Hi All,
I have question regarding multiple safety valves, in my case two safety valves.
PSV A set pressure : 10 barg
PSV B set pressure : 10.5 barg (105% of PSV A set pressure as per API 520)
I have several scenarios on these two safety valves. One of the scenarios (non-fire scenario, not governing scenario) can be handled with PSV A (PSV A has adequate capacity to prevent overpressure).
My question: is it possible to consider only PSV A safety valve for this scenario and consider 10% pressure accumulation (instead of 16% pressure accumulation for multiple safety valves)?
My own opinion:
In reality additional safety valve (PSV A) will be partially open (if not fully open) because;
- Relief pressure (110% of Design Pressure) will be higher than set pressure of PSV B (105% of Design Pressure)
- Based on API520 Part I, Para. 4.2.1.2.4: “…Typically, the valve will suddenly surge to 50 % to 100 % lift at 2 % to 6 % overpressure…”.
If we consider that only one valve with lower set pressure (PSV A) is fully open then we may overlook potential risk of chattering since both safety valves will be open. I believe most conservative way is to consider both valves open (therefore, 16% pressure accumulation on top of design pressure as relief pressure).
Please let me know how you think about it.
Regards,
ARM
Edited by ARM, 16 May 2017 - 02:15 AM.