At -162°C, LNG turns ordinary valve engineering upside down. Carbon steel becomes brittle, elastomers stop sealing, trapped liquid can burst a closed cavity as it vaporises, and every gram of heat leaking down the stem boils product away. Selecting a cryogenic valve is therefore less about pressure class and more about materials, geometry and proof testing.
Standard WCB carbon steel is limited to -29°C, and LCB low-temperature carbon steel to -46°C. Below that, austenitic stainless grades — CF8 (304), CF8M (316), CF3 and CF3M — remain tough down to -196°C thanks to their face-centred-cubic structure, with no ductile-brittle transition. Bronze and Monel appear in oxygen service for ignition resistance. Impact testing (Charpy V-notch at service temperature) should be specified for pressure-boundary parts.
Cryogenic valves carry a gas column extension between body and stuffing box. Its job is to keep the packing warm — above roughly 0°C — so it stays elastic and seals. BS 6364 and MSS SP-134 set minimum extension lengths by size and temperature; typical LNG valves use 250–600 mm. The valve must be installed with the bonnet within about 45° of vertical so the vapour column stays put.
A closed ball valve traps liquid in its body cavity. In cryogenic duty that liquid warms, vaporises and can multiply cavity pressure many times over. Trunnion designs use self-relieving seats; floating-ball designs need an upstream vent hole in the ball or a body relief route. Confirm the relief method on the datasheet — it defines which side is the sealing side.
PTFE and reinforced PTFE remain serviceable to -196°C and are standard for soft seats. PCTFE (Kel-F) offers lower cold flow for higher pressures. Graphite serves both as fire-safe secondary sealing and for metal-seated designs. Standard NBR/FKM O-rings are unusable — lip seals or spring-energised PTFE take their place.
Ambient testing proves little about behaviour at -196°C, so reputable cryogenic valves are type-tested (and often production-tested) per BS 6364 or ISO 28921: the valve is submerged in liquid nitrogen, cooled until stable, then seat- and shell-tested with helium at temperature. Allowable seat leakage is measured in bubbles per minute of helium. Ask for the cryogenic test report, not just the ambient API 598 certificate.
VTXFLOW manufactures cryogenic ball, gate, globe and check valves to -196°C with BS 6364 testing in-house. Send your LNG or industrial-gas datasheet for a technical proposal within 24 hours.