Since the seat of the API 6D fully welded ball valve is made up of a carbon teflon seal ring and a disc spring, it is adaptable to changes in pressure and temperature and will not produce any leakage in the marked pressure and temperature range. Fully welded ball valves are widely used in domestic steel mills, petroleum, chemical, gas, boiler, paper, textile, pharmaceutical, food, ship, water supply and drainage, energy, polysilicon, electricity and so on.