The contradiction between design pressure and safety valve setting pressure in standard specifications

The experts seem to have different opinions!

I don’t understand; just saying something random: Are the two referring to different safety valves? The pressure rating specifies the temporary safety valve used for pressure testing ； GB150.1 specifies permanent safety valves to be used during the operation of the equipment.

During the last certification process, the drawings submitted for review showed that the set pressure was higher than the design pressure but lower than the maximum allowable operating pressure. The experts immediately pointed out that this was a serious error, as the set pressure must never be higher than the design pressure. I think modifying the above sentence will make it correct: the set pressure must not be higher than the design pressure at any time (when there is a maximum allowable operating pressure, this shall replace the design pressure). This way, there’s no contradiction at any time, not even during the airtightness test.

This post was last edited by zjq1962 on 2019-1-3 at 16:18. I’m not sure under what circumstances the expert made that statement; in my opinion, there is no problem with the design. The last sentence in the attached diagram provides the best explanation. The diagram comes from Appendix B of GB/T150.1 – not only is the setting pressure used, but the test pressure for the pressure resistance test is also determined based on the maximum allowable operating pressure rather than the design pressure.

Appendix B B.3.1 When the pattern indicates the maximum allowable operating pressure, this may be used in place of the design pressure for the container’s maximum allowable operating pressure; the same applies hereafter. At first, I had the same doubt. This expert is amazing: lol

Article 3.1.18: For vessels equipped with safety valves and subject to a gas-tightness test, the design documents shall specify the maximum allowable operating pressure for such pressure vessels. This case is a special situation. The setting pressure can be higher than the design pressure, but it must not exceed the maximum allowable operating pressure; I confirmed this with the instructor during the last training session. In all other cases, the set pressure must be less than or equal to the design pressure.

Most importantly, I run into half-baked experts who can’t explain things clearly. Some experts in manufacturing don’t understand design, so they just stick strictly to the regulations. It’s not a complete understanding of the standards. Experts in design often mention that an effective thickness greater than twice the calculated thickness eliminates the need for reinforcement calculations due to openings. I often encounter experts who ask me to find the relevant provisions in GB/T150; if they are not from GB/T150, they refuse to acknowledge them.

This post was last edited by zjq1962 on 2019-1-4 at 08:20. When the effective thickness is more than twice the calculated thickness, it can be concluded that the hole reinforcement will definitely be satisfactory without the need for additional reinforcing elements; this can serve as a method for designers to make judgments, but it does not exempt the need for calculations related to hole reinforcement.

Yes, I also pay attention to this sentence. But perhaps we are all misunderstanding or there is a deviation. The original meaning here is that the maximum allowable operating pressure can be used as the design pressure. At this point, the design pressure changes. Then, the safety valve opens; its operating pressure must not be higher than the design pressure (in this case, it refers to the new design pressure after replacement), and this is mandatory, with no other conditions or additional explanations. So the question returns to its original point. In reality, it is known that many manufacturers close the valves during airtightness tests and seal the outlets with plugs, so that the system will not activate even when the pressure exceeds the design value. It feels like the standards are unclear and cannot guide practice, while practice is completely detached from those standards.

1. The starting point for the maximum allowable operating pressure specified in the tolerance standards is indeed the airtightness test. Because the regulatory standards specify that safety accessories generally need to be installed fully when conducting a leak test (although this is not mandatory). With this regulation in place, if the set pressure is still required to be no greater than the design pressure, theoretically, the test cannot be carried out. 2. The fact that the manufacturing unit did not install safety accessories during the airtightness test cannot be used as evidence of non-compliance with standards; the design must still determine the maximum allowable operating pressure in accordance with the regulations. 3. By specifying a maximum allowable operating pressure and increasing the set pressure, it is advantageous from a process perspective for ensuring stable operation.