25k HPHT surface wellhead seals use double P-shaped FFKM elements with integrated anti-extrusion springs. This geometry survived 15 RGD cycles at 260°C/25,000 psi in Chevron’s Anchor field qualification, with zero leakage across the barrier during 72-hour hold periods post-decompression. https://globalsealstech.com/product/rgd-rapid-gas-decompression-o-rings/