Some questions regarding the set pressure and maximum allowable operating pressure of safety valves~
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In our current projects, the set pressure for safety valves is sometimes the design pressure of the equipment, and sometimes it is the maximum allowable operating pressure, That is, MAWP. If it is the design pressure, then there’s no problem, but if it is MAWP, I find it a bit difficult to understand. The problem is that the MAWP is calculated based on the wall thickness of the equipment (please correct me if I’m wrong, seniors). It is higher than the design pressure of the equipment, and can also be considered as the equipment’s maximum pressure. So, wouldn’t it be very dangerous to set the safety valve at such a high level? Moreover, the safety valve also needs to take overpressure into account. Furthermore, high demands are placed on the piping system; the pipes even require an increase in their design pressure to MAWP. Could someone with experience in safety valves give some advice? Thank you!
Look at HG/T 20570.2 and you’ll understand. It goes without saying that the set pressure of the safety valve must be less than or equal to the design pressure of the equipment.
The relationship among the three pressures: design pressure is greater than maximum operating pressure, which is in turn greater than the set pressure of the safety valve.
You are right; the maximum operating pressure is less than the design pressure, that is, the highest value that may occur during operation, and it is commonly referred to as Max. Pressure. But the maximum allowable operating pressure is not that; it is higher than the design pressure. It is the limit value for container design. MAWP, which stands for Maximum allowable working pressure.
What was said upstairs is correct; the pressure should increase from low to high as follows: container operating pressure = container return pressure