Pressure Vessel Size for Relief Requirements

[RJB32482]

Is there a section in API or ASME codes that state what size of a pressure vessel needs a pressure relief device? I am looking at requiring a small pressure vessel and wondering if the size I'm looking at needs a PSV? Could you tell me what section its in and the size if known?

Thanks.

 

[TangoCleveland]

ASME BPVC Sec VIII Div 1, para UG-125(a) says,
"All pressure vessels within the Scope of this
Division, irrespective of size or pressure, shall be
provided with pressure relief devices in accordance
with the requirements of UG-125 through UG-137. It
is the responsibility of the user to ensure that the
required pressure relief devices are properly installed
prior to initial operation."

Para U-1 describes sizes of vessels that are within the Scope of the Code. There are exclusions for small sizes and low pressures less than 15 psig.

Larry

 

[Ashereng]

Doesn't ASME Sect VIII also allow a vessel that is rated higher than the maximum pressure that can exist within the vessel to not have a PSV?

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
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[RJB32482]

I believe Ashereng is true, but I am looking at designing the pressure vessel to not have a relief valve for even the fire case. Fire cases will always have relief scenarios. I am looking at not having to relieve styrene anywhere since the vessel location will be ot 25 ft away from fire.

Thanks.

 

[TangoCleveland]

UG-125 (g) says "The pressure relief devices required in (a) above need not be installed directly on a pressure vessel when the source of pressure is external to the vessel and is under such positive control that the pressure in the vessel cannot exceed the maximum allowable working pressure at the operating temperature except as permitted in (c) above (see UG-98)."

My opinion is that UG-125(g) only says that the PSV doesn't have to be directly on the vessel; it doesn't say you don't need a PSV somewhere. I also think there's a lot of room for interpretation here.

Dig through UG-125 and see what you can find. There's also a Code Case 2211 that allows use of a "High Integrity Pressure Protection System" that uses instrumentation instead of a PSV to prevent overpressure. There's some discussion in thread292-149925.

I remember putting three 150 psig MAWP filter vessels in a service air system, where the compressor discharge PSVs were set at 138 psig. Management complained that my vessels didn't have individual PSVs set at 150 psig.

Since you're working with styrene, what pressures and temperatures are you dealing with? What size is your vessel?

Larry

 

[sethoflagos]

Two thoughts RJB32482:

If there isn't a handy relief disposal system nearby, can you direct the relief into a lower pressure system (eg downstream the outlet block valve) where adequate relieving facilities already exist?

Utilities systems often construct small simple vessels out of B31.3 pipe fittings to avoid ott code requirements (eg substituting say a large dripleg for a conventional knock-out vessel). I'm not sure this would be appropriate for styrene monomer though!