To find a material's P#, you would need to look in ASME Boiler and Pressure Vessel Code Section IX table QW-422. I do not see either of the ASTM specs you listed in the table. (However, to be included in the table, it would need to be SA564 T630, or SA747 Gr. CB7Cu-1, as listed in the Boiler and Pressure Vessel Code part II.) If you are qualifying an unclassified base metal you need to do it according to QW-424 in Section IX.