The Code-allowable stresses are determined by the ASME Subcommittee on Materials and are listed in ASME Section II, Part D [8] of the B&PV Code. That organization also determines the allowable stress for the B31 Codes, although those stresses are not published in Section II. The basic rules for acceptance of new materials are contained in the “Guideline on the Approval of New Materials Under the ASME Boiler and Pressure Vessel Code” (found in Section II, Part D, Appendix 5) and in the similar requirements of B31.1, Appendix VI, “Approval of New Materials.”
The allowable stresses of carbon steel material are based on properties data provided to the Subcommittee from at least three heats of the material. The properties that must be included are the tensile and yield strengths at 100ºF (38ºC) intervals from room temperature to 100ºF (38ºC) above the maximum intended use temperature. Also, if the material is expected to be used in the time-dependent temperature range (that is, creep), creep rate and stress rupture data must be included starting at approximately 50ºF (10ºC) below the temperature at which the time-dependent properties might govern to 100ºF (38ºC) above the maximum use temperature. Duration of at least 6000 hours is required for the creep rupture tests.
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