There are many causes of overpressure. Every possible overpressure condition shall be reviewed to ensure overpressure protection device capacity is adequate to protect the system. The following picture presents the causes of overpressure.
For review whether this case applicable or not, check : is there any valve that possible closed? Or any control valves which is ‘fail to close’ position? is there any object that possible block the fluid flow ? If YES, it may be blocked and lead to pressure increase.
The required load capacity of PSV can be determined based on the mass balance in the system after block outlet occurred.
Here is just simple case.
For system which comprises of many vessel / separator with same design pressure, block outlet case is only considered for PSV in the most upstream location. When block outlet occurred at downstream the system pressure increase lead to open PSV at the upstream.
I think, it is better to explain by this picture
Therefore, for system with same design pressure, the block outlet only applicable for one PSV only.
My friend, that’s all, I can share to you today. Hopefully, this simple article useful for you.
Tomorrow is 6 April 2012, that is holiday for all of us;
I just want to say, happy holiday my friend, God bless you all.,,