Isolation valves allowed upstream of relief valves?
Isolation valves allowed upstream of relief valves?
(OP)
ASME B&BVC, Section VIII, Appendix M (I think) allows full-area stop valves to be placed upstream of pressure vessel relief valves, provided that certain provisions are met, such as keeping the stop valve locked open and keeping a person at the valve at all times whenever it is shut. While these provisions make sense, I have to admit that the idea putting a stop valve in front of a relief valve still makes me uneasy. Are there any "hidden catches" to this allowance that I'm not aware of? I'm no expert on Section VIII.
Note: Our engineering group has been asked to look at possible solutions for fixing and maintaining a relief valve with a long history of repair problems. That is, the valve will occasionally lift and then fail to completely isolate when it reseats. Adding an isolation valve would allow the relief valve to be worked on without taking the associated heat exchanger out of service. Obviously, there are other issues at work here, such as why the relief valve occasionally lifts and why it does not properly reseat. However, I'm exploring all options, and adding an isolation valve is one that has been put forward.
Thanks.
Note: Our engineering group has been asked to look at possible solutions for fixing and maintaining a relief valve with a long history of repair problems. That is, the valve will occasionally lift and then fail to completely isolate when it reseats. Adding an isolation valve would allow the relief valve to be worked on without taking the associated heat exchanger out of service. Obviously, there are other issues at work here, such as why the relief valve occasionally lifts and why it does not properly reseat. However, I'm exploring all options, and adding an isolation valve is one that has been put forward.
Thanks.





RE: Isolation valves allowed upstream of relief valves?
RE: Isolation valves allowed upstream of relief valves?
Good luck!
jproj
RE: Isolation valves allowed upstream of relief valves?
RE: Isolation valves allowed upstream of relief valves?
RE: Isolation valves allowed upstream of relief valves?
RE: Isolation valves allowed upstream of relief valves?
At our plant, we have already *sort of* done this before. That is, we have placed stop valves in series with thermal relief valves on other heat exchangers. However, in those previous cases, we took credit, procedurally, for other relief paths whenever the thermal isolation valve was shut. In this most recent instance, we don't necessarily have that option.
I'm going to talk to our inpector this afternoon. I'll find out then what his interpretations and recommendations are.
What, exactly, is a "car seal"?
RE: Isolation valves allowed upstream of relief valves?
I have to admit, though, I re-read Appendix M after my last post, and Davefitz may have a point. I always considered car seals positive control, but appendix M refers to car seals specifically, so the non-mandatory aspect of the code may take precedence here.
RE: Isolation valves allowed upstream of relief valves?
I don't think we have any PSV's at the plant I work in which do not have a block valve (boilers are an exception to this). They are CSO'd and shown as such on the P&ID's. We frequently have spare PSV capacity which allows for servicing them on the run by taking them out of service one at a time. For example, we have one large vessel which needs four PSV's and has five installed.
jt
RE: Isolation valves allowed upstream of relief valves?
-pmover
RE: Isolation valves allowed upstream of relief valves?
RE: Isolation valves allowed upstream of relief valves?
as your UG 135 statement reads, closing the maximum amount of stop valves POSSIBLE could mean closing of all car sealed valves, since that is a possible configuration, but in the case of a 3 way valve, it is not possible to reduce the relief capacity by any possible valve movement.
I think that the non mandatory appendix can be used with inspector's approval. In the design state, the EPC contractor would need a letter from the insurance carrier that they approve of the arrangement prior to final dwg approval by the site prof eng. ( I also worked for an EPC for 3+ yrs, and the code compliance was not uniformly followed by all lead engineers- spotty at best. )
RE: Isolation valves allowed upstream of relief valves?
We have a lot of overhead/procedure/auditing invested in CSO-ing but on the plus side it allows SV's to be overhauled when required - rather than in bulk at shutdowns.
By the way, the isolation valves have a host of requirements - including full porting, and in the case of gate valves, ideally installed upside down... just incase the gate drops.