Is a PSV required if there are no credible scenarios? 3

[ipocoyo]

Hi All,
My site consists of 3 air compressors connected in parallel which are connected to an air receiver. The air compressors each have a maximum operating pressure and cut off pressure of 10 bar(g). All the equipment in the compressed air system are rated with a design pressure of 16bar(g). According to API 521, the only credible scenario of over-pressurisation happening is due to an external fire since the air compressors are located in a room beside the boiler. From my understanding, fitting a PSV for the event of an external fire is not regarded as sufficient protection, but does buy extra time in the event of an over-pressurisation. The compressor system will still be lost due to the external fire.

My question is, is it still a requirement to fit a PSV if the only credible scenario is due to an external fire (which does seem unlikely with the different controls in place)? My local standards states that “each pressure vessel shall be protected by a pressure-relieving device that shall prevent pressure from rising to more than 110% of the design pressure of the vessel.” This does seem a bit ridiculous since even the small filters (16bar(g)) are considered as a pressure vessel and thus requires a PSV. Is there anything that I can reference which states that if an event of over-pressurisation is unlikely then a PSV is not required?
Thank you!


Still an intern

 

[ipocoyo]

Hi don1980,

I want to point out from that clause that: "unless the equipment is intended to be protected by other protective devices within the assembly"
Would the code be met if there is a PSV located directly 2-3 meters away on the same line from the inlet of the filter?

Also, the receiver vessel (6000lt) attached downstream from the filters will also act as a buffer which would provide extra protection in the
event of an overpressure. So is a PSV really required to be attached to the filter? Overpressure protection is provided by system design.

Still an intern

 

[don1980]

Yes, relief devices can be mounted remotely as long as there's an open path between all the protected equipment and the relief device, and as long as the relief device is designed to prevent the protected equipment from exceeding it's allowable maximum pressure.