P Numbers and S Numbers

See the following paragraphs extracted from ASME BPVC, Section IX:

QW-420 MATERIAL GROUPINGS

QW-420.1 P-Numbers and S-Numbers. Base metals have been assigned P-Numbers or S-Numbers for the purpose of reducing the number of welding and brazing procedure qualifications required. In addition, ferrous base metals have been assigned Group Numbers creating subsets of P-Numbers and S-Numbers that are used when WPS's are required to be qualified by impact testing by other Sections or Codes.

These assignments are based essentially on comparable base metal characteristics, such as composition, weldability, brazeability, and mechanical properties, where this can logically be done. These assignments do not imply that base metals may be indiscriminately substituted for a base metal that was used in the qualification test without consideration of compatibility from the standpoint of metallurgical properties, postweld heat treatment, design, mechanical properties, and service requirements.

QW-420.2 S-Numbers. S-Numbers are assigned to materials that are acceptable for use by the ASME B31 Code for Pressure Piping, or by selected Boiler and Pressure Vessel Code Cases, but which are not included within ASME Boiler and Pressure Vessel Code Material Specifications (Section II).

Material produced under an ASTM specification shall be considered to have the same S-Number or S-Number plus Group Number as that of the P-Number or P-Number plus Group Number assigned to the same grade or type material in the corresponding ASME specification (i.e., SA-240 Type 304 is assigned P-No. 8, Group No. 1; therefore, A 240 Type 304 is considered S-No. 8, Group No. 1).

QW/QB-422 FERROUS/NONFERROUS P-NUMBERS AND S-NUMBERS Grouping of Base Metals for Qualification

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