Using hydrogen for a gas-tightness test
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Our company’s specifications for the airtightness testing of the catalytic cracking unit state as follows: the airtightness levels are 0.4 MPa, 1.0 MPa, and 3.5 MPa for nitrogen testing, while 3.5 MPa, 5.0 MPa, 8.0 MPa, and 10.0 MPa for hydrogen testing. Since it’s a matter of airtightness, can’t we use nitrogen for all tests? Wouldn’t it be dangerous if there were a leak during hydrogen testing? If there are no leaks during the high-pressure nitrogen tests, then using hydrogen during normal operation would be much safer, right? Was the issue of pure hydrogen corrosion taken into account, which is why high-pressure airtightness testing with hydrogen was used? But the airtightness test lasts only for a short period of time; even if there is corrosion, it wouldn’t be detectable during that phase
Why can’t the pressure of nitrogen be set at 8.0 Mpa? It’s generally very difficult to achieve airtightness with hydrogen. If the compressor allows it, it’s better to raise the nitrogen pressure to 10 before reducing it to produce hydrogen
Seal integrity is tested using nitrogen and hydrogen at the same pressure level; if the test with nitrogen is successful, testing with hydrogen may yield a negative result. This is likely due to the different molecular structures of nitrogen and hydrogen, with hydrogen having the smallest molecular diameter.
According to construction standards, airtightness must be ensured; the use of nitrogen is not allowed, and hydrogen is even less permissible. This is because leaks in such cases can cause serious problems and lead to safety accidents. Your company might have two considerations: first, hydrogen has a low density; second, oxygen is not allowed in the pipelines. But there are no such pipes in the catalytic cracker unit. From this, it can be inferred that it must be the people in your company who developed the plan – they are too theoretical and too mechanical in their approach. It is recommended to stop the airtight operation and use dry air instead!
OP’s friend: I guess your boss came up with this desperate measure due to issues with the project progress; be careful.
For precision cracking and hydrogenation units, nitrogen must be used for airtightness testing before switching to hydrogen; air molecules have too high a molecular weight, so using it is pointless