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Why PSV are leaking while in service ??
2

Why PSV are leaking while in service ??

Why PSV are leaking while in service ??

(OP)
Any though ?

Regards.

RE: Why PSV are leaking while in service ??

maybe it simmers once in a while and the seat get dammaged?

Best regards

Morten

RE: Why PSV are leaking while in service ??

Because they always do- even the soft seated ones.

Want them to not leak?  Put a nonfragmenting rupture disc at the inlet, with a suitable vent and/or telltale between the two in case the disc gets a pinhole and leaks.  That is a major safety problem and cannot be ignored.

RE: Why PSV are leaking while in service ??

Moltenmetal: Why is it a _major_ safety problem? Assuming that hes got a flare/vent header thats purged i dont really see why the is a major safety problem, maybe not even a minor environmental problem - but i would like to learn here.

Thanks in advance

Morten

RE: Why PSV are leaking while in service ??

(OP)
Thanks guys for your feedbacks.

Mouss

RE: Why PSV are leaking while in service ??

You misread my post, MortenA.  The major safety problem is a rupture disc upstream of a relief valve with no telltale and vent.  In this case, a pinhole leak can pressurize the space between the disc and valve inlet- Murphy's Law saying that the valve itself will seal tighter than the hubs of hell in this case, while leaking freely all the rest of the time.  The resulting back-pressure on the disc ensures that the disc will NOT rupture at its set pressure.  Yeah, I'd call that a major safety problem!

RE: Why PSV are leaking while in service ??

(OP)
Interesting, moltenmetal !
Thanks for sharing this

RE: Why PSV are leaking while in service ??


The seat tightness requirements for API-526 PSVs is probably a lot looser than most people think. The leak test calls for a piece of tubing to be connected to the discharge, and submerged in a beaker of water. The acceptance criterion is 40 bubbles of leakage per minute.
 

RE: Why PSV are leaking while in service ??

Moltenmetal: Absolutely right that the tell-tale/vent is required between the RD and the SRV.  ASME says so.  So there's a primary safety consideration for life and property, also a safety consideration of the company checkbook if the authorities catch you in violation!  

Also, seat tightness depends upon available preload-it is bad practice to operate any higher than 90% of set pressure.   

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