Metal seated Ball Valves are preferred when the operating temperature is typically above 250 deg C, where the soft seats fail. The ball made of SS304 / SS316 is either coated with Nickel (by Electroless Nickel Plating) or hard faced with Stellite, depending upon the operating temperature and pressure. HVOF coating can be offered on balls and seats for temperature above 500 deg C. This is necessary to withstand continuous rubbing with hard metal seats. Stems are usually made of 17-4 PH Stainless Steel. Metal seated ball valves are designed to withstand both high temperature and pressure. The surfaces of both seat and ball are hand lapped to get the perfect mating to achieve Class V/ Class VI leakage. To compensate for thermal expansions, inconel springs are used.