To reduce the number of welding and brazing procedure qualifications required base metals have been assigned P-Numbers by the ASME BPVC.Ferrous metals which have specified impact test requirements have been assigned Group Numbers within P-Numbers.
These assignments have been based on comparable base metal characteristics, such as:
Composition
Weldability
Brazeability
Mechanical Properties
Indiscriminant substitution of materials in a set of P-Numbers or Group Numbers may lead to problems or potentially failures.Engineering assessment is necessary prior to a change in materials.
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 P-Number.
The table below is a guide and is for instructive purposes only. 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 only a rather incomplete and approximate summary of ASME data.
P-Numbers
Base Metal (Typical or Example)
1
Carbon Manganese Steels (four Group Numbers)
2
Not Used
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)
