Regarding hydro test pressure and temperature relation.

[purode333]

Dear sir/all,

We have 2.5 KM of C.S. pipe line, and we have start the hydro test at 5pm with 18kg/cm2 and as per holding time of two hours , it is completed at 7pm , without any leakage or seepage.

But after completion of 2 hrs., pressure decrease by 1hrs. and it found 17kg/cm2.
We stated that due to decrease in temperatures, pressure also decrease. but client not ready to accept.

Pls help.

Design pressure is 12kg/cm2 and hydro test pressure is 18 kg/cm2.


Regards
Prasad

 

[JohnGP]

purode333, I could understand the client not willing to accept the assertion that pressure decrease was only due to temperature decrease without any substantiation. As a minimum I would expect that you would need to have a record of temperatures at start and finish, with calculation to demonstrate the effect of the temperature change on pressure. If available, Shell DEP 31.40.40.38-Gen has a formula to check whether pressure drop is due to temperature change, but a search should uncover other references.
Cheers,
John

 

[purode333]

Sir,

Thanks for reply.

I want to know, is any standardized chart, regarding this pressure and temperature difference.

Or any thumb rule to consider this. As this is very common query, we have found in hydro test at any location.

Thanks again for response.

Regards
Prasad

 

[LittleInch]

Not sure why this is in boiler and pressure vessel forum instead of Pipelines, but totally agree with JohnGP.

A 2hr hold period is unusual - what code are you working to?

There is a good calculation also in BS PD 8010 pt 1 to calculate this effect.

Temperature decrease could be responsible, but you need to have measured inlet temp, ground temp and demonstrate it.

Also how long did you leave the water to equalize with the ground temperature - normally you need a few hours (>4), but depends on line size - how big is your pipe.

Of course you could have a leak.....

Or you could just pump it back up to 18 kg/cm2 and start your hold period again....


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

 

[r6155]

See API RP 1110.

Regards
r6155