API 6A weld-neck flange seals use lens ring gaskets. Compact design suits high-pressure. In 3-1/8" 15M connections, they seal 15,000 psi. Weld prep per ASME B31.3 ensures strength. This integrates with flowlines. https://globalsealstech.com/product-category/oil-gas-seals/api-6a-wellhead-equipment-seals/