Safety relief valve requirements for surge talnks

[EEAutomEng]

It is my understanding that a safety relief valve must be installed on all surge tanks to prevent mishaps due to possible failure of the compressor to shut down. If ASME code requires this, then how do I size the valve? I have been told that the scfm rating of the valve should exceed the output rating of the compressor.

 

[psafety]

JMBurgess,
Can the compressor produce pressure exceeding the MAWP of the vessel? If so, and the vessel can be isolated I would determine a valve area that would limit the pressure to the MAWP of the vessel or lower (assumes this vessel is the weak link). I would then size a valve based on external fire exposure API-521 (I think) and select the larger of the two.
don coffman

 

[EEAutomEng]

It would be safe to assume that the vessel is the week link in the system because it is going to be in a metal fab/stamping plant where the compressors support large counterbalance systems. The MAWP is 200 PSI @ 650 F. What is API-521?

 

[chicopee]

THE SAFETY VALVE SHOULD HAVE A SET PRESSURE EQUAL TO OR LESS THAN THE mawp OF THE SURGE TANK. THE RELEIVING CAPACITY OF THE SAFETY SHOULD NOT BE LESS THAN THE COMPRESSOR FREE AIR DELIVERY NORMALLY RATED AT SCFM.

 

[psafety]

chicopee,

Agree with set pressure, but why (assuming potential over-pressure is the relieving case) should the relief area be sized for complete capacity vs. capacity exceeding the vessel MAWP?

don coffman

 

[chicopee]

Massachusetts law.

 

[chicopee]

and also insurance companies requirements

 

[psafety]

JMBurgess,
Right or wrong; if in Mass or if your insurance carrier requires definitely do what is legal.