PCTFE (Kel-F) is the preferred soft seat material for LNG ball valves. It retains toughness at -196°C, exhibits low thermal contraction, and provides extremely low leakage rates. Seats are precision-machined and spring-loaded to compensate for thermal shrinkage and maintain contact pressure during cooldown https://globalsealstech.com/product-category/oil-gas-seals/api-6d-ball-valve-and-lng-seals/