With referance to: Pressure Level Relationships chart

Accumulation & Overpressure of PRV; 

When the Pressure Relief Valve (PRV) is active ( open):

-% of the excess pressure from the “system MAWP” is called “Accumulation”

-% of the pressure beyond the “set pressure” of the PRV is called “Overpressure”

 

PRV – Maximum Set Pressure & Accumulation of the ASME Code; 

According to ASME Code, Pressure Relief Valve (PRV) must have maximum Set Pressure and Accumulation not higher than the table (% MAWP) which will be divided into Nonfire Case and Fire Case for use in both PRV ( Single PRV) and Multiple PRVs