(a) The maximum allowable working pressure for a vessel is the maximum pressure permissible at the top of the vessel in its normal operating position at the designated coincident temperature specified for that pressure. It is the least of the values found for maximum allowable working pressure for any of the essential parts of the vessel by the principles given in paragraph (b) of this section and adjusted for any difference in static head that may exist between the part considered and the top of the vessel. (See appendix 3 of Section VIII of the ASME BPVC (incorporated by reference; see § 54.01-1.))

(b) The maximum allowable working pressure for a vessel part is the maximum internal or external pressure, including the static head hereon, as determined by the rules and formulas in Section VIII of the ASME BPVC, together with the effect of any combination of loadings listed in UG-22 of Section VIII of the ASME BPVC (see § 54.01-30) that are likely to occur, or the designated coincident operating temperature, excluding any metal thickness specified as corrosion allowance. (See UG-25 of Section VIII of the ASME BPVC.)

(c) Maximum allowable working pressure may be determined for more than one designated operating temperature, using for each temperature the applicable allowable stress value.