API 6A HH-NL material class seals are fully NACE MR0175/ISO 15156 compliant for unlimited H₂S partial pressure. Special RGD-tested HNBR, FKM, and FFKM compounds prevent cracking during rapid pressure drops common in sour gas production and high-rate gas lift operations. https://globalsealstech.com/product-category/oil-gas-seals/api-6a-wellhead-equipment-seals/