FFKM perfluoroelastomer seat seals (Kalrez® 0090, Chemraz® 605) dominate 15,000–20,000 psi HP/HT gate valves. Rated to 625°F continuous and passing NORSOK M-710 RGD testing, they survive decades in aggressive sour gas, CO2 injection, and amine inhibitor environments without degradation. https://globalsealstech.com/product-category/oil-gas-seals/api-6a-gate-valve-seals/