Is it better to perform an air tightness test or a helium leak test for a hydrogen buffer tank?
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When I was designing a hydrogen buffer tank (design pressure 1.98MPa, design temperature 60°), in addition to the pressure test, I also required a leakage test. The test medium I wrote used dry air, and the test pressure was 1.98MPa. However, the superior leader's review opinion was to use helium for leak detection. The statement given was that if airtight was selected, the maximum allowable working pressure would need to be given, and the set pressure of the safety valve should be greater than the design pressure. I don't quite understand this comment. GB150 says that the set pressure of a safety valve is generally 1.05 to 1.1 times the working pressure, and the design pressure of the container is equal to or greater than the set pressure. Then I take 1.1 times as equal to the design pressure. Why does the superior say that the set pressure of the safety valve should be greater than the design pressure?
Because the pressure of the leakage test = design pressure, and all safety accessories are installed, if the set pressure < design pressure, then doesn’t the safety valve take off in advance? Of course, when there is no leakage test, it is a super-strength test, that is, pressure test > design pressure, and there is no need to install safety accessories at this time. The natural safety valve setting pressure should be set at 1.05 to 1.1 times the working pressure.
The problem mentioned by the leader is easy to solve, but in addition to giving the MAWP, you also need to recalculate the equipment strength. There seem to be two popular methods for setting the pressure of safety valves.: One is that the set pressure is higher than the design pressure and lower than the MAWP, so that it will not jump during the air tightness test. ； The other is to adjust the setting pressure of the safety valve to the pressure of the first method during the air tightness test. After passing the air tightness test, adjust the setting pressure back to between the working pressure and the design pressure. Another problem is that manufacturers often do not equip safety valves. In addition to the questions raised by the leaders, the permeability of hydrogen is significantly higher than that of air, so using air does not mean that hydrogen is also a problem. There is no official explanation for this problem, and we do not know who has stronger permeability and who has weaker permeability. Does using helium to detect leaks mean that there is no problem?
The set pressure of the safety valve must be inspected by the local supervisor every time it is adjusted, and it can only be used after passing the test. This also virtually increases the cost and cycle. Because when there is a pressure higher than the design pressure, there will also be a maximum allowable working pressure greater than the design pressure. It is not a contradiction that the safety valve setting pressure is greater than the design pressure.
If I choose to use helium for the leak test, the design pressure is 1.98 and the leak test pressure is 1.98, right? What is the appropriate set pressure for the safety valve?
Don't dare to set the pressure higher. If you are not careful, the pressure will go up to 2.0. Maybe the thickness of the equipment is not enough. Is it appropriate to set 1.99?
Helium leak detection and air tightness testing are different. You can refer to HG/T20584
OK, thanks! I'll check the specifications first
During the air tightness test, safety accessories (safety valves are also brought to prevent the pressure of the air tightness test from being too high than the design pressure, causing danger). Sometimes it is difficult to count the diameter of the safety valve for some media. The safety valve cannot have an elbow, otherwise it will be treated as a pipe leading out, and it will be regarded as a safety valve in the pipeline system.