Valves for LNG & Cryogenic Service

An extended bonnet (also called a top-entry or long-bonnet valve) has an elongated bonnet section that moves the stem packing away from the extremely cold process fluid. This prevents the packing material from being exposed to cryogenic temperature (where it would lose elasticity and leak), and prevents atmospheric moisture from freezing around the packing gland. The extension length is calculated based on the process temperature and the acceptable minimum packing temperature.

For LNG (−162°C) and liquid nitrogen (−196°C): ASTM A351 CF8M or CF3M (cast SS 316/316L) and ASTM A182 F316L (forged). For liquid CO₂ and −46°C service: ASTM A350 LF2 (forged low-temperature carbon steel), Charpy impact tested at −46°C. Standard A216 WCB carbon steel must never be used in cryogenic service below −29°C.

BS 6364 specifies the design and testing requirements for cryogenic valves. The key test is a gas bubble (helium/nitrogen) seat leakage test performed at the design cryogenic temperature while the valve is immersed in liquid nitrogen or cryogenic fluid. This verifies the seat sealing integrity is maintained at operating temperature. Extended bonnet valves are tested with the bonnet in the ambient zone to simulate installed conditions.

Yes. All cryogenic valves supplied by Vajra Industrial Solutions include EN 10204 3.1 material test reports showing Charpy V-notch impact test results at the specified test temperature (typically −46°C for LF2 and −196°C for stainless grades). Where BS 6364 cryogenic testing is required, we arrange this at approved test facilities with documented test reports forming part of the valve documentation package.