When is a PSV required? 1

[ipocoyo]

Does anybody know which standard talks about when a PSV is required? My plant has a 1300L desiccant dryer fitted with a PSV, while the other 190L dryer does not.

 

[georgeverghese]

Equipment fabricated in accordance with ASME pressure vessel code must be fitted with PSV as required in some Code appendix. There would be similar rules with other similar national pressure vessel codes. Firecase PSV is not required for piping.

 

[mk3223]

Also, the pressure equipment may be part of the overall system protected by a PSV, instead of having its own PSV protection.

 

[MJCronin]

While the above statements are true, I would like to point out that the need for pressure protection should be based on a quality HAZOP done for all credible system upset and failure scenarios.

Pressure protection can take the form of PSVs, rupture discs, pressure relief panels and frangible roofs...

MJCronin
Sr. Process Engineer

 

[RVAmeche]

In my experience if you have a pressure vessel with MAWP > 15 psig, you'll likely need to provide a PSV or have calculations on hand showing you considered all the scenarios and the system is protected by design. Some states have size, pressure, and temperature exemptions so maybe the 190L dryer falls into that category (below 150 psig, less than xx dimensions, less than 300F, for example). Alternatively I've had projects where we did calculations showing the dryer was protected by design and an OSHA or NB inspector said "I don't care, add a PSV"

 

[Latexman]

When a pressure vessel is protected by design (ASME Code Case 2211), it may be wiser, faster and less expensive in the long run to put a small PSV on it anyway. My understanding of Code Case 2211 indicates it is quite onerous to meet Code requirements to not have a relief.

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

 

[moltenmetal]

Remember that what is required is a passive layer of pressure protection, NOT A PSV per se. A rupture disk, buckling pin device, or even a liquid leg of sufficient depth are all permitted as relief devices in satisfaction of both ASME VIII's code requirement and, more importantly, good engineering design. Replacing this passive layer of protection with an active layer of protection of similar calculated availability is difficult but possible.

 

[loilfan]

In Alberta, Canada, our jurisdiction (ABSA) has given rules for registering a system that is OPPSD (Overpressure Protection by System Design). See AB-525 for more info.

This of course is only Alberta-specific, but it shows what we do here.

 

[PRVBoss]

Your PHA will tell you when a PRV is required from a process safety perspective. Equipment design standard (ASME, API, etc.) will indicate when a PRV is required for code requirements. Your local oversight and inspectors (OSHA/NB) will tell you when a PRV is required (or missing) for compliance.