DIP Leakage Test - Pressure Increasing

[hocha]

I am currently witnessing a leakage test on an 8" DIP. The test requires the contractor to maintain a constant pressure in the line (by adding more water if leakage occurs), and then to measure the total volume of water added over the course of the test.

The first go-a-round, over the course of 4 hours, the pressure in the pipeline increased from 150 PSI to 200 PSI. I pointed out that the pipe was not buried and that the temperature increase was most likely causing the pressure increase. The contractor buried part of the line (but not the entire line, as they have work that requires portions of this trench to remain open) and began the test again today. Less than an hour in, the pressure is still rising (although not as dramatically as before). Without making the contractor fill in the entire trench, is there a way to perform this test properly?

 

[bimr]

The best course of action is to use the pressure test procedures in the Standard Specifications.

You probably have air in the pipes. Have the pipe flushed adequately prior to the test.

 

[rconner]

I agree with bimr. Of course (as you are probably aware) AWWA standard C600 for installation and testing of ductile iron mains, I suspect now like many other testing specifications, suggests that air be removed/vented before test, and also that DI mains are most generally tested with the backfill in place (as they will service for the Owner).

About only other thing I can think of (and this would admittedly/probably be a very rare case) is if by any chance your happen to be testing against a test boundary consisting of a closed valve with higher pressure on the "other" side, and you have a leak bleeding by that side onto your new test section!

[All that being said, I wouldn't be surprised if you have a good line with still increasing pressure after 4 hours!]

 

[hocha]

The air in the line was bled prior to starting the first test. I witnessed that procedure. The line is also completely isolated. I had the contractor put plywood over the exposed line to give it a bit of shade. The pressure dropped back to 150 PSI and remained there for the duration of the test.

 

[bimr]

Air trapped in pipeline may cause the pressure readings to be unusual. Pipes are often laid with pockets (dips, sags, highpoints) that trap air. You may also have elevations differences that make if difficult to remove air. To adequately remove air in a 8-Inch pipeline, you probably need a flow of approximately 600 gpm to give you a velocity of 3-4 ft/sec to push the air out.

One would suspect that a slug of water pushed down the pipe to get that kind of pressure drop. I don't think it was the sun.