The maximum and minimum design temperatures for a vessel will determine the maximum allowable stress value permitted for the material to be used in the fabrication of the vessel. The maximum temperature used in the design should not be less than the mean metal temperature expected under the design operating conditions. The minimum temperature used in the design should be the lowest expected in service except when lower temperatures are permitted by the rules of the ASME Code, In determining the minimum temperature, such factors as the lowest operating temperature, operational upset, auto-refrigeration, ambient temperature, and any other source of cooling should all be considered. If necessary, the metal temperature should be determined by computation using accepted heat transfer procedures or by measurement from equipment in service under equivalent operating conditions.
