Manufacturing and installation requirements for low-temperature valves

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Due to the special structure of low-temperature valves, their installation also has specific requirements. Due to the structural characteristics of the long-neck valve cover in low-temperature valves, during installation the stem of such valves must be at an angle of 45 degrees relative to the vertical upward direction, and it is advisable to avoid installing them on vertical pipelines. Otherwise, the low-temperature medium will fill the extended portion of the valve cover, causing the valve packing to fail, and it will also transfer cold heat to the valve handle, posing a risk of injury to the operator. For low-temperature valves equipped with pressure relief mechanisms, special attention must be paid to the requirements regarding the direction of pressure release when installing the valve. The direction of pressure release from the valve should be indicated on the process flow diagram and reflected in the piping axonometric view (this is extremely important, extremely important, extremely important). If pressure relief holes are necessary but not provided, the liquid inside the valve chamber will vaporize when heated, which can very easily cause the valve body to explode. If the direction of pressure release is incorrect, flammable or toxic process media may be released toward the operation and maintenance side, resulting in casualties! The manufacturing of low-temperature valves involves strict manufacturing processes and the use of specialized equipment, with rigorous quality control over the processing of components. Through a special low-temperature treatment, the roughly machined parts are placed in a cooling medium for several hours (2–6 hours) to relieve stresses, ensure the material’s performance at low temperatures, and maintain precise dimensions. This prevents leakage caused by deformation due to temperature changes when the valve is operating in low-temperature conditions. The assembly of valves also differs from that of ordinary valves; the components must be thoroughly cleaned to remove any oil residues in order to ensure optimal performance. Inspection of low-temperature valves: In addition to normal-temperature and low-temperature tests, the following inspections should also be carried out for low-temperature valves: 1. All major components of ultra-low-temperature valves must undergo cryogenic treatment. 2. The main components as well as the welds must be tested for low-temperature impact resistance to ensure that the valves do not crack under low-temperature conditions. 3. The valves must undergo normal-temperature tests, first with a hydrostatic pressure test at 1.5 times the nominal pressure, followed by a sealing test at 1.1 times the nominal pressure. 4. After the hydrostatic test, any moisture from the valves must be removed, and there should be no grease present; the valves must remain dry. 5. A certain proportion of valves in each batch must be sampled for low-temperature testing, and this testing must be conducted after the hydrostatic pressure test at 1.5 times the nominal pressure. 6. After the low-temperature testing, it is necessary to prevent air from entering the valves ； 7. After the low-temperature test of the valve, it should be allowed to warm up naturally or blown with a fan; it is strictly prohibited to use heating or other methods to accelerate the warming up of the valve ； 8. After the natural temperature rise during the low-temperature test of the valve, tighten the valve fasteners again ； 9. When valves are stored in inventory, it is essential to check their opening and closing functions to ensure they are in proper condition. 10. During storage and transportation, stainless steel valves should be kept separate from carbon steel valves, and measures should be taken to protect them from dust, water, oil, and physical damage. 11. The flow direction of the valves, the direction of pressure release, and the information on the nameplates must all be checked in accordance with the requirements of the design team.