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:
- Composition- C-Mn, C-Mo, Cr-Mo, etc.
- Mechanical Properties– Tensile & toughness
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-Numbers||Base Metal (Typical or Example)|
|1||Carbon Manganese Steels (four Group Numbers)|
|2||Not Used in ASME|
|3||Half Molybdenum or half Chromium, half Molybdenum (three Group Numbers)|
|4||One and a quarter Chromium, half Molybdenum (two Group Numbers)|
|5A||Two and a quarter Chromium, one Molybdenum|
|5B||Five Chromium, half Molybdenum or nine Chromium, one Molybdenum (two Group Numbers)|
|5C||Chromium, Molybdenum, Vanadium (five Group Numbers)|
|6||Martensitic Stainless Steels (Grade 410, 415, 429) (six Group Numbers)|
|7||Ferritic Stainless Steels (Grade 409, 430)|
|8||Austenitic 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, C||Two to four Nickel Steels|
|10A, B, C, F||Various low alloy steels|
|10H||Duplex and Super Duplex Stainless Steel (Grades 31803, 32750)|
|10I||High Chromium Stainless Steel|
|10J||High Chromium, Molybdenum Stainless Steel|
|10K||High Chromium, Molybdenum, Nickel Stainless Steel|
|11A||Various high strength low alloy steels (six Group Numbers)|
|11B||Various high strength low alloy steels (ten Group Numbers)|
|12 to 20||Not Used|
|21||High Aluminum content (1000 and 3000 series)|
|22||Aluminum (5000 series – 5052, 5454)|
|23||Aluminum (6000 series – 6061, 6063)|
|25||Aluminum (5000 series – 5083, 5086, 5456)|
|26 to 30||Not used|
|31||High Copper content|
|36 to 40||Not Used|
|41||High Nickel content|
|42||Nickel, Copper – (Monel 500)|
|43||Nickel, Chromium, Iron – (Inconel)|
|44||Nickel, Molybdenum – (Hastelloy B2, C22, C276, X)|
|46||Nickel, Chromium, Silicone|
|47||Nickel, Chromium, Tungsten|
|47 to 50||Not Used|
|51, 52, 53||Titanium Alloys|
|61, 62||Zirconium Alloys|
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.