Tightness test

[Ast83]

First of all thanks for your attention. The client is requiring me a tightness test (which i understand is a type of pneumatic test) after hydraulic test of several pressure vessels. The design pressure for this equipment is 22 kg/cm2g and he says that this has to be performed at a pressure >= of this design pressure. Do you have experience with this type of tests and specially at this pressures? Do you know if this is acceptable due to safety questions and what measures we have to take?

Thanks in advance for your respond.

 

[doct9960]

Ast83,

So your client wants "gas leak testing at a minimum pressure of 22 kg/cm2g" after hydrostatic test of the vessel? Is this additional testing part of your purchase order or contract with the client? If not, don't do it.

 

[metengr]

The client is requiring me a tightness test (which i understand is a type of pneumatic test) after hydraulic test of several pressure vessels.

Why? I see no purpose for a tightness test requirement if a successful hydraulic test had been performed. Also, there is indeed a safety issue for a pneumatic test at 22kg/cm².

 

[Ast83]

Yes, this test is specified at the client specifications. Recently they have also sent us an email clarifying the specifications for this test. Follow you can see them:
1. Tightness test should be performed after hydrostatic test approval. Tight test pressure should be design pressure at least.
2. The test temperature should not below 5 ? for the of vessel which made of carbon steel or low alloy steel.
3. The gas of test should be clean, dry air, nitrogen gas or other inert gas.
4. To inspect all weld seam and connection by using soap bubble. No leakage can only be accepted. If leakage occur, vendor should perform
this test again after patch up the leakage.

Also they are talking about perform this test with the equipment painted. But i am still more concerned about the pressure of the test (22 kg/cm2g) than the issue of when to perform this test...

 

[OSIRIS7]

A pneumatic test is allways a risk. However, when a hydrostatic test has been performed at a pressure that is larger than required for the pneumatic test, it can be assumed relatively safe. But beware of local and/or national rules with regard to safety precautions.

In my opinion this thightness test is more to test for leakage at flanges as it is for welds.

Also if the vessel has been hydro tested, water still might block opportunities, which, because of the residing water, might not be exposed during the thightness test.

Have you considered a helium test in advance of the hydro test?

 

[Ast83]

Thanks for your opinion.Finally we will perform this test after the hydraulic test and once the equipment is completly dried. We will use compressed dry air for the test. The option of the helium test is not economical for us and since it will be ok for our client if the hydrostatic and tightness tests are passed we won´t perform any additional test.
Thanks all for your support.