Cavity pressure relief in LNG ball valves prevents dangerous pressure buildup from trapped liquid expansion if fluid vaporizes in closed cavities between seals. Pressure relief mechanisms or self-relieving seat designs prevent overpressure that could cause seal damage, body rupture, or dangerous pressure releases when valves are operated. Material traceability for LNG valve seals doc... https://globalsealstech.com/product-category/oil-gas-seals/api-6d-ball-valve-and-lng-seals/