Check valves in PSV paths

[AndreaMDan]

I have somewhat of a repeat question that was asked and answered in ~2007 and I was interested in getting a fresh/updated perspective if there is one. What, if any, code requirements are there regarding installation of check valves in relief valve pathways? It is clear from reviewing ASME BPVC that an intervening stop valve must comply with certain requirements and that any fittings in the upstream piping system must not reduce relief capacity below that required or introduce valve stability issues. However, while I believe use of check valves in relief paths introduces an unacceptable process safety risk in vast majority of cases, I can't find anything in code or standard that strictly prohibits this.

Does anyone have any fresh perspectives on this topic?
Thanks in advance.

 

[The Obturator]

You need to review the latest requirements of Stop Valves when used with Pressure Relief Systems, in ASME XIII (2023) Non-Mandatory Appendix B.

A Check Valve, being a non-return valve, cannot be a 'Stop Valve' in this sense.

What is the reason for a check valve and why not use a traditional stop valve such as a gate valve etc.?

 

[georgeverghese]

Obviously, the pressure drop induced by the check valve should be included in the obligatory PSV inlet path pressure drop calcs.

My old Co guidelines tell me an intervening check valve in the relief path to the PSV may be accepted on the condition that the pressure seen at the protected equipment, for the case when the check valve is completely blocked, does not exceed 1.5x the setpoint of the PSV.

All check valves in relief paths should be capable of staying full open during a fire - add fire proof insulation at check valve if required.

 

[goutam_freelance]

I have a feeling that safety requirements in ASME are being diluted similar to what's happening in Boeing. This may be due to large corporate interests seeping into code requirements.

 

[udyman]

API 520 Pt II has the following guidance on check valves.

Check valves shall not be installed in PRD inlet or outlet lines since these devices are normally closed and the check valve can become stuck in the closed position or fail in a manner causing an obstruction in the PRD path.

I personally would never design a system with a check valve between a PSV and the protected equipment. If I came across one when revalidating a relief system, I would recommend the client remove it or move the PSV upstream of the check valve.