Pressure testing pipework...

[Masood]

Just idly thinking about a job I did a while ago, which was the last time I pressure tested new installation pipework. I had 3 bar mains pressure (give or take), so pumped up to 4.5 bar and left for an hour. Zero pressure drop. But when I commissioned the system, there was a small drip from a soldered elbow. Surely this should have caused a pressure drop on the test? Has anybody else had similar experiences with pressure testing? Just wondering what might cause this...

 

[Keefy]

Theoretically I'd say the sudden drop from 4.5 bar pressure has caused it to pop, expanded then suddenly contracted? Like I say, just a theory.

 

[Toxic Ted]

Air is compressable and liquid is not. If you want to pressure test pipework then either buy yourself a hydraulic type where you pump the pipework full of water or fill pipework with water and then air pressure test from the highest point. This way the air available to compress is minimal so you will get a visible drop on the guage and on the pipework.

 

[SimonG]

Cold pressure test vs hot commissioning?

 

[Destroyer2813]

Did it go under heat, you probably know how things are fine when cold then pop when hot

 

[AWheating]

could be movement of water.

 

[Masood]

Theoretically I'd say the sudden drop from 4.5 bar pressure has caused it to pop, expanded then suddenly contracted? Like I say, just a theory.

Interesting, and totally feasible IMO...

Air is compressable and liquid is not. If you want to pressure test pipework then either buy yourself a hydraulic type where you pump the pipework full of water

Should have said, I have a hydraulic type - one of these Rothenberger RP30 Pressure Testing Pump | NoLinkingToThis

Did it go under heat, you probably know how things are fine when cold then pop when hot

No, balanced cold from an unvented cylinder's inlet control group...

could be movement of water.

Not sure what you mean by that, LOL! There was water moving within the pipe, of course, but under lower pressure than during the test...l

 

[AWheating]

what i ment was once in use the water moving through the fitting could have removed the flux holding the seal? or effects of water hammer maybe?

 

[Masood]

what i ment was once in use the water moving through the fitting could have removed the flux holding the seal? or effects of water hammer maybe?

Ah right, got it! Also possible - anyway, no getting away from it, it was a weak joint, so I'd rather it went while I was there!