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How to manufacture and inspect cryogenic valves

Update:15-04-2021
Summary:

Because of the special structure of the cryogenic valve […]

Because of the special structure of the cryogenic valve, the installation of the cryogenic valve also has its special requirements. Because of the structural characteristics of the long-neck bonnet of the cryogenic valve, the direction of the stem of the cryogenic valve must be within a vertical angle of 45 degrees during installation, and installation on vertical pipelines should be avoided as much as possible. Otherwise, the low temperature medium will fill the extended part of the valve cover, causing the valve packing to fail, and will transfer the cold to the valve handle, causing personal injury to the operator.

For cryogenic valves with pressure relief structure, when installing the valve, pay special attention to the requirements of the valve pressure relief direction. The direction of valve pressure relief should be marked on the process flow chart and reflected in the pipeline isometric drawing (this point is extremely important, extremely important, and extremely important). If it is necessary to set a pressure relief hole and not set it, after the valve is closed, The liquid in the valve cavity is heated and vaporized, which can easily cause the valve body to burst. If the pressure relief direction is installed in the wrong direction, the flammable or toxic process medium may be leaked to the operation and maintenance side, causing casualties!

Cryogenic valve manufacturing

Strict manufacturing technology and special equipment are adopted for the produced cryogenic valves, and strict quality control is carried out on the processing of parts. After a special low-temperature treatment, the rough-machined parts are placed in the cooling medium for several hours (2-6 hours) to relieve stress, ensure the low-temperature performance of the material, and ensure the finished size to prevent the valve from being in low-temperature conditions. Leakage caused by deformation caused by temperature changes. The assembly of the valve is also different from that of the ordinary valve. The parts need to be strictly cleaned to remove any oil stains to ensure the performance.

Cryogenic valve inspection

In addition to normal temperature and low temperature tests, cryogenic valves should also be inspected as follows:

1. The main parts of the ultra-low temperature valve should be cryogenically treated (how to cryogenically treated later, we have the opportunity to talk about it, the following figure is the cryogenic treatment of the valve);

2. The main parts and welds should be subjected to low temperature impact test to ensure that the valve is not brittle under low temperature conditions;

3. The valve must be tested at room temperature, firstly with 1.5 times the nominal pressure hydraulic strength test, and then 1.1 times the nominal pressure sealing test;

4. After the water pressure test, the valve must be cleaned of water, no grease, and kept dry;

5. Each batch of cryogenic valves should be sampled for low temperature test according to a certain proportion, and the low temperature test must be carried out after 1.5 times the hydraulic strength test;

6. After the valve low temperature test, prevent air from entering the valve;

7. After the low temperature test of the valve, it should be heated naturally or blown by a fan. It is strictly forbidden to use heating and other methods to accelerate the temperature of the valve;

8. After the valve low temperature test naturally heats up, tighten the valve fasteners again;

9. When the valve is put into storage, the valve switch must be checked to ensure that the valve is in a reasonable state;

10. In the process of valve storage and transportation, attention should be paid to the separation of stainless steel and carbon steel valves, and to prevent dust, water, oil and bumps;

11. The flow direction, pressure relief direction and nameplate of the valve should be checked in accordance with the requirements of the design unit.

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