OVERPRESSURE PROTECTION AND RELIEF VALVESProcess Training School 2004/ Ti!eTa"leIn#ro$%c#ionCa%ses o& O'er(ress%reCalc%la#ion o& Relie& Loa$sRelie& Val'e Si)ingT*(es o& Relie& Val'esRelie& Val'e Ins#alla#ion+%es#ionnaire ,ha# is Press%re Relie&- A pressure relief device is a SAFET. device designed to protect pressurised systems during an /o'er(ress%re e'en#01o'er(ress%re e'en#refers to any condition which would cause the system pressure to increase beyond the specified design pressure or maximum allowable working pressure. Safety devices are used to protect the equipment and the lives of personnel by removing excess volume from the system safely to prevent overpressure. Safety !elief valves are the "#$%&A$' protection (last device remaining to prevent a catastrophic failure). As safety valves have to be reliable there are many codes and standards written to control their design and application. Co$es2 S#an$ar$s 3 Prac#ices AS4E 5 6oiler 3 Press%re 'essel Co$e7 A!erican Socie#* o& 4echanical Engineers)AS&' code provides specific rules re overpressure protection * design+ set pressures.Sec % , -ower .oilersSec /%%% , -ressure /essels.01.1 , -ower piping * .01.0 , -rocess -iping API 5 A!erican Pe#role%! Ins#i#%#e2A-% have worked to standardise the ratings and si3es of -!/4s25eveloped a series of standard inlet orifice si3e and outlet combinations that are used throughout the industry which are represented by 16 standard letters from 5 (smallest) to $ (largest)27 orifice is 1.89: in8.$his is the area used in A-% calcs to calculate the flow through this orifice. Co$es2 S#an$ar$s 3 Prac#ices API 5 A!erican Pe#role%! Ins#i#%#e2A-% ;8 , ?langed steel -!/s2A-% ;8: , Seat tightness of -!/s2A-% 8