Why Helium Leak Test is Required for Hydrogen Services?

Think about it. Think about it carefully. If the equipment is under test and some part fails the test due to a leak, what would be the preferable fluid that leaks:

• Hydrogen, which is flammable, or
• Helium, which is not flammable

eh?

https://en.wikipedia.org/wiki/Hindenburg_disaster

Molecular size is important too. I think helium is smaller than H2 (stable hydrogen). Plus, I think helium is easy to detect with handheld devices.

Drew K

Hydrogen is very easy to detect with small handheld devices.

About 20 years ago I was giving a verbal test to someone who wanted to use LPG in an lunchwagon and needed to pass the test.

The final question that I asked was "After connecting the tank(of LPG) how would you determine if the connection was not leaking?"

Due to what I thought was a language barrier he couldn't answer, so I repeated the question using slightly simpler wording.

His answer: "Use a match?" He obviously failed, and that's why there were no further questions.

BTW at that time my daughters about 5 and 9 years old would come out with their bubble soap whenever I connected a new tank to the gas barbecue grille we had.

Not being snarky, just that your reply brought up a long forgotten memory.

Well, no snarkiness taken as my post was intended to be tongue-in-cheek.

(from memory) I believe it depends on the industry and application, some still allow flammable process gasses to be use for blow downs in piping systems (eg-natural gas).

HOWEVER this has caused a number of near misses and deadly explosions and I am not aware of any industries or systems where hydrogen is compulsory over an inert substitute such as helium (perhaps if the system was a fully closed loop system).

Perhaps some very specialised systems allow hydrogen leak testing, but you would need to check the standards regarding this and they should clearly indicate such and describe how it is to be done safely in the event inert gas leakage .

What's the application exactly?

I would also cite the wide range over which hydrogen flashes (4-98%?)as well as the fact that a hydrogen flame is almost invisible.

I believe it was 4% LEL and 96% UEL.

We had to do testing with silver-zinc battery housings (pressure vessels) to make sure we had a good nitrogen purge of the evolved hydrogen and oxygen. Used O2 sensors from MSA and flammable gas sensors from Crowcon Detection Inst.

We used hydrogen when we were characterizing the purge system. The safety people were going all bonkers over this. The irony was on the other side of the high bay, there was a welding room with oxygen acetylene tanks. Way more dangerous than the hydrogen. But as soon as you request use of hydrogen, all you get are "oh, the humanity" knee-jerk reactions. We had to have our company fire marshall present for all tests.

We never did helium tests for hydrogen. I've seen helium tests for silane but that is much worse than hydrogen. If you're indoors it might be a different animal but outdoors that seems like overkill. Test with nitrogen and soapy water for flanges and other equipment that was gotten into and be done with it.