API 6A establishes four Performance Specification Levels (PSL 1-4) with increasingly rigorous quality, testing, and documentation requirements. PSL-3 and PSL-4 apply to critical wellhead equipment requiring enhanced material traceability, non-destructive examination, and comprehensive seal qualification testing. https://globalsealstech.com/product-category/oil-gas-seals/api-6a-wellhead-equipment-seals/