Today, XINLIANTONG will take you to understand the selection rules of materials for industrial cryogenic valve parts, hoping to help everyone understand industrial cryogenic valve better.
Material Selection of industrial cryogenic valve body, bonnet, valve seat and gate:
The selection principles of these main parts materials are roughly: ferritic steel is selected when the temperature is higher than -100 °C; austenitic stainless steel is selected when the temperature is lower than -100 °C; appropriate materials are selected according to the lowest operating temperature during design.
Material selection of industrial cryogenic valve stem and fasteners:
When the temperature is higher than -100°C, the valve stem and bolts are made of alloy steel such as Ni, Cr-Mo, etc. After proper heat treatment, the tensile strength can be improved and the thread bite can be prevented. When the temperature is lower than -100°C, it is made of austenitic stainless acid-resistant steel. However, the hardness of 18-8 acid-resistant steel is low, which will cause the valve stem and packing to rub against each other, resulting in leakage at the packing. Therefore, the surface of the valve stem must be chrome-plated, or nitrided and nickel-plated with phosphorus to improve the surface hardness. Thermal spraying process can also be used to spray wear-resistant and corrosion-resistant alloys such as molybdenum and STL on the surface. In order to prevent the nut and the bolt from being seized, the nut is generally made of Mo steel or Ni steel, and the surface of the thread is coated with molybdenum disulfide.
As the temperature decreases, the shrinkage of fluoroplastics will be large, which will reduce the sealing performance and easily cause leakage. Asbestos packing cannot prevent seepage leakage. Rubber is swellable to natural gas and cannot be used at low temperatures. In the design of cryogenic valves, on the one hand, the structural design ensures that the packing works at a temperature close to the environment. For example, a long-necked bonnet structure is used to keep the stuffing box as far away from the low-temperature medium as possible. On the other hand, consideration should be taken when selecting packing Low temperature properties of packing. Cryogenic valves generally use asbestos packing impregnated with tetrafluoroethylene.
Flexible graphite is an excellent sealing material. This material is impermeable to gas and liquid, has 10%~15% elasticity in the thickness direction, and can achieve sealing with lower fastener pressure. He has self-lubricating properties, and it can be used as a valve packing to prevent the wear of the packing and the valve. The
service temperature range of flexible graphite filler is -200~870℃.
Industrial Cryogenic Valve Supplier - XNLIANTONG
Chengdu XinLianTong cryogenic equipment Co.,Ltd founded in 2006,We are the scientific and technological enterprise mainly engaged in the manufacture and development of cryogenic equipment, such as cryogenic pipes, cryogenic valve, cryogenic vessel etc. Our products are widely used in metallurgical industry, petrochemical, electronics, biology, medicine, automotive industry cryogenic process, high (low) temperature superconductivity, food & pharmacy process, chemical application. Sincerely look forward to you becoming our partner.
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