Pneumatic test; what if we use 7bar compressurized atmostphere combined with 5bar nitogen

[duong hai]

Hello guys, please help me this question. Our contractor carrying out pneumatic test for a pipeline, Pressure test for the package is 12bar, they want to use 7bar of compressurized atmosphere and 5bar of nitrogen. The procedure of pneumatic test require all package with test pressure above 10bar must use nitrogen as medium. Thank you guys so much!

 

[TugboatEng]

From my experience, high pressure nitrogen from cylinders is used for testing in the field because the facility's air compressors cannot provide the air pressure required to perform the test. Without specifics on application, I don't see issue pre-charging the system to the maximum pressure the air system is able to provide and then continuing to the test pressure using nitrogen.

If the spec truly requires nitrogen above 10 bar for contamination or explosion reasons, you should probably stick with nitrogen only. If the 10bar limit is due to compressor output, the consult the engineering department about rewording the requirement.

 

[LittleInch]

Must use nitrogen.

Why?

Seems a bit odd but guess the contractor wants to save some money?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[pierreick]

Hi,
Better to use water to perform this kind of test ( hand pump) ,safer .
My 2 cents
Pierre

 

[TugboatEng]

Water is not always best. My example would be a diesel engine cylinder. We have ~200 psi air available when we need to simulate 1000+ to tes for leaks. This isn't a test to failure like a typical hydro test. We already know the system will handle the pressure, we're looking for the leaks.

In a very large system such as a pipeline, it would make sense to charge it as much as possible with cheaply available gas. Nitrogen isn't going to show a leak any more readily than 70% nitrogen atmosphere gas. Nitrogen, however, is the least expensive high pressure transportable gas.

 

[MortenA]

@tugboat, pierreick is right wrt to safety though. I dont think a hydro test i "typically to failure", actually i never heard of it for piping or pipeline. You have a predefined test pressure (e.g. 1.46xMAWP depending on code) and then you test for a specific time.

And testing with a gaseous medium can be difficult due to temperature variations causing pressure variations.

Best regards, Morten

--- Best regards, Morten Andersen