Nitrogen

Thank You for your Comments

But

In that Pipe already Hydro test Complete( Above 1.5*800psi ) , there have no leaks in flange and welding joint also. but the pressure drooped day by day .so only i asking is there any possible way to calculate the pressure drooping .

temperature also we considered

but

Long time we stored N2 in pipe means any drooping coming or not ,because day by day appx 10-15psi drooped

one more doubt

if N2 is stored long time means what happened (stored in pipe with pressure)

Hydro testing is a very good and safe method of leak testing. However, it is not a perfect test for gas leaks. As you've now discovered. Calculating the pressure drop rate is very simple and straight forward. ΔP/Δt

Once one knows the pressure drop rate and therefore the flow rate, one might be able to back calculate the leak area using the Venturi effect equations but that doesn't seem helpful to me. Knowing that the leak area is N square microns in area will not help finding this leak.

Depending on where this pipe resides, finding the root cause of this leak may not be easy. If this pipe is fully exposed then a soapy water exterior leak checking wash will produce tell tale bubbles at the leak site. If instead this pipe is buried in the ground then one might consider a radio-isotope or chemical sniffer injection into the N₂ and using the appropriate sensor to find out where one needs to excavate. One might even find that an erroneous, porous pipe material (rusty cast iron) was used.

thank you very much for your valuable comments

Thank you

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