control valves and piping hydrotest 1

[elylrc]

In the past we have hydrotested systems prior to installing control valves by installing a short spool in lieu of the valve. I have a contractor who is insisting that this is unnecessary. The system is ANSI 600#, Class Location 3, per B31.8 2007. The design pressure is 1440 (not 1480)and the test prtessure is 2016. The valve is by Mokveld.

Any advice will be appreciated.

 

[davefitz]

elylrc,

Methinks you may be undertaking some wishful thinking.

A quick review of ansi b16.34 , par 2.5.3 "Pressure test limitations", 2.5.3.1 "valve in the closed position", and 2.5.3.2 "valve in the open position" makes it explicit, that any pressure test that occurs at a pressure above its 38 C ( 100 F) pressure rating or differential pressure rating is soley at the risk of the user. So that is , zero overpressure is permitted , based on 100 F rating. So, it may be an issue for valves that noomrally operate at 100 F.

It is true that B31 allows 10% overpressure during transients, but if a valve were to fail durig hydrotest, and you were to try to get a free replacement from the vendor, it is likely that he will take refuge in the B16.34 statements.

 

[elylrc]

Pipeline valves are per API 6D per B31.8. I'm sure you may be correct in other applications.