Hydrotesting of Process Piping

"I have to carry out hydrotesting of process piping follow ASME B31.3. When I hold at test pressure, it is no leak but the pressure decreases about 10%."

A 10 % drop in pressure would indicate to me that there is a leak somewhere and steps need to be taken to find it. What is the volume of the pipe being pressure tested? How long does it take for the pressure to drop 10 %.??

Thank you Stirling Stan, It was done but I would like to know the basic of acceptance. How many percentage drop in pressure is allowable and where it was stated in the code? The pipes was 2" with length of about 300 meters connected each other by flanges. Test pressure was 300bar, It was hold in 4 hours and temperature changed from 36 deg. C to 28 deg. C

You need to apply temperature correction factor then check ie you need to calculate for 8deg droop in temperature will make large diffrence in pressure.Probably you are noticing 10% pressure diffrence with out noticing any leak due to temperature droop

The values for temperature, roughly, indicate a pressure loss of 2,7%. (Po/To = P1/T1). A little too far from 10%, there is some leakage a small one. Be sure about that. Have you used leak-tek all around? ( leak tek in 300 m of pipes... )

After all, it's up to you to determine if your process accepts the leakage.

It's strange to hear about that, normally, statice pressure tests doesn't take so long.

Rejectable media leakage. 10% press loss with stable temp over 24 hour period is rejectable amount of leakage.

Hello,

I dont know much about your application, but sharing some facts - No system is leak proof. We are checking some parts for leakage in which we are required to conduct dry test for leakage thr system, using pressurised air. We have established as a thumb rule that - if the parts are tested for 6bar pressure air and found ok, then those parts can withstand about 10bar pressure of oil. Similarly, may be you can establish some relation between water and actual media / fluid that would be flowing thr pipes after installation. This probably will define level acceptance of leakage during hydrotesting for your desired application. Secondly, as posted by many of them in this thread, Temperature is major factor and if you conduct test at maintained ambient conditions, you will be in a position to judge your test process in much better way. Hope you got some hints here.

We inspect and service fire extinguishers.

Every 12 years fire extinguishers have to be dumped and hydrotested. All water supply lines have to filled with water (no air within the system), we hold the pressure for 30 seconds at approx. 600 psi. Fire hoses are held at 250 psi for 3 minutes.

If they leak, we check all fittings ensuring connection and no air leakage using liquid soap or other.

I hope this helps.

Remember that any gas entrained in the process piping is compressible and will manifest as a drop in pressure during hydrostatic testing.

300 meters of pipe! Pepper is right. Most likely air. Pump it up again until you stop seeing pressure drops and keep checking the flanges. And you shouldn't have to wait four hours. Industry practice is anywhere from 15 minutes to an hour. That will also limit the any temperature changes from affecting the test.

Pressure tests can be frustrating. Let us know how it goes.