In addition, material selection of cryogenic valves should also think about factors below the problem: the minimum use of temperature of the valve; (2) metal material at low temperatures to maintain office conditions needed for the mechanical properties of Marine valve, especially the relative elongation, impact toughness, and group safe sex; (3) under low temperature and the status of the oilless lubricating oil thing, with satisfying the frictional resistance; (4) have satisfactory corrosion resistance; 5) Adjacent department sees fit and use of welding materials still need to think problems when welding performance. In cryogenic valves default, on the one hand, by the structure of presupposition to ensure packing under background temperature near the office, for example, consider appropriate and use the long neck cover structure, make the stuffing box. Temperature is below - 100 ℃ when deem appropriate, and the use of austenitic stainless acid-resistant steel production. 。 (3) pay the handwheel operation and low temperature medium error packing tightly closed performance initiation harmful effects. Ni content is 3. 5 one hundred percent of nickel alloy steel can be applied to - 100 ℃, 9 one hundred percent Ni content of nickel alloy steel can be applied to - 192℃。 Asbestos packing is no way to prevent leakage permeability. To avoid the nut and screw bite, nut common right and use the Mo steel or Ni steel, at the same time in the turnbuckle appearance with molybdenum disulfide. Q: a: forged steel cold by the valve selection of forged steel low temperature by the end of valve is suitable for use in cryogenic liquid handling facilities management system, a flexible switch, tightly closed tried-and-true unique place, can also be used for other low soft cryogenic media management system. Medium of low temperature by the valve is mainly refers to the use of temperature in 196 - - The low temperature of 150 degrees liquid medium in the system by the valve. But 18 - 8 acid-resistant steel hardness is low, can lead to stem and packing scratch each other, so that packing leak. Materials at low temperature in the office to ensure the low temperature performance, mainly is the guarantee the cold shock strength. 2, gasket, packing material selection of cryogenic valve: with temperature decrease, the fluorine molecular compound plastic shrinkage is very big, can make the tightly closed performance decline, easily moved. Aluminum will not reveal low temperature brittleness at low temperature, but because of the hardness of aluminium and aluminium alloy is not high, aluminum tightly closed surface wear and abrasion resistance is poor, so in the application of cryogenic valves have certain limit, only at low pressure and small diameter valve in use. ( 2) Body and bonnet, valve seat, disc ( Ram) The selection of materials, the material selection of a subject zero device principle is about: temperature above - At the beginning of 100 ℃ for ferritic steel; Temperature is below - At the beginning of 100 ℃ for austenitic steel; Low pressure and small valve can choose materials such as copper and aluminum. So, stem looks sure to hard chromium plating ( Plating thickness of 0. 04 - 0. 06mm) , or nitride and plating of nickel phosphorus treatment, surface hardness to growth. assembly (5) at low temperature in the office have no way of lubricating oil, so need to take treatment method of the structure, in order to avoid friction abrasion. Trims must be through the accurate material, make its have sufficient cold impact strength, ability to avoid disconnection. Austenitic stainless steel, nickel, monel alloy, hartz alloy, titanium, aluminum alloy and bronze can be applied to a lower temperature ( - 273℃) 。 A, cryogenic valves of the default requirement according to the using condition, cryogenic valve list by default has the following requirements: (1) the valve in the medium of low temperature and the area background temperature should have experienced a long period of time in the office. In default of this kind of valve, besides should follow the principle of common valves default, there is a little special requirements. Second, the material selection of cryogenic valves 1, cryogenic valve body material ( 1) Main body material selection factors from metallographic thinking about problems that should be thinking about problems, except in metallic materials possess face-centered cubic lattice of austenitic steel, copper, aluminum, such as ordinary steel under low temperature conditions will reveal low temperature brittleness, thus reducing the strength of the valve and to use fixed number of year of survival. Rubber is swelling, for liquefied natural gas at low temperature can't think right and use. Boron steel in below - C and Cr 20 ℃ moment soon miss impact strength, so use into temperature limit in - 30 ℃ and - 50℃。 When choosing the subject material must first choose material adapted to the low temperature in the office. Cryogenic valves, cryogenic valves, in particular, the office temperature is very low. This is because the calories inflows in addition to the low thermal reduction rate, such as flow too much, still can make inner fluid very fast evaporation, initiation of abnormal pressure, lead to danger. (4) direct contact with the medium of low temperature valve assembly should have explosion and fire prevention structure. (2) Industrial Valves is not strain are low temperature system of a hot objects significantly. ( 3) The valve stem and material selection of fasteners, temperature is higher than - 100 ℃, the stem and sees fit and use of Ni, screw material, Cr - Mo boron steel, such as the proper heat treatment, in order to increase the tensile strength and avoid turnbuckle bites, etc. At room temperature by the valve refers to the use of medium temperature - Between 40 ~ + 500 degrees, body of the material is also different. The preset according to minimum temperature using chooses suitable material.
In an age when wedge valve is increasingly important, the researchers believe manufacturers should pay close attention to their results.
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