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1434 views
19:32 Jan-22-2009
Omer Javed
Effect of water in Helium leak testing

We already have an image that presence of water is not good during Helium leak testing specially using Sniffer method.

We want to test our vertical type high pressure exchanger ( installed in area) for any leaks in tube-to-tube sheet seal welds using helium leak test( sniffer method based on mass spectrometry). Now the problem during testing bottom tube sheet of this vertical exchanger, we are unable to remove water from annular space of tube sheet (because the drain nozzle is an inch above bottom tube sheet).

Now the question is, "by pressuring the shell with helium, will this helium be able to diffuse through this layer of water and come out of leaks of seal welds and in turn be detected"

 
01:11 Jan-23-2009

Dent McIntyre

Consultant, NDE Manager NDELevel III/3
NDT Consultant,
Canada,
Joined Nov 1998
247
Re: Effect of water in Helium leak testing In Reply to Omer Javed at 19:32 Jan-22-2009 (Opening).

Been there done that. You are correct.
Water will effectively plug any leak preventing helium from passing. Pressurizing with helium/air will just drive it in further.

What you need to do is one of 2 options.
1) bake the lower tubesheet to dry it out or 2) draw a vacuum on the shell side to effectively remove the water.

 
01:31 Jan-24-2009

faran

Engineering
FFC Pakistan,
Pakistan,
Joined May 2005
17
Re: Effect of water in Helium leak testing In Reply to Dent McIntyre at 01:11 Jan-23-2009 .

I have a question, when Helium can diffuse thru Nuprene (rubber) which happens to be a solid why cant it pass/ diffuse thru water molecules.

 
07:39 Feb-12-2009

Faran

Engineering
FFC Pakistan,
Pakistan,
Joined May 2005
17
Re: Effect of water in Helium leak testing In Reply to faran at 01:31 Jan-24-2009 .

We performed an experiment and concluded that Helium does not pass thru water, however Helium molecules do penetrate in water at pressure. These molecules are given off when pressure is removed. Bottom line that successful Helium leak test using sniffer method cannot be performed when there is water present/ trapped in the leaking path.

 
12:22 Feb-12-2009

Dent

Consultant, NDE Manager NDELevel III/3
NDT Consultant,
Canada,
Joined Nov 1998
247
Re: Effect of water in Helium leak testing In Reply to Faran at 07:39 Feb-12-2009 .

Can we have some details on your experiment?

 
03:25 Jul-23-2011
Joseph Azzara
Re: Re: Effect of water in Helium leak testing In Reply to Dent at 12:22 Feb-12-2009 .

What are your thought on a trace gas using 95% nitrogen and 5% hydrogen coupled with a hydrogen detector?

 


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