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There are three types of carbon steel flange sealing surface
Plane sealing surface: suitable for occasions where the pressure is not high and the medium is non-toxic;
Concave-convex sealing surface: suitable for occasions with slightly higher pressure;
Tongue and groove sealing surface: suitable for flammable, explosive, toxic media and high-pressure occasions.
A carbon steel flange gasket is a ring made of material that can undergo plastic deformation and has a certain strength. Most gaskets are cut from non-metallic plates, or manufactured by professional factories according to the specified size. It is asbestos rubber board, asbestos board, polyethylene board, etc.; there are also metal-clad gaskets made of non-metallic materials such as asbestos wrapped with thin metal plates (white iron sheet, stainless steel); there is also a thin steel strip and asbestos strip. Wrap-around gaskets wound together. General rubber gaskets are suitable for occasions where the temperature is lower than 120°C; asbestos rubber gaskets are suitable for water vapor temperatures below 450°C, oil temperatures below 350°C, and pressure When it is lower than 5MPa, acid-resistant asbestos boards are commonly used for general corrosive media. In high-pressure equipment and pipelines, lens-shaped or other-shaped metal gaskets made of copper, aluminum, No. 10 steel, and stainless steel are used. The contact width between the high-pressure gasket and the sealing surface is very narrow (line contact), and the processing finish of the sealing surface and the gasket is relatively high.
In addition, carbon steel flanges are usually coated with electroplating (yellow zinc, white zinc, etc.), or brushed with anti-rust oil or sprayed with anti-rust paint to prevent surface rust and cracks.
How to choose flanges is mainly reflected in the selection of flange connection surfaces, because there are many flange connection methods, including welding flanges, screw flanges, etc. Welding flanges have good sealing performance and can withstand repeated high temperatures and high pressure. Curved waves. Among them, the large-diameter connection of the flange is the most common. Here I will share with you the methods and specific characteristics of the large-diameter connection of the lower flange:
First of all, the large-diameter links of flanges mainly include large-diameter flat welding flanges, and large-diameter stainless steel flanges. The wear of large flanges has always been a factor affecting safe and civilized production. With the continuous development of science and technology, materials are also constantly innovating. , Cast stone, cast steel, alloy, centrifugal casting composite ceramics and other materials have appeared one after another. Among them, the pipeline is lined with alumina ceramics because of its high wear resistance, high hardness, good oxidation resistance, corrosion resistance and extremely high and low-temperature resistance. performance has become the most widely used wear-resistant material, accounting for about 80% of the international special ceramic market share (wear-resistant materials). Compared with steel pipes, the wear resistance has been improved to a certain extent, but because the reaction temperature is not high (average not exceeding 1200°C), the reaction time is short, and the reduced alumina still stays in the low-temperature phase β-Al2O3, and cannot be converted It is a high-temperature phase α-Al2O3 (change temperature exceeds 1300°C).
The large-diameter connection of general flanges has a diameter of 7M, a simple structure, convenient processing, and easy anti-corrosion. In addition, there are connections of threaded flanges. Compared with the former, this kind of connection has a better sealing effect. It must be complicated in structure, and it is difficult to replace the gasket squeezed in the groove.
The determination of the nominal pressure of the flange is related to the maximum operating pressure, operating temperature and flange data of the flange. Because when formulating the flange scale series and calculating the flange thickness, it is based on the mechanical properties of 16MnR at 200 °C. Therefore, it is stipulated that for the flange size determined on this basis, at 200°C, its maximum allowable operating pressure is considered to be the nominal pressure of the flange with this standard. For example, the so-called flange with a nominal pressure of PNO.6MPa refers to a flange with such a specific size. The flange is made of 16MnR, and its maximum allowable operating pressure is 0.6MPa at 200°C.
If this PN0.6MPa flange is used at a temperature higher than 200°C, its maximum operating pressure will be lower than its nominal pressure of 0.6MPa. Conversely, if it is used at a temperature lower than 200°C, its maximum working pressure is still determined at 200°C. If the material of the flange is changed to Q235-A, then the mechanical properties of Q235-A steel are worse than 16MnR. The flange with a nominal pressure of PN0.6MPa, even if it is operated at 200°C, its maximum allowable operating pressure will also be reduced. below its nominal pressure.
Conversely, if the material of the flange is changed from 16MnR to 15MnVR, then, because the mechanical properties of 15MnVR are better than 16MnR, the maximum allowable operating pressure of the flange with a nominal pressure of PN0.6MPa will be higher than that when operating at 200°C. its nominal pressure. In short, as long as the nominal diameter and nominal pressure of the flange are determined, the size of the flange will also be determined. As for the maximum operating pressure allowed by the flange, it depends on the operating temperature of the flange and what material it is made of.