API Low Temperature Valve Characteristics

Material selection

Main body materials: for low-temperature valves (-100 ℃ ~ -30 ℃) the main body materials are low-temperature austenitic stainless steel and low-temperature pressure parts with ferritic and martensitic steel. Ultra-low-temperature valves (-254 ℃ ~ -101 ℃) body materials must be selected face-centered cubic lattice of austenitic stainless steel, copper alloy or aluminum alloy.

Sealing materials: cryogenic valve closure parts are often cobalt chromium tungsten carbide surfacing structure. Soft seal structure, polytetrafluoroethylene can be used for temperatures higher than -70 ℃ cryogenic valve, polytrifluoroethylene can be used for -162 ℃ cryogenic valve.

Structural design

Lengthened bonnet: The structure of lengthened bonnet can protect the stuffing box and keep the temperature of the stuffing box above 0℃ to ensure the normal work of the packing, and at the same time, it is convenient to wind the cold-retaining materials.

Special valve flap: gate valve adopts flexible gate or open gate; flat seat of globe valve and needle valve, adopts plug-shaped valve flap, which can ensure that it can still maintain reliable sealing when the temperature changes.

Valve stem treatment: the valve stem needs to be chromium-plated, nickel-phosphorus-plated or nitrided to improve the surface hardness and prevent the valve stem from biting each other with the packing and the packing pressure sleeve to avoid damaging the sealing packing and causing leakage of the stuffing box.

Pressure relief design: In order to prevent abnormal pressure rise in the valve cavity, cryogenic gate valves, ball valves, etc. usually open pressure relief holes in the gate or ball, or through the design of pressure relief valve seat to realize the pressure relief of the valve cavity.