One possibility for consideration:
Relief valves are proportional flow devices whereas safety valves are full flow devices. Relief valves are thus intended for liquid service only and are frequently used to relieve from a higher pressure to a lower one (hydraulic systems for example). Such a...
In marine practice the superheater relief valves were always set to lift before the drum safeties in order to prevent overheating of the superheater bank tubing. If the drum relieves first then this could happen due to the residual heat or due to boiler firing not being fully shut down...
