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During the installation and use of flanges in summer, the tightness of flanges shall be tested frequently. In the industrial field, the role of flanges is very obvious, and they are often used to seal containers. The container flange is also called the equipment flange, which is generally the flange connected with the equipment body parts; Pressure vessel flange is a kind of equipment flange with pressure bearing property. The leakage of many containers is often related to flange connection, because the failure of flange joint sealing may cause waste of energy and raw materials, or even equipment scrapping, shutdown, casualties and serious environmental pollution.
When flanges are used, they generally have matching gaskets. Gaskets are rings made of materials that can produce plastic deformation and have certain strength. Most gaskets are cut from non-metallic plates or made by professional factories according to the specified size. The materials are asbestos rubber sheets, asbestos sheets, PTFE sheets, polyethylene sheets, etc; It is also used to wrap asbestos and other non-metallic materials with a thin metal plate (galvanized iron sheet, stainless steel) to form a metal clad gasket; There is also a spiral wound gasket made of thin steel tape and asbestos tape. The commonly used spiral wound gasket is a metal spiral wound gasket made of stainless steel tape and graphite. Depending on the use environment, the spiral wound gasket can also be made of asbestos. The ordinary rubber gasket is suitable for the occasions where the temperature is lower than 120 ℃; Asbestos rubber gasket is applicable to the occasions where the water vapor temperature is lower than 450 ℃, the oil temperature is lower than 350 ℃, and the pressure is lower than 5MPa. For general corrosive media, acid resistant asbestos board is commonly used.
Common pressure vessel flange standards: 1157-82 ～ 1160-82, 4700-2000 ～ 4707-2000 B16.47A/B B16.39 B16.48
High pressure vessel flange is used for A-type flat welding flange of steel pressure vessel with nominal pressure of 0.25-1.6MPa and working temperature higher than - 20 ℃~300 ℃
Therefore, in the industrial field, the flange connection should be checked regularly, and soap bubbles were found near the flange weld. The flange with leakage is a raised face neck flat welding steel pipe flange, which is made of 304. Its contact medium is gaseous vinyl chloride monomer (VCM) and clean water. The design pressure is 1.4MPa, the working pressure is 1.1MPa, the reaction temperature is 64.7 ℃, and the temperature range is 30-70 ℃.
In addition, there are many reasons for flange leakage, and it is necessary to carry out reasonable inspection, including macro morphology analysis. Macroscopic observation shows that there are visible cracks on the outer wall of the flange, and the cracks are concentrated near the weld zone. The crack distribution and crack shape are shown.
