Technical Requirements and Material Selection Standards of Cryogenic Valves | EN |

Technical Requirements and Material Selection Standards of Cryogenic Valves

According to working conditions, design requirements of cryogenic valves are listed below.
A cryogenic valve is supposed to work for long periods of time with cryogenic media and under low temperature.

A cryogenic valve cannot become an main heat source in the cryogenic system because the flow of heat can reduce thermal efficiency. At the same time, if there are too many fluids flowing into the valve, the fluid inside the valve will evaporate rapidly, resulting in the abnormal increase of valve pressure and potential danger.

Cryogenic media should not have harmful effects on the hand wheel and sealing performance of the cryogenic valves' packing.

The components of the cryogenic valve in direct contact with cryogenic media are supposed to have structures with explosion-proof and fireproof. 

Since the components of the cryogenic valve can't be lubricated, it is necessary to adopt a certain structure for preventing the damage of components.

The materials of the cryogenic valve body.
It is necessary to think about the metal material for the cryogenic valve body. Except the metal material with the face-centered cubic lattice, such as the Austenitic steel, copper and aluminum, general steel gets low-temperature brittleness under low temperature, reducing the strength and operating life of the cryogenic valve. The first priority of selecting valve body materials is ensuring the low-temperature resistance of the material. Aluminum is such a kind of material that it does not have the low-temperature brittleness under low temperature. However, since the low hardness of aluminum and aluminum alloy, the aluminum sealing surface has the poor wear resistance and scratch resistance, which limits the applications of the cryogenic valve. Therefore, aluminum is only used for the small-diameter cryogenic valve under low pressure.

The working performance of valve materials under low temperature must be guaranteed, especially the impact strength. In order to prevent breakage, the components inside the cryogenic valve are necessary to have high impact strength under low temperature by means of suitable materials.

Ni steel with 3.5% Ni is adaptable to the working temperature down to -100℃ while Ni steel with 9% Ni is suitable for the working temperature down to -192℃.

Austenitic stainless steel, Ni, Monel, Hastelloy, titanium alloy, aluminum alloy and bronze are applied to working conditions at operating temperature as low as -273℃.

Besides, here are some other factors worth considering:  
The minimum operating temperature of cryogenic valves should be considered.

It is necessary to keep the mechanical properties of metal materials under low temperature, especially impact strength, relative elongation and microstructure stability.

Without lubricating oil and under low temperature, the cryogenic valve is supposed to have  great wear resistance.

The cryogenic valve is supposed to have good corrosion resistance.
It is necessary to consider the welding performance of the valve material before welding.