Material Selection
1.Valve body, valve cover and other pressure resistant parts:
Usually, toughness materials with good low-temperature strength are used, such as austenitic stainless steel (such as 304L, 316L, etc.), nickel based alloys (such as Inconel 625, Hastelloy, etc.), and aluminum alloys (such as Al-6061). These materials have good low-temperature toughness and corrosion resistance, and can maintain their strength and ductility in low-temperature environments.
The most commonly used low temperature levels in engineering company design are -46 ℃, -101 ℃, and -196 ℃- Low temperature grades of 46 ℃ generally use low-temperature carbon steel, while low-temperature grades of -101 ℃ and -196 ℃ generally use 300 series austenitic stainless steel.
2.Sealing material:
Common sealing materials include polytetrafluoroethylene (PTFE), polyetheretherketone (PEEK), etc. These materials can still maintain good elasticity and sealing performance at low temperatures, ensuring the sealing reliability of valves in extremely low temperature environments.
Sealing Technology
1.Sealing surface overlay with cobalt based hard alloy:
Hard alloy has small deformation and wear resistance at low temperatures, and can maintain good sealing performance. This technology is widely used in the sealing surface treatment of low-temperature valves to ensure that the valve can maintain a tight sealing effect after long-term operation.
2.Flexible graphite or polytetrafluoroethylene composite packing:
Low temperature valves typically use flexible graphite or polytetrafluoroethylene composite packing structures, which have good low-temperature resistance and can maintain their elasticity and sealing performance at extremely low temperatures. Meanwhile, the combined packing structure can also improve the wear resistance and service life of the packing.
Structural Design
1.Long neck valve cover structure:
A significant feature of low-temperature valves is that their valve covers are usually of a long neck structure. This design is mainly aimed at keeping the valve operating handle and packing box structure away from low temperature areas, avoiding operator frostbite caused by too low temperature, while ensuring that the packing box and pressure sleeve are used at normal temperature, preventing the sealing performance of the packing from being reduced, and extending the service life of the packing. In addition, the long neck valve cover is also convenient for cold insulation construction and for tightening the gland bolts or adding packing at any time.
2.Drip board structure:
To avoid or reduce the transmission of medium temperature to the valve stem and its upper filling material, and prevent these materials from failing due to freezing, a drip plate structure can be added to the valve. The drip board can prevent low-temperature liquefied water vapor from dripping onto the flange bolts, avoiding bolt corrosion and affecting online maintenance. At the same time, the drip board is set outside the insulation layer to prevent condensed water droplets from falling onto the insulation layer and the upper part of the valve body, protecting the insulation layer and preventing the loss of cooling capacity.
3.Pressure relief structure design:
For low-temperature valves with closed cavity structures, special consideration should be given to the design of pressure relief structures when applied to flammable, explosive, and easily vaporized media. This design can achieve automatic relief in case of overpressure inside the valve, ensuring the safety of the valve and the factory. For example, low-temperature gate valves, ball valves, etc. may have significant differences in pressure relief design due to different sealing principles.
4.Anti static and fireproof structural design:
Due to the fact that low-temperature valves are generally used in flammable and explosive media, anti-static and fire-resistant designs are particularly important. Anti static design usually uses a current guiding method similar to a lightning rod to connect the valve stem and valve body, thereby exporting static electricity to eliminate safety hazards. The design of fire-resistant structures is mainly aimed at addressing the issue of medium leakage caused by drastic temperature changes.
