • Design considerations
  • Service requirements
  • Heat treatment

Table – 2 shows the assignment groups for various metals and its alloys (according to ASME BPVC, 2017 edition).

Table – 2

Now that we have understood ‘P’ numbers let’s move on to group numbers. Group numbers are subsets of ‘P’ numbers assigned to ferrous based metals. Group numbers are assigned only to those materials which requires toughness testing for the qualification of its WPS.

We will take an example of SA516 Gr 65 from table QW/QB-422 (Page – 118), we can find out the following values;

Base material – SA516 Gr 65

  • Tensile strength (min.) – 65 Ksi (or 450 Mpa)
  • P-No. – 1
  • Group number – 1
  • Nominal composition – C-Mn-Si
  • Typical product form – Plate

Another grouping of base metals was the ‘S’ numbers, but ‘S’ number is not used nowadays. It was deleted from ASME in 2009.

S Numbers were assigned to those materials which were acceptable for use by the ASME B31 Code for Pressure Piping, or by selected Boiler and Pressure Vessel Code Cases, but were not included in section II of ASME Boiler and Pressure Vessel (BPVC). Base metals which were previously assigned ‘S’ Numbers were reassigned the corresponding P Numbers or P Numbers and Group Numbers.

FILLER METAL (ELECTRODE/WELDING ROD) GROUPING:

The F Number: F number grouping (for filler metals) is done to reduce the number of welding procedure specification (WPS) and welder performance qualifications. Basis for F number grouping is usability characteristics. The usability characteristics fundamentally determines the ability of a welder to produce sound welds with a given filler metal. Hence it is assumed if a welder can make satisfactory weld with a particular filler metal, he will be able to weld with all the filler metals belonging to that particular ‘F’ number.

Table-3 shows a brief summary of ‘F’ and filler filler metals (according to ASME BPVC 2017 edition, Table – QW-432).

Table – 3

The ‘F’ number grouping doesn’t imply that one can easily substitute the filler metal (electrode/welding rod), from existing WPS, of same ‘F’ number at any time. Whenever there is a change in the filler metal (electrode/welding rod) from existing WPS, the compatibility shall be considered with regards to the following factors;

  • Metallurgical property
  • Mechanical property
  • Design considerations
  • Service requirements
  • Heat treatment 

The A Number: Another type of grouping for filler metal or welding rod is the ‘A’ Number. ‘A’ number grouping has been done on the basis of the chemical composition of the deposited weld metal. This can be found in ASME BPVC Section IX 2017 edition, Table – QW-442).

Also read: Thickness range for welder qualification

Also read: Welding Symbols

Also read: How to write a welding procedure specification

Also read: CSWIP Question Answers

Also read: Welding Electrodes/Filler metal

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