The seat is the ball valve's defining wear part, and the soft-vs-metal decision drives leakage class, temperature limit, torque, actuator size and price all at once. Specifying metal seats "to be safe" can double the valve cost and actuator budget; specifying soft seats past their limits destroys them in weeks.
A soft-seated ball valve uses machined polymer inserts — virgin PTFE to about 180°C, glass- or carbon-reinforced RPTFE to about 230°C, and PEEK towards 260°C with far higher pressure capability. The polymer conforms to the ball microscopically, giving FCI 70-2 Class VI bubble-tight shutoff at low torque. Limits: temperature, abrasive particles that embed in the polymer, and cold flow under continuous high load.
A metal-seated ball valve runs hard-faced seats — Stellite, chromium carbide or tungsten carbide sprayed and lapped to the ball — for service to 550°C and media laden with catalyst fines, sand or scale. Typical achievable tightness is Class IV–V (a small measurable leak); premium lapping can reach Class VI at a price. Expect two to three times the operating torque of a soft seat, which cascades into a larger actuator.
Standard soft-seated valves for hydrocarbon service are built fire-safe to API 607 / API 6FA: if the PTFE burns away, a secondary metal lip contacts the ball and limits leakage to survivable rates. This is not a metal-seated valve — tightness after a fire is emergency-grade — but it removes fire exposure as a reason to abandon soft seats.
VTXFLOW machines both seat systems in-house across floating and trunnion designs and tests every valve to API 598. Describe your medium and temperature and our engineers will confirm the seat material and leakage class in the quotation.