Check Valve In Relief Valve Discharge Line
Check Valve In Relief Valve Discharge Line
(OP)
A survey of an existing steam relief valve installation shows the 4" valve outlet connected to a 4" discharge line that connected to an 8" vent header to the roof. (There are other lines tied into the 8" vent header.) There is a 4" check valve in the 4" relief discharge line where it connects to the 8" vent header. Aside from the backpressure questions, is a check valve in a relief discharge line allowed? I would have thought that there could be a situation where the check valve fails to open.





RE: Check Valve In Relief Valve Discharge Line
RE: Check Valve In Relief Valve Discharge Line
RE: Check Valve In Relief Valve Discharge Line
David
RE: Check Valve In Relief Valve Discharge Line
RE: Check Valve In Relief Valve Discharge Line
Aside from the code requirements prohibiting check valves please know that check valves have been known to fail in the closed position. Imagine that happening in a relieving situation.
RE: Check Valve In Relief Valve Discharge Line
RE: Check Valve In Relief Valve Discharge Line
David
RE: Check Valve In Relief Valve Discharge Line
RE: Check Valve In Relief Valve Discharge Line
I'm with David on this - I can think of no situation where a non-return valve would be acceptable in a relief header.
Matt
RE: Check Valve In Relief Valve Discharge Line
The only time I've used a check valve in a flare system is on gas engine starter exhaust that ties into the flare header. You're correct - no other use of check valves would be appropriate in a code based relief system.
RE: Check Valve In Relief Valve Discharge Line
That scenario is credible and doesn't require unrelated events to happen concurrently.
Flare-header analysis is very complex and needs to consider a really wide range of possible scenarios. When a new stream is tied into it, the entire analysis is required again. In a plant where management has decided to bring in a fundamentally different stream, one of the costs of bringing that stream into the plant is an analysis of the flare header and the associated costs of modification. If you have a sweet-gas plant and the decision is made to add an amine system to handle sour gas, you need to build a new flare header as part of the cost of conversion.
David
RE: Check Valve In Relief Valve Discharge Line
RE: Check Valve In Relief Valve Discharge Line
End of the day, its cheaper to rate everything for Sour service, or run two Flare headers.