API-RP-576

4.8.3 Limitations
Pilot-operated safety-relief valves are not generally used as follows:
a) in service where fluid is dirty, or where there is a potential for fouling or
solidification (e.g. hydrates, wax, or ice) in the pilot or sensing line unless
special provisions are taken (such as filters, sense line purging, etc.);
b) in viscous liquid service, as pilot-operated valve operating times will increase
markedly due to flow of viscous liquids through relatively small passages
within the pilot;
c) with vapors that will polymerize in the valves;
d) in services where the temperature exceeds the safe limits for the diaphragms,
seals, or O-rings selected;
e) where chemical compatibility of the loading fluid with the diaphragms, seals,
or O-rings of the valves is questionable;
f) where corrosion buildup can impede the actuation of the pilot.
Fion Zhnag/ Charlie Chong