Pressure relief valve maximum allowable accumulated

The pressure drop allowed through the inlet and discharge lines is unlimited as long as the capacity of the line is adequate for the relief requirements. That is, at the required flow rate the vessel pressure must not exceed the maximum allowable accumulated pressure. In sizing a safety disc, it is usually assumed that the entrance loss at the nozzle is the governing restriction insofar as capacity is concerned. Thus the effective orifice area is considerably larger than the effective orifice area of a safety valve of the same pipe size. Consequently,... 

Accumulation pressure increase over the maximum allowable working pressure of the vessel during discharge through the safety or relief valve, expressed as a percent... 

If the relief valve is sized correctly, then the maximum pressure that can accumulate is 110% of the maximum allowable working pressure, P (ASME BPV Code Sec. VIII D.l UG-125). At this point there is no further accumulation of pressure and dp/dt = 0, hence. 

Accumulation for pressure vessels protected by multiple relief valves should not exceed 16% of the maximum allowable working pressure (MAWP), except in case of fire. 

---