I am very interested in learning API 520 and API 521 (everything about pressure relieving system). It is because that is the weakest point of me. I want to try make my understanding better, starting from pressure level.
I have heard and read so much about pressure terminology since years ago but still confusing until now. What was the MAWP, MOP, design pressure, set pressure, relieving pressure?
In this post I want to share what I read in API RP 521 (Guide for Pressure Relieving and Depressuring Systems). I read about some terminology in pressure level so that I hope I will not confuse about terms anymore.
Let’s see some terms in column Pressure Vessel Requirement.
1 – Operating Pressure
It is the pressure to which the vessel is usually subjected in service. A pressure vessel is usually designed for a maximum allowable working pressure that will provide suitable margin above the operating pressure to prevent any undesirable operation of the relieving device.
2 – Maximum Allowable Working Pressure
It is the maximum permissible gauge pressure at the top of completed vessel in its operating position for a designated temperature. It is basis for pressure setting of the pressure relief devices that protects the vessel.
3 – Design Pressure
It is at least the most severe condition of coincident temperature and gauge pressure expected during operation. It may be used in place of maximum allowable working pressure in all cases where the maximum allowable working pressure has not been established.
4 – Accumulation
It is the pressure increase over the maximum allowable working pressure of a vessel during discharge through the pressure relief device, expressed in pressure units or as a percent.
5 – Maximum Allowable Accumulated Pressure
It is the sum of the maximum allowable working pressure and the maximum allowable accumulation.