1. The minimum allowable temperature of the cryogenic valve.
2. Metallic materials at low temperatures to maintain the mechanical properties of the working conditions, especially the impact toughness, relative elongation and organizational stability.
3. In case of low temperature and without oil lubrication, it should has a good abrasion resistance.
4. It should has good corrosion resistance.
5. If it is welded connections, we need to consider the welding performance of material.
6. How to select the material of valve body, valve cover, valve seats, valve disc.
7. Usually, we can generally choose ferritic steel when the temperature higher than -100°C for our normal material selection principles.
8. If the temperature is below -100°C, we can choose austenitic steel; for low pressure and small diameter valves, we can also used copper and aluminum materials. We should select the suitable material in accordance with the lowest working temperature.
9. For the stem and the fastener material, if the temperature higher than -100°C, it should be selected Ni, Cr-Mo alloy steel plus proper heat treatment to improve the tensile strength and to prevent the thread bites.
10. When the temperature is below -100°C, we should use the austenitic stainless acid-resistant steel. But the hardness of 18-8 acid-resistant steel is low, will cause the scratches between the stem and packing, so that it may leak. Therefore, the stem surface must be hard chrome plating (coating thickness 0.04-0.06mm), or nitride and nickel-phosphorus plating to improve the surface hardness.
11. To stop the nuts and bolts to be jammed, nuts generally use Mo steel or Ni steel, meanwhile to coat with molybdenum disulfide in the thread surface.