I posted this question a while back and decided from the response that I needed to go away and think about what I was asking.

I have attached a pdf sketch of the basic setup im designing. Basically a pump delivers a chemical from a storage vessel to a remote process. The delivery line is protected against over-pressurisation by a relief line. This is just a small line designed to relieve excess pressure mainly caused by the pump.

If a fire were to occur then the fluid would vaporise in this line and could possibly cause the pipe itself to rupture. I have been told to design it to the relevant code to ensure this doesnt happen

I don't know a great deal about pressure relief but I have obtained a copy of API 510 and used this to size a relief device for the vessel. Should an additional device be added to protect the line?? this would seem to be going too far - and where along its length would the device be best installed? Also does there actually exist a code specifically for protecting pipework.

Thanks for any help in advance

I hope you are referring to API RP520 and not API 510. API 510 is the Pressure Vessel Inspection Code: In-Service Inspection, Rating, Repair, and Alteration.

You still don't give enough information for any of us to stick our necks out and give you a definitive response. So I will answer as such. If the relief line terminates at the vessel nozzle without a dip tube, which I would expect, and is therefore in the vessel vapor space, then you should not need an additional PSV. The one you show on the vessel will do the job if sized properly.

JE:

API 510 is titled: Pressure Vessel Inspection Code - In-Service Inspection, Rating, Repair, and Alteration.
Normally, we would use API 520, “Sizing, Selection, and Installation Of Pressure-Relieving Devices in Refineries”, Parts I & II together with API 521, “Guide for Pressure-Relieving and Depressuring Systems”.

Your sketch begs the question as to why is the PSV for the pump’s discharge located so far away from the pump – 100 meters? Are you failing to show installed block valves and/or check valves in the discharge line? This is an important point to evaluate in the event the fluid is trapped in the line with a heat source trying to vaporize it.

Does your fire scenario dictate that the pump is immediately shutdown and blocked off? You say you presently have a PSV installed to protect the line in case of overpressure due to the pump’s discharge. Is this a positive displacement pump or a centrifugal pump? Where, precisely is the PSV located? - at the pump’s discharge?

Are you mandated in relieving the mystery fluid back to the tank? Why not relieve directly to the atmosphere?

If I’m raising a lot of questions, believe me that others that follow will do likewise. We really don’t know that much about your system or the way that you operate it – and even less about how you used API 510 to design the required PSV size.

Can you furnish specific data as to your system? The sketch is great, but we don’t know the fluid, the installed valves, the need to locate the PSV where it is shown, etc., etc.

I did mean API520 - sorry

Thanks very much for your help - I will get hold of a copy of API521 as this seems to be something i need.
Im very sorry for the rather obvious 'squirrelling' of information. Regrettably a client confidentiallity agreement prevents me giving full details and so I have to accept that this prevents me getting a full solution.

Once again many thanks for your help