FFKM (perfluoroelastomer) seals such as Kalrez® 0090 and Chemraz® 605 are standard for extreme HP/HT wellheads exceeding 450°F and 15,000 psi. These compounds survive 10-year continuous exposure to sour gas, steam, and aromatic hydrocarbons while passing API 6A PR2F qualification with zero leakage in 20,000-psi gas tests https://globalsealstech.com/product-category/oil-gas-seals/api-6a-wellhead-equipment-seals/