How do I test a pressure vessel containing Hydrogen

[hjulien]

I,

one of our subcontractor has tested a pressure vessel with dry nitrogen at 1.1 times the MAWP. But the vessel will keep -40F dewpoint hydrogen at 300 PSIG MAWP. According to me this test is not enough because according to the table of element, the atomic Weight of N is 14 times higher than H.

What kind of test normally are you testing that kind of equipment? Do you think Helium (He) pneumatic test will be better? Can you give some references to help me to find out wich test is better?

Thanks in advance,

hjulien

 

[pmover]

by what code was the vessel constructed? recommend investigating the appropriate code for resolution.

lastly, test medium, depending upon code and/or client specs, usually is air, N2, or water.

Oh! pressure is pressure, independent of test medium used.

good luck!
-pmover

 

[SnTMan]

hjulien, Code required pressure tests are not intended to prove leak tightness in service. There are some other threads that address this issue in more detail. Try searching on hydrotest, etc.

Regards,

Mike

 

[hjulien]

pmover, to Code use is the Section VIII div.1 edition 2004 Addenda 2006. I cannot see anything about my issue in that Code.

Hjulien

 

[CodeRef]

Read this thread:

http://www.eng-tips.com

http://www.eng-tips.com/viewthread.cfm?qid=180845&page=1

I am sure there are other threads to read as well. Just use the search tools here in the forums.

Reference UG-99(g)(1) and UG-100(d)(1) of Section VIII, Division 1:

A suitable gas leak test, if applied as a substitution of the hydrotest is acceptable only by agreement reached between Manufacturer and Authorized Inspector.


There are three kinds of people in this world; those who can count and those who can't.

 

[dcasto]

I repeat myself on testing piping and vessels (except pipelines), that the tests are not mechanical strenght tests per se. The test will find certain welding flaws and fittings that are not made up correctly, it will not prove that the material is bad because the test only gets halfway to the materials yield strenght and the welding is even less tress tested. The hydrotest will find gross defects, a pin hole will not cause a vessel or line to fail catastrophically, just leak. (may indicate that you need a better supplier of vessels too)

As for the ops question, mole weight has nothing to do with a pressure test, OK if the vessel is 3000 meters tall then it does, but does have a bearing on a leak test. As the link points out, you can calculate losses through a leak based on molecule size and with that you can get a ECONOMIC impact or your leak because it is your business how much hydrogen you want to allow to leak. All bets are off for other gases that are harmfull, but again, even the EPA has allowances for leaks of harmfull materials.

So you pick the economics, a $10,000 helium test to prove you'll lose $39 worth of hydrogen a year is your economic choice, but it won't improve the safety of you vessel.

 

[EmilGies]

Wouldn't you want to incorporate the static head of the N2 into the calc for hydro test and then just use H2O for the test itself? I would suspect a slightly higher test pressure. Am I missing something very fundamental?

 

[dcasto]

Static head of Nitrogen gas? Insignificant.

 

[EmilGies]

Dcasto - I thought hydrogen but typed nitrogen. Regardless, you made an excellent point in your previous post. Sorry to clutter this thread.

I am not familiar with when you would want to use a N2 pressure test in stead of hydro test.

Again, sorry for my previous clutter.

 

[dcasto]

The default test is always water. The use of nitrogen, air, helium are the exceptions and here are the things I look at as exceptions.

Will left over water cause problems in the process, freezing, chemical reactions, fouling, corrosion.

Will the process cause problems the water. Was ther oil left in the vessel that would make the test water hard to dispose of or other chemicals.

Is water readily avaiable. Or could a compressed bottle of gas supply the small voulme required.

Can the work area be cleared enough to used a compressed gas, if not go back to water.

Does the equipment need to be inerted after the hydrotest before commisioning with the process, if so, skip the water since you'll be putting nitrogen in before the process fluids anyway.

I work mostly with cryogenic hydrocarbons and nitrogen is great because it keeps the water out and freeze ups during start up to nil and there is no air to purge, love it. Bring in a LIN truck that put up 3000 psi and vaporize to GIN.