PSV test fluids.......

[aminersson]

Can anyone please advise how to determine what test fluid should be used to test the set pressure on a PSV. Any help or reference to standards would be appreciated.

 

[JAlton]

ASME Sec. VIII, Div. 1, Para. UG-136(d)(4)
requires New Gas or Vapor Service valves to be tested on Air, Liquid Service Valves to be tested on Water and Steam Service to be tested on Steam, unless the Steam Valve is too large or too high Set Pressure. Then they may be tested with Air provided a compensation factor is applied.

NBIC, Para. RE-2010 requires the same as ASME Sec. VIII, Div. 1, for repaired Valves, with the exception of Steam service valves tested on Air. Only owner/users are granted permission to use steam to air correlation factors under the National Board "VR" Program.

J. Alton Cox

http://www.delucatest.com

 

[JAlton]

NOTE: For clarification, the capacity units on the PSV Nameplate may be useful in determining the appropriate Test Fluid. Lbs/hr or PPH indicate Steam Service and require testing on Steam. SCFM indicates Air/Gas Service and requires testing on Air. GPM indicates Liquid service and requires testing on Water.

In some cases, the capacity may indicate a fluid other than the actual service. If this is the case you should verify that the PSV is suitable for the application and then test it according to the actual service condition, steam, air or liquid. If the PSV is not suitable for the application, it should be replaced or converted to the correct trim prior to testing. Air service valves in Lquid service may not attain full lift at 10% overpressure and therefore may not provide the required overpressure protection. Liquid PSVs in Air or Steam service may not have the proper internals to attain full lift on compressible fluids.

J. Alton Cox

http://www.delucatest.com

 

[zdas04]

Another important point is that the test record needs to capture both the lift pressure and the reset pressure. For PSV's intended for compressible applications doing a liquid test (not recommended by JAlton above for many good reasons, they're still done sometimes) makes it very difficult to see the reset point since it happens so quickly.

David

 

[JAlton]

Regarding Testing, for compressible fluids you really need sufficient volume to get a representative pop and reseat. Low volume test equipment (less then 3.0 cu ft) typically will not provide reliable lift and blowdown data. For incompressible (liquid) fluids, a J-Tube or Dip Tube design vessel is desirable. Hydrostatic pump type test equipment is very difficult to determine set pressure using NB-18 criteria.

J. Alton Cox

http://www.delucatest.com