Butterfly at outlet of PSV 4

[Vladimir99]

We have an installation with a butterfly valve (isolating valve) at the outlet of a psv. We usually put gate valve with CSO. Is the used of that kind of valve allowed with APi *(Is this consider a block valve). My application is for light naphta.

Thanks,

 

[dcasto]

Risk Management. The butterfly valve can be a good valve if it is not operated a lot. I'd certainly look at the size and location and make a final decision. Metal seats give a more positive seat, but wear if used a lot. The disk should not add enough pressure drop to the relief, but it doesn't hurt to make sure the header model takes it into account.

 

[Vladimir99]

Thanks dcasto,

my application is a 4'', 150# butterfly valve with TFE seat.

Will the teflon seat wear as the metal seat ?

Regards,

 

[EGT01]

Vladimir99,

Whether you consider a butterfly valve adequate enough for isolation is one issue.

What may be a more important concern is whether you can ensure that the valve disk does not somehow become disconnected from the valve operator and block the flow.

API RP-520 Part II specifically notes...
"When gate valves are used, they should be installed with stems oriented horizontally or, if this is not feasible, the stem could be oriented downward to a maximum of 45' from the horizontal to keep the gate from falling off and blocking the flow."

It would seem you could have a similar concern with a butterfly valve but I don't think you could position the valve to address the concern the way you could with a gate valve.

 

[lizking]

ASME Section VIII, Appendix M, M-5.6 indicates that full area stop valves may be used upstream or downstream of a PRD with provisions......(a through e). I don't think a butterfly valve is considered "full area".