What is the relationship between the design pressure of a pressure vessel and its maximum allowable operating pressure?
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Recently, I saw a pressure vessel with an operating pressure of 0.1 MPa, a design pressure of 0.5 MPa, a maximum allowable operating pressure of 0.8 MPa, and a safety valve setting pressure of 0.6 MPa. I would like to ask what the relationship is between the maximum allowable operating pressure and the design pressure. Why are both the setting pressure of the safety valve and the maximum allowable operating pressure higher than the design pressure? The other party explained that we required a leak test, and in order to carry out this test, the setting pressure of the safety valve was set at 0.6 MPa, which is higher than the design pressure. What is the relationship between pressure vessel airtightness tests conducted in the manufacturing plant and safety valves? After talking about it for so long, we still haven’t clarified it.
That’s right; according to Appendix B of GB/T150-2011, the design pressure should be ≥ the set pressure, which in turn should be 1.05–1.1 times the operating pressure. However, when a leak test is required, per GB/T150-2011, the pressure used for the leak test is equal to the design pressure. TSG21-2016 stipulates that safety accessories must be fully installed when conducting a leak test. In such a situation, if the set pressure is equal to the design pressure, the safety valve will activate during the leak test, making it impossible to carry out the test. Therefore, it is necessary to specify the maximum allowable operating pressure of the container; this maximum allowable operating pressure must be greater than the set pressure and greater than the design pressure, in order to conduct a leak test. Alternatively, an ammonia leakage test can be conducted; the design can be carried out based on a design pressure ≥ set pressure ≥ 1.05–1.1 times the operating pressure
One can take a look at the definition of the maximum allowable operating pressure; it is determined by calculating based on the loads that each pressure-bearing component must withstand, and the maximum allowable operating pressure is greater than or equal to the design pressure.
When a device equipped with a safety relief mechanism (i.e., a safety valve) also requires a gas-tightness test, the relevant standards require that the maximum allowable operating pressure of the device be specified. During the gas-tightness test, the test pressure is set at the design pressure; however, to ensure the safety of the device – given that all necessary safety accessories are in place – the setting pressure of the safety valve is increased to a value not exceeding the device’s maximum allowable operating pressure.
I’ve encountered this situation; some manufacturing plants conduct airtightness tests without using safety valves. As a result, the setting pressure of these safety valves is sometimes lower than the designed pressure, but strictly speaking, this is not in compliance with standards
There is no comparability; the maximum allowable operating pressure can be lower than the design pressure.
Put simply, the design pressure is set in advance, while the maximum allowable pressure is determined through calculations. The set pressure of the safety valve shall not be higher than the design pressure or the maximum allowable pressure. Pressure resistance test: hydraulic test, pneumatic test, combined hydraulic-pneumatic pressure test (approximately 1.25 times the design pressure for hydraulic testing, and approximately 1.1 times the design pressure for combined hydraulic-pneumatic testing; the specific pressure for regular inspections is determined as per relevant standards). Leakage test: airtightness test (at design pressure), ammonia leak detection, etc.