EGT01;
I agree with the first half of your statement, that "relief valves in vapour service will achieve full lift by the time they reach 10% overpressure" (single, non fire case valve). However later on you say that you should get the same calculated required area whether you have set = 60 and...
Does anyone know of any situation where it would be required (or beneficial) for process reasons or otherwise, to have a pressure safety valve set at significantly less than MAWP, and hence allow overpressure to exceed 10% (for single, non fire case valve).
To allow overpressures >10% when...
EGT01,
1. Apologies, code does not prohibit one from sizing relief valves based on overpressure higher than 10% (21% for fire)if set pressure < MAWP.
2. My original question however was more one of curiousity as to the basis of these values (10% and 21% ACCUMULATION)which is a question that...
Does anyone have any info. on the following:
1. What is the basis for the 10% allowable overpressure specified by API520? Is it to do with the 0.9 derating factor used by vendors to determine capacity?
2. What is the basis for 21% allowable overpressure for 'fire case' relief valves.
3. Why...
