Pressure testing of PE lined Carbon Steel Spools with Nitrogen Gas 3

[ram0608]

Dear Friends,

In a project, we have PE Lined carbon steel pipes and sucessfully tested for hydrotest at 74.10 Bar (1.5 x MAWP). Now, During commissioning customer is asking to do the pressure test for the line with Nitrogen gas at 34.0 bar?

We would like to know can we test the above PE Lined carbon steel spools with nitrogen gas at 34.0 Bar? If so, what will be the duration of test? Is there will not be any effect of liner integrity? Any body can help in this regard?

Thanks in advance

 

[vpl]

Have you asked your customer any of these questions? Do they have a standard to which they want you to test? Was this test part of the original specification or is it something new?

The test pressure is only 69% of your design pressure and you've already hydrostatically tested it to well over that, so the chances of a catestrophic rupture are small. More likely, the customer is looking for small leak paths which wouldn't be found during the hydro (due to the difference in size between a water molecule and a nitrogen one.)

The length of time is generally fairly short; either the leak will be there or it won't. I've seen mention of using a bubble solution on the outside or a wintergreen infusion with the nitrogen -- something that lets you know that there is a leak.

I wouldn't think that the polyethelene (I presume that is what "PE" means) lining would be damaged by this.

Doing a search (using the grey search button next to the green forum button) might give you additional information.

Patricia Lougheed

******

Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.

 

[EdStainless]

I would resist doing a pressure test with gas at those pressures. The stored energy is frightening.

If they are trying to find a small leak then testing at 150-200 psi will give you just as good of results.

It would be possible to have a tiny leak in the liner and get gas behind it, then when you depressurize quickly you could collapse the liner.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[mbt22]

I suspect that Pat has it with a leak test, but as always the ultimate answer is ask the client.

Incidentally, a 34 bar nitrogen leak test is not particularly frightening if the normal process fluid is a gas. It looks like normal operating pressure for a ~50 bar MAWP system. I would certainly want a good nitrogen or helium leak test at full process pressure before introducing toxics or flammables.

Matt

 

[metengr]

Helium leak check is the way to go for this specific application.

 

[Duwe6]

Or use a Hydrogen mix instead of Helium. 5% Hydrogen / compressed air mix is not flammable, and easily detectabel.

Besides being expensive, helium is a nonreplaceable 'mineral'. When its gone, there will be no more.

 

[r6155]

Hydrotest and leak test should be done before lining the pipe

My opinion only

Regards

r6155

 

[moltenmetal]

If you've hydro'd the piping to 74 barg, and you're still afraid to fill the piping with nitrogen to 34 barg, why are you afraid? That's NORMAL- for piping which is normally carrying gases a hell of a lot more hazardous than nitrogen, 24/7/365- not just for a short-term test!

If your concern is the integrity of the liner rather than that of the pipe, the lining system has to be designed to deal with potential permeation risks because they will be there regardless what you do. And methods far more sensitive than a pneumatic test need to be used to inspect liner integrity PRIOR to this testing, provided that the liner is there for corrosion resistance reasons.