One thing I have never found is a good book on power hydraulics with a section on testing including acceptable leakage rate determination. For piping I consider 3 tests when deciding what tests to apply:
2)Low pressure hydro test.Fill the system with operating liquid at around 10% of design pressure (taking care to minimise trapped air) and then go looking for leaks. Poorly fitting seals nearly always leak more at a low pressure than a high one. I normally isolate the system at pressure for 5 or so minutes and watch the gauge just in case I have missed a leaker. The low pressure test is just an add-on to the high pressure test.
3) Full pressure hydro test. This test is the official test for the record. It’s the one that officials are permitted to witness if they choose. Test duration is always an issue. I like to keep the pressure on as long as possible. Most of the "failures" I have had have been due to weeping from valves; normally the test or vent valves. However there is always the possibility that a gasket or seal might blow out or something might crack.
Cheers
Steve
-----Original Message-----
From: PipingDesign@yahoogroups.com [mailto:PipingDesign@yahoogroups.com]
On Behalf Of Jack Osborn
Sent: Friday, March 24, 2006 8:21 AM
To: PipingDesign@yahoogroups.com
Subject: Re: [PipingDesign] Hydrotest vs pneumatic test (Things That Go
Boom continue)
Thank you for your comments Elie....
I had a similar issue with hydraulic piping (1750 working psi). The contractor wants to use air or nitrogen to check for leaks on 3/4" hydraulic line. I am reluctant to allow it, but would like to see some standard testing procedures for this type of hydraulic system.....would you know of anything that might spell out this out? (Maybe Steve or ??)
thanks!
Jack
Many times when I specified hydrotesting at 110% up to 150% of MAOP (depending on applicable code) and the client requested that we modify the test from hydyo to pneumatic test for economical reasons. I typically refer the client to the applicable code section on pneumatic testing and decline to issue an official procedure.
The reasoning behind this is that the test is to proof that the pipe is strong enough to sustain the pressure and rupture is possibility, the reason we are doing the test.
For water under 100 psi the water expand very little after a failure. For gas the volume will expand by (100+14.7)/14.7 = 7.8 time.
Pneumatic test is OK on lines 3/4"NPS or smaller that are intended for instrument gas line.
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