Why PSV are leaking while in service ?? 2

[hniaboujemaa]

Any though ?

Regards.

 

[MortenA]

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

Best regards

Morten

 

[moltenmetal]

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.

 

[MortenA]

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

 

[hniaboujemaa]

Thanks guys for your feedbacks.

Mouss

 

[moltenmetal]

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!

 

[hniaboujemaa]

Interesting, moltenmetal !
Thanks for sharing this

 

[don1980]

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.

 

[JimCasey]

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.