Pressure Testing HDPE Pipe

[gjenkins]

Hi,

We're pressure testing some (approx 400m) HDPE piping with water and our client has given us a spec that we shall increase the pressure in the pipe to 125 PSIG and maintain this for the duration of the test. After one hour we are required to check for leaks.

Now our problem is that we are unable to find any leaks in the fittings etc, but our pressure drops 10 PSIG within 15 minutes of isolating our pump from the piping network. We think we have released all the air from piping. The water has been in the pipe for a few days so temperature gradients should be a problem and we aren't adding any water into the system each time we repressurize. I'm wondering if there is anything else that could be causing this decrease in pressure.

Any thoughts or ideas would lots of help

Thanks,

Gareht

 

[zdas04]

Have you been able to vent the pipe after the water sat for a day or two? I've had real problems with dissolved gases evolving out of the water as it stands without pressure on it. The pressure dropping within 10 minutes of turning the pump off is a pretty good indication that you have gas pockets that get re-absorbed under pressure.

David

 

[joeswoes]

Check the diameter of the pipe, if its expanding from internal presure, then your pressure will drop.

 

[sailoday28]

How long has the piping been pressurized prior to isolating it from the pump?
If the problem is expansion of the piping due to pressure, then I suggest pressuization for a longer time prior to isolation. This should allow the piping to be fully expanded and eliminate that cause for any depressurization.

 

[stanier]

Suggest you obtain a copy AS 2566.1 & 2 Buried Flexible Pipelines Design & Construction from

http://www.standards.org.au.

This has a much better procedure for testing PE than the one you have been given.

What you are witnessing is the creep properties of PE. It doesnt behave like steel or ductile iron.