Spring-energized PTFE seals dominate stem and body applications in API 6D LNG valves. U-shaped PTFE jackets with stainless or Inconel springs maintain sealing force at cryogenic temperatures where elastomers become brittle. They achieve fugitive emission levels below 50 ppm per ISO 15848-1 https://globalsealstech.com/product-category/oil-gas-seals/api-6d-ball-valve-and-lng-seals/