Material Selection for Cryogenic Valves

Material Selection for Cryogenic Valves

The working fluids of cryogenic valves are not only cold but also often toxic, flammable, or explosive, as well as highly permeable. This dictates many special requirements for valve materials. The mechanical properties of steel at cryogenic temperatures differ from those at room temperature. Besides strength, the most important performance characteristic of cryogenic steel is its low-temperature impact toughness. This low-temperature impact toughness is related to the material's brittle transition temperature; the lower the brittle transition temperature, the better the low-temperature impact toughness. Metals with a body-centered cubic lattice, such as carbon steel, experience low-temperature brittleness, while the impact toughness of metals with a face-centered cubic lattice, such as austenitic stainless steel, is largely unaffected by low temperatures.

The materials used for pressure-resistant components such as the valve body and bonnet of cryogenic valves typically utilize tough materials with good low-temperature strength. Factors such as weldability, machinability, stability, and cost-effectiveness must also be considered. Engineering companies typically design for low-temperature grades of -46°C, -101°C, and -196°C. Low-temperature carbon steel is generally used for the -46°C low-temperature grade, while 300 series austenitic stainless steel is generally used for the -101°C and -196°C low-temperature grades. This type of stainless steel has moderate strength, good toughness, and good processing properties. According to ASMEB31.3, the lowest applicable temperature of commonly used materials for low-temperature valves.