Questions regarding the design pressure and design temperature of liquid oxygen
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I never expected to encounter this problem after working for so many years; filling out a pipeline property table proved to be difficult. Operating temperature, operating pressure, design temperature, design pressure. The operating temperature and operating pressure are corresponding to each other; the values filled in are -143 degrees and 1.6 MPa. However, I’m not sure how to fill in the design pressure and design temperature. The lowest temperature of the container occurs at normal pressure, and that temperature is -196 degrees. However, when the pressure is 2 MPa, the temperature is -143 degrees. Clearly, there is no one-to-one correspondence between 2 MPa and -196 degrees. Can it be filled in this way? A long time ago, during a design review, the special inspection agency pointed out that there was no one-to-one correspondence between temperature and pressure:
I understand your concern; this issue is indeed easy to cause confusion. The design temperature and design pressure do not need to correspond one-to-one with the operating parameters; instead, it is necessary to consider the highest/lowest temperature and pressure combinations that may occur simultaneously under all possible conditions of the pipeline or vessel, such as normal operation, abnormal operation, shutdown, or purging. For example, the \"minimum temperature of -196°C\" you mentioned is usually referred to under normal or low pressure; since the pressure is very low in such conditions, it isn’t necessary to use 2 MPa as the pressure value associated with -196°C ； The design temperature corresponding to a design pressure of 2 MPa should be the most unfavorable temperature that may occur at that pressure (it could be the operating temperature of -143°C, or some other higher temperature). It is recommended that you consult the definitions of \"design conditions\" in GB/T 20801 or ASME B31.3, or directly ask the pressure vessel design engineers at your organization – they are better aware of how to select the most stringent paired parameters. If the Special Inspection Agency has any objections, it is best to fill out the form in accordance with the standards they approve, to avoid having to redo the work. Hope this is a little helpful to you~