Isolation valve(Block Valve) installation for Rupture Disk & PSV 3

[Nasim12345]

Dears

I need your advice for below query.
In our plant Drum is protected by One PSV & One Rupture Disk. Can we install isolation valve before the Rupture Disk? It is allowed by code? We have another Drum protected by multiple PSVs & RDs, isolation valves are there, and there is no issue. We received a request to install isolation valve for single PSV & RD, which is installed to protect the Drum.

 

[LittleInch]

Not usually no.

A RD is there to protect against very large volume events which the relief valve can't handle.

The PSV is there to protect against small volume events without destroying the RD.

If you've only got one then by installing a valve you then have no protection from one or the other event.

Multiple ones allow one to be closed whilst maintaining protection as the other can't be closed at the same time (either by procedure or interlocks).

I would refuse the request.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[The Obturator]

ASME VIII (2019) Non Mandatory Appendix M-5 - States that a 'Stop Valve' in the relief path is not allowed unless certain conditions are met as detailed in this appendix,

ASME I (2019) PG-71.3 Does not allow any 'valve of any description' between vessel and safety valve.

Per ISO-4126, only the term Safety Valve is used regardless of applicatin.

 

[Nasim12345]

Thanks for your feedback

 

[don1980]

Installing isolation valves under relief devices is a practical necessity in most cases. And it's an acceptable practice (except for ASME Sec I boiler applications) as long as you implement high-integrity administrative controls (e.g. seals or locking devices on valves) for managing those isolation valves.

The inability to isolate relief devices creates a high plant-reliability risk. Also, the inability to isolate a relief device creates potential safety risks when relief devices are pulled (insufficient vessel clearing, or accidents that can occur during that clearing process).

Having isolation devices under relief devices is a safety risk, but it's one that can be safely managed. And when you consider all the risks (safety and plant operability) associated with not having isolation devices, this is a pretty easy decision for large processing facilities.

 

[pierreick]

Hi,
Attached document from manufacturer about installation .
Pierre

 

[georgeverghese]

Depends on the service of the drum, whether this PSV is for firecase or operational emergencies, its criticality in operations, and plant operating culture for this plant. Sometimes, you have block valves both up and downstream, some times only downstream, sometimes only upstream and sometimes none at all. You havent told us enough. Also read up the sparing and isolation philosophy design report for this plant, if there is one.

 

[biff44]

a valve in front of a rupture disk?

she go boom!

http://www.MaguffinMicrowave.com

Maguffin Microwave wireless design consulting

 

[KevinNZ]

It standard practice our our industry to have N+1 burst disks and isolation valves under each disk. The isolation valves are locked open and have high-integrity administrative controls. Only one valve can be closed at a time.