You can try a mechanical Lift Indicator arrangement for this purpose. If the medium is at a higher temperature than atmospheric, then a thermocouple (temperature sensing element) at the outlet may serve your purpose.
Since the loading on the Valve seat in a Safety Valve is of Impact nature and Stellite is poor in withstanding Impact loads, generally Stelliting of Seats of a Safety Valve is not recommended.
Safety Valves are automatic pressure relieving devices actuated by the pressure upstream of the Valve and is characterised by means of a pop action. They are used for compressible fluid service eg. Steam, air etc.
Relief Valves are also automatic pressure relieving devices but they are...