Hydrogen Piping 2

[BobW2]

Should unions be avoided in a hydrogen piping system?
Even though my application is low pressure <50 psig, I still want to adhere to industry standard practice.

 

[Montemayor]

BobW2:

Hydrogen is the smallest molecule in the Cosmos, from a practical point of view. It will permeate through your steel pipe, albeit slowly. Every plant pipe standard I've worked under and also written has specified a minimum of only flanged connections - with special gaskets. In a practical sense, I consider 100% butt-welded & radiographed piping as the best solution. All the Hydrogen that I've transported has been of a purity exceeding 90% by volume and, as such, devoid of requiring a means to disassemble the piping for maintenance or inspection. Is your H2 of the same quality? If so, that's what I would strongly urge you to do.

I wouldn't even think of permitting anyone to employ screwed fittings or pipe unions on Hydrogen service. I classify screwed fittings and pipe unions as plumbers tools. Experienced pipefitters will tell you the same and sneer at the mention of screwed fittings and pipe unions. The pipe union, in my opinion, was designed to leak water - much less to be applied in Hydrogen service. I consider it nothing less than a cruel joke in this application.

Again, any Hydrogen service is critical and as such deserves what I consider to be the safest installation with utmost mechanical integrity: 100% butt welded and radiographed (where possible).

I hope this experience helps.

Art Montemayor
Spring, TX

 

[JDistheWP]

Ask Joe on the chemical team

 

[25362]

See also, for example,

http://avt.inel.gov/pdf/hydrogen/h2station_appendixc.pdf.

Remember that the hydrogen molecule is the lightest in the universe (helium is smaller in volume but heavier). Because of that fact and also because it tends to dissociate into nascent H atoms (smallest in the universe) it permeates metals and diffuses the quickest of all molecules.

 

[davefitz]

see thread124-92325 for recommendations on H2 piping

 

[jsummerfield]

What Art Montemayor and others said. Also, minimize the use of unions and threaded pipe on hydrocarbon service.


John

 

[iainuts]

Although welded pipe is generally desireable, one always needs to be able to disassemble the pipe, including maintenance on valves. I work for a major industrial gas company designing hydrogen piping from cryogenic to ambient and at pressures to 18,000 psi. For your application, I'd suggest O-ring unions such as CPV unions for disassembly purposes on small pipe (ie: aprox. 2" and smaller) and flanges on larger pipe.

Also, the leakage from seals such as these will be bubble tight, but will still be many orders of magnitude higher than any 'leakage' through the metal wall. I wouldn't even consider any special precautions because of possible leakage through metal. That leakage is on a quantum level.

Have you considered using tube? For many applications, say 1" or smaller at lower pressure, I'd suggest duel ferrul (ie: Swagelok/Parker A-Lok/Bilok etc...) or 37 degree flared fittings.