Control Valve Seat Test Pressure 1

[Sid89]

Does anyone know what is the test pressure for the seat closure test of control valves? Per ANSI FCI-70-2, test pressure should be 51psi (when test fluid is air or nitrogen) which is only a low-pressure test. Per ASME B16.34, the seat testing pressure should be 1.1 x rated pressure of the valve (test fluid is water) but some manufacturers say that this doesn't apply to Control Valves and is only applicable to isolation valves. If what they are saying is correct, then is there any standard that specifies test pressure for high-pressure testing of seats in control valves?

 

[btrueblood]

Don't use a control valve for isolation. Don't use an isolation valve for control. Not rocket science...

That said, you can request that a control valve be tested to the ASME standard to show no damage occurs to the seat, i.e. a ANSI FCI leak test before and after, some manufacturers will do that depending on the seat design. They might even record leak rate at the ASME pressure for information only...

 

[Sid89]

The issue that manufacturers state for not doing seat tests in control valves per ASME B16.34 and API-598 is that high pressure (1.1 x rated pressrue of valve) may crush the seats and they may not be able to seal at low-pressure test parameter per ANSI FCI 70-2. Do they need to change the seat design of their soft seats so it can pass high pressure closure test per ASME B16.34 followed by a low-pressure closure test per FCI 70-2?

 

[bcd]

High pressure closure tests are usually done at 1.1 times the valve seat or closure differential pressure rating, which can be less than the rating of the valve body. Refer to paragraph 4.3.3 in ASME B16.34. When the valve has a seat rating less than the body, it is marked on the identification plate.

 

[btrueblood]

"Do they need to change the seat design of their soft seats so it can pass high pressure closure test per ASME B16.34 followed by a low-pressure closure test per FCI 70-2"

Pretty obvious the answer to that..."should we change the design of the seat if it wasn't designed to that pressure?"

Design change of the seat may affect its ability to control at low flow rates, have repeatable/non-hysterical Cv vs. opening characteristic, etc. Again, use an isolation valve upstream of the control valve if leak tight shutoff is required, problem solved.