Threadlocker/Sealant suitable for 6000psig Hydrogen re-fueling line

[Sherin Achenkunju]

Can someone help me to choose the right thread locker/sealant suitable for the 6000psig Hydrogen refueling line? The connections in this Hydrogen line are TIG welded (tubes to tubes)and Tube to devices (gas booster, storage cylinder, control valves) are parker triple-lok fittings. But still, NPT threaded connections are not avoidable in some cases. As this line involves tremendous vibration when re-fueling starts and ends, we are going to use sealant in NPT threaded joints. The supplier of the fittings suggested using a combination of Teflon tape and Loctite 542. But we are not sure as we don't have much experience in Hydrogen service lines. Hence I was seeking help from others, somebody instructed us to take care of the Autoignition temperature of Hydrogen (585 degree Celcius). Is anybody there to help me?

 

[TiCl4]

I can't comment on high-pressure thread lockers - we use cone&thread fittings for high pressure applications.

However, I would caution you that "tremendous vibration" and threaded fittings, especially small diameter threaded fittings with cantilevered loads (i.e. a pressure gauge port) do NOT play well together.

Why do you need to be worried about H2 autoignition? Do you have any way to get the H2 to that temperature? H2 expanding through a hole or leak will cool, not heat up...

 

[shvet]

As per my experience H2 leakages are prone to self ignition and are hard to be detected because of transparent flame.

 

[TiCl4]

Upon further research, below is a link that may explain some of the phenomenon. I was incorrect, previously - H2 apparently heats up upon expansion due to a "reverse" Joule-Thompson effect.

https://www.google.com/url?sa=t&rct...6bDxAhXITN8KHQ4DBJ8QFjALegQIIBAD&url=https://

http://www.hse.gov.uk/research/rrpdf/rr615.pdf&usg=AOvVaw0_q895yHoWa3HTb1YPMRW5

 

[bcd]

The two most secure options I know are either seal weld the pipe to the fitting, or X-pando pipe thread sealant.

 

[EdStainless]

You need to consider using fitting like your others that is threaded in and then seal welded.
You want to avoid NPT as they will eventually leak due to the profile.
We had a hydrogen manifold that ran at 5,000psi, we painted next to the joints (not over the potential leak path itself, after they were helium leak tested) with heat sensitive paint to allow early warning of leaks.
Yes, at that pressure and ambient temp you are in the regime there H2 will heat on expansion (He does this also).

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P.E. Metallurgy, consulting work welcomed