Overpressure in Pressure Testing

[Bluecat46]

Hope some one can help.

I have been looking at the NORSOK Standard on Piping fabrication,install, flushing and testing (L-004)and section 8.3 Test Media makes the statement below.

"For pneumatic testing, the test media shall be oil free, dry air or any inert gas. The use of air for testing shall
be limited to a maximum pressure of 0,7 MPa overpressure. Above this pressure nitrogen shall be used. The
extent of pneumatic testing shall be approved."

Whats is meant by overpressure in this statement?

 

[zdas04]

It could mean almost anything, but the only answer that makes sense to me in this context is "pressure above atmospheric pressure", or "maximum pressure of 0,7 MPag". You could take it to mean pressure above MAWP, but a constant value for any MAWP doesn't make any sense. I'm betting it came from some US nonsense that limited tests using air to 100 psig.

"Overpressure" is one of those terms that is almost always ambiguous and Standards-writers should be flogged for using it.

David Simpson, PE
MuleShoe Engineering

Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat

 

[LittleInch]

As this is NORSOK, I would take a guess at it meaning over and above the static external pressure in case the item you're testing is sitting on the seabed. Either that or a bad translation...

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[zdas04]

Do you think? If I'm in 100 m of water, the static external pressure is 0.981 MPaa so the air introduced could be up to 1.7 MPag and when I've seen limits on air tests I haven't seen them go that high. Could just be my limited experience offshore.

David Simpson, PE
MuleShoe Engineering

Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat

 

[BigInch]

Hydrostatic pressure at 100m below sealevel x 3.28083 = 328.08 ft, 328.08 x 64pcf(in seawater) /144in2/ft2 = 145.8 psi
+ Atmospheric pressure 14.5 psi =
Total Exterior pressure = 160.3 psia
Total exterior pressure = 1.10 MPaa

Not important how much air needs to be introduced, just the final differential pressure. So that looks like pneumatic tests are limited to 100 psiG maximum test pressure above or below the waterline.

I hate Windowz 8!!!!