2 replies to this topic

Hi all,

I am new to PSV scenarios and sizing, so I am trying to get some clarification on fire scenario cases. I have 21 years of experience in operations, process control, and process engineering in chlor-alkali and hydrocarbons processing.

From reading API standard 521, the external pool fires and jet fires are discussed for fire case scenarios. The pool fire scenario requires flammable liquid pooling around the vessel. API standard 521 indicates that relief valves are not design for jet fire scenario (localized heating of the vessel wall). Do we need to consider a fire scenario of engulfing the vessel in fire due to 8" or larger natural gas piping system failure (gasket failure or flange failure) next to the vessel? System pressures operate from 400 psig to 1200 psig normally and the vessel (natural gas compressor suction scrubber) in question has flanged (RF) connections. We have had some minor leaks and fires on the positive displacement compressors and natural gas engines near the vessel.

We block in the process and vent the natural gas on high LEL or fire-eye detection in the area above.

Thanks,
CJL

[Lowflo]

That's a risk management decision for the client to make. There's no right or wrong answer. You obviously can't create a pool fire from a fuel gas header, but vessels at a higher elevation could be exposed to what looks a lot like a pool fire.

[rxnarang]

Designing for jet fire is another matter altogether. There are papers which can help you deign for such a case - one will need a lot of information on carbon steel failure temperatures, and then work around that to figure out the depressurisation rate. The depressirisation rate has to be faster than the decline in strength of the carbon steel plate. Googling for this will get you the papers.

Regards