10 times operating no relief?
10 times operating no relief?
(OP)
I remember hearing that if your design pressure is ten times your operating pressure you do not need relief on that vessel. Is that true. I have some small portable filters that are normally connected to other equipment that have relief but sometimes they are sitting valved in with liquid in them. I am just concerned about the fire case.
Anyone have a reference on the 10x statement? Or am I all wet?
Regards
StoneCold
Anyone have a reference on the 10x statement? Or am I all wet?
Regards
StoneCold





RE: 10 times operating no relief?
I guess a similar thing might happen with a boiling liquid fire case. For example a propane tank that operates at 200 psia and 565 K and the vessel is rated at 1000 psia. As heat is added, the propane boils and the pressure goes up to 616 psia and 205 F. The tank has not started to see a significant loss in strenght and it is still below the set pressure of 1000 psia and it is now a supercriticle fluid. The pressure must increase to 1000 or 1.5 times the pressure. Then at 1000 psia, the temperature will be 1.5 * (205 +460)-460 = 537 F, somewhere between the time the pressure is increasing from 616 to 1000, the temperature goes from 205 to 537 F, the metal will weaken enough that it may fail at a lower pressure than the relief valve would open. (all you hardcore guys, don't jump on the above for not correcting for compressibility, especially above the criticle point, this only an simple example).
This is an extreme cases and one could argue the need for a psv with this system. Aw, but what about blocked flow, tube failures, control valve failure cases?
RE: 10 times operating no relief?
Good luck,
Latexman
RE: 10 times operating no relief?
The only time you do not need a PSV is when the vessel pressure rating is more than the pressure can ever get to in the vessel (absolutely, the pressure will not rise to meet the vessel's pressure rating). In this scenario, you do not need a PSV.
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RE: 10 times operating no relief?
Thanks
StoneCold
RE: 10 times operating no relief?
"Most knockout drums and seal drums are operating at relatively low pressures. To ensure sound construction, a minimum design gauge pressure of 345 kPa (50 psi) is suggested for knockout drums in subsonic flare or other low-pressure applications. A vessel with a design gauge pressure of 345 kPa (50 psi) should not rupture if a deflagration occurs. Stoichiometric hydrocarbon-air mixtures can produce peak explosion pressures on the order of seven to eight times the absolute operating pressure. Most subsonic-flare seal drums operate in the range of gauge pressure from 0 kPa to 34 kPa (0 psi to 5 psi)."