Isolation valve for a Rupture Disc 1

[ashtree]

Would it be normal to put an isolation valve before a rupture disc to allow maintenance etc. to occur without shutting the plant down. I am talking about a water treatment installation where the rupture disc is installed as a last line of defense if all else fails on a pressure manifold.

My gut feel tells me no, because if the disc is isolated even for a short period than the protection it offers is lost.
But discs need to be checked and replaced from time to time so there would be a temptation to put an isolator before the rupture disc.
Is there some definitive guidance somewhere about this issue?

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[LittleInch]

Sounds identical to this post

https://www.eng-tips.com/viewthread.cfm?qid=479775

Either you need two or program any inspection in for a shut down.

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

 

[ashtree]

Thanks LI. The link was useful and supported what I was thinking.

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[TBP]

I've seen ammonia systems that had a 3-way quarter-turn valve under two safety valves. Operating the valve opened the inlet of one safety while simultaneously isolating the other.

 

[The Obturator]

You want to look at Change Over Valves that are normally used with 2 Pressure-relief Valves - Here one PRV is live/on-line the other closed off for maintenance or standy by. Change over valves are used where no system shutdown is required and/or foul service where the PRV requires cleaning often. There is no reason why you can't use such a valve with rupture discs only. API-520 Part II Documents this type of set up as 100% spare relieving capacity.

*** Per ISO-4126, the generic term 'Safety Valve' is used regardless of application or design ***

*** 'Pressure-relief Valve' is the equivalent ASME/API term ***