What is P-Number in Welding and ASME?

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What is P-Number in Welding?

To reduce the number of welding and brazing procedure qualifications required base metals have been assigned P-Numbers (P mean Parent Metal) by the ASME codes.  Ferrous metals which have specified impact test requirements have been assigned Group Numbers within P-Numbers as given in Table QW/QB- 422 of ASME Section IX. These base metals are grouped by material and assigned P Numbers based on what material they are. For example, P Number 1 is assigned to Carbon Manganese or Low Carbon Steel base metals.

P-Number is an Essential variable for Welding Procedure Qualification according to ASME Section IX.

Assignments of P-Numbers have been based on similar base metal mechanical & chemical properties, for example:

When a base metal with a UNS number Designation is assigned a P-Number, then a base metal listed in a different ASME material specification with the same UNS number shall be considered that same P-Number.

The table below is a guide for current ASME P-Numbers material identification.  Anyone specifying materials or requirements should refer directly to the ASME Boiler and Pressure Vessel Code to specify materials, P-Numbers, procedures, or other requirements and not rely on the table below.  The table below is for reference and a ROUGH summary of ASME data for INSTRUCTIONAL USE ONLY.  See ASME Boiler and Pressure Vessel Code for materials specifications and P-Numbers. 

P-NumbersBase Metal (Typical or Example)
1Carbon Manganese Steels (four Group Numbers)
2Not Used in ASME
3Half Molybdenum or half Chromium, half Molybdenum (three Group Numbers)
4One and a quarter Chromium, half Molybdenum (two Group Numbers)
5ATwo and a quarter Chromium, one Molybdenum
5BFive Chromium, half Molybdenum or nine Chromium, one Molybdenum (two Group Numbers)
5CChromium, Molybdenum, Vanadium (five Group Numbers)
6Martensitic Stainless Steels (Grade 410, 415, 429) (six Group Numbers)
7Ferritic Stainless Steels (Grade 409, 430)
8Austenitic Stainless Steels·            Group 1 – Grades 304, 316, 317, 347·            Group 2 – Grades 309, 310·            Group 3 – High Manganese Grades·            Group 4 – High Molybdenum Grades
9A, B, CTwo to four Nickel Steels
10A, B, C, FVarious low alloy steels
10HDuplex and Super Duplex Stainless Steel (Grades 31803, 32750)
10IHigh Chromium Stainless Steel
10JHigh Chromium, Molybdenum Stainless Steel
10KHigh Chromium, Molybdenum, Nickel Stainless Steel
11AVarious high strength low alloy steels (six Group Numbers)
11BVarious high strength low alloy steels (ten Group Numbers)
12 to 20Not Used
21High Aluminum content (1000 and 3000 series)
22Aluminum (5000 series – 5052, 5454)
23Aluminum (6000 series – 6061, 6063)
24Not Used
25Aluminum (5000 series – 5083, 5086, 5456)
26 to 30Not used
31High Copper content
33Copper Silicone
34Copper Nickel
35Copper Aluminum
36 to 40Not Used
41High Nickel content
42Nickel, Copper – (Monel 500)
43Nickel, Chromium, Iron – (Inconel)
44Nickel, Molybdenum – (Hastelloy B2, C22, C276, X)
45Nickel, Chromium
46Nickel, Chromium, Silicone
47Nickel, Chromium, Tungsten
47 to 50Not Used
51, 52, 53Titanium Alloys
61, 62Zirconium Alloys

Click here to download ASME P-Number Table.pdf

Importance of P-Number

The P-Numbers help to reduce the range of WPS qualification requirements. For example, a WPS qualified with SA516 material which falls under P1 material can be used to weld any other material falling within the same P-Number. Below is a summary of material types based on P-Number according to ASME Section IX for welder qualification and procedure qualification.

Do all materials have a P-Number?

P numbers are specified in ASME Section IX and as we know ASME only covers materials that are used for the construction of boilers, pressure vessels, piping, nuclear, and related ASME code constructions.

So, not all of the materials will have the P-Numbers. 

What is S- Number

The S-Number was removed from ASME Section IX in 2009. The S Number’s purpose was identical to the P Number. However, these numbers were assigned to those materials included for pipework to the ASME B31 Code for Pressure Piping. These materials were also covered by the P-Number, but not the converse.

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