Oil Line Pressure Test - Air or Oil? 1

[ewooden]

I have a few lube oil lines being replaced and the spec calls for an air pressure test which I know to be dangerous. Is this standard for oil pipes or would it be better to run the test with the oil?

I don't think we want to use water, as we'd never get it all out, and if we used oil it could catch fire if we require re-welding of a joint. I'm stumped. What is the industry standard?

 

[jtseng123]

air test in a bunker. Also check the potential stored energy if you know the formula. Google and you may find if exceeding some value, the risk is high.

 

[ewooden]

Bunker wouldn't be an option, these are service pipes between equipment.

 

[zdas04]

You didn't mention line size or length so it is hard to get a feel for the magnitude of risk.

I live in very hilly country (the Rocky Mountains) so in a risk matrix I am usually more concerned with hydrostatic gradient than I am with pneumatic tests explosively decompressing and I do pneumatic tests with air all the time. The formula mentioned above comes up a lot in this discussion and it is primarily nonsense. It came from a NASA theoretical evaluation (no actual tests) where they assumed that all of the stored energy in the pipe would participate in the explosion. In real life most of the energy in an explosive decompression is expended in simple pipe flow to the new opening. The equation results in a MegaTonne level explosion from a long, big-inch pipeline failure. Poppycock. A failed pneumatic test is dramatic, but not on a par with a nuclear bomb going off.

Tests with air, water, glycol, and lube oil can all be done safely, the key is understanding the risks associated with each and writing the test procedure in a way that minimizes the risk of the media you've chosen. You need to remember that VERY FEW tests fail, so the most likely outcome will be a successful test and then you have to decide what to do with the test media and prepare the system for service. For lube oil lines I prefer to use the same oil that will be in the lines once they are in service and just leave the oil after the test. That assumes that there is adequate filtration for any mill slag or disturbed sludge that disposing of the test media would normally get rid of.

David Simpson, PE
MuleShoe Engineering

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