Subsea wellhead seals per API 6A use metal-to-metal with elastomeric backup. Hydraulic connectors lock in 60 seconds. In 18-3/4" 10M systems, they seal 10,000 psi. ROV torque tools verify preload. This enables tiebacks. https://globalsealstech.com/product-category/oil-gas-seals/api-6a-wellhead-equipment-seals/