Determination of design pressure and design temperature for low-temperature pressure vessels

It is also necessary to consider whether it is a low-temperature and low-stress operating condition

The design pressure and design temperature of the equipment are determined based on its operating conditions and operating temperature

The design temperature, together with the design pressure, serves as part of the design load conditions, and both should be considered together. Values should be selected based on the actual operating conditions of the vessel; it is not appropriate to combine the most unfavorable pressure and temperature conditions that are unlikely to occur simultaneously. When unfavorable temperature and pressure conditions do not occur at the same time, they should be considered separately. The principles are as follows: (1) If the design temperature does not involve low temperatures, and both pressure and temperature vary during operation, then the design pressure and design temperature should be determined using the most unfavorable conditions. (2) If a pressure vessel operates under two different temperature and pressure conditions that do not overlap in time, the design temperature and design pressure should be specified for each operating condition separately; it is not correct to combine the unfavorable temperature from one condition with the unfavorable pressure from another condition as design parameters... Refer to Wang Fei, page 87

The design pressure for liquefied gases should be determined based on their saturated vapor pressure; this is clearly stated in the regulations.