August 10, 2020

Cryogenic valve body material selection

The design of the cryogenic valve has the following requirements, depending on the conditions of use:

1) The valve should have long-term working ability in low temperature medium and ambient temperature.

2) Valves should not be a significant source of heat for cryogenic systems. This is because the inflow of heat, in addition to reducing the thermal efficiency, such as excessive inflow, will also cause the internal fluid to evaporate rapidly, causing abnormal pressure rise, posing a hazard.

3) The low temperature medium should not have a detrimental effect on the operation of the wheel and the sealing performance of the packing.

4) Valve assemblies that are in direct contact with the cryogenic medium shall have an explosion-proof and fire-resistant structure.

5) Valve assemblies that operate at low temperatures cannot be lubricated, so structural measures are required to prevent friction from scratching.

Material selection for cryogenic valve structure

When selecting the host material, first select materials suitable for working at low temperatures. Aluminum does not exhibit low-temperature brittleness at low temperatures, but the hardness of aluminum and aluminum alloys is not high, and the wear resistance and scratch resistance of aluminum sealing surfaces are poor. Therefore, the use of low-temperature valves has certain limitations, only in low pressure and Used in small diameter valves.

Materials that work at low temperatures are guaranteed to have low temperature properties, primarily to ensure their cold impact strength. The trim must be properly selected to have sufficient cold impact strength to prevent breakage. Alloy steels of C and Cr quickly lose their impact strength at temperatures below -20 ° C, so the use temperatures are limited to -30 ° C and -50 ° C, respectively. Nickel steel containing 3.5% Ni can be used at -100 ° C, and nickel steel containing 9% Ni can be used at -192 ° C. Austenitic stainless steel, nickel, monel, Hastelloy, titanium, aluminum alloy and bronze can be used at lower temperatures (-273 ° C).

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