The parts that connect pipes to each other are connected to the ends of the pipes. There are holes on the flange, and bolts tightly connect the two flanges. Seal the flanges with gaskets. Flanged pipe fittings refer to fittings with flanges (flanges or flanges). It can be made by casting (not shown in the picture), or by threaded connection or welding. A flange joint consists of a pair of flanges, a gasket, and several bolts and nuts. The gasket is placed between the two flange sealing surfaces. After tightening the nut, the pressure on the gasket surface reaches a certain value and deforms, filling the uneven areas on the sealing surface to ensure a tight and leak free connection. Flange connection is a detachable connection. According to the connected components, it can be divided into container flanges and pipe flanges. According to structural types, there are integral flanges, loose flanges, and threaded flanges. Common integral flanges include flat welding flanges and butt welding flanges. Flat welding flanges have poor rigidity and are suitable for situations with pressure p ≤ 4MPa; Welding flanges, also known as high neck flanges, have high rigidity and are suitable for applications with high pressure and temperature. There are three types of flange sealing surfaces: flat sealing surfaces, suitable for situations with low pressure and non-toxic media; Concave convex sealing surface, suitable for situations with slightly higher pressure; Mortise and tenon sealing surface, suitable for flammable, explosive, toxic media and high-pressure environments. A gasket is a circular ring made of a material that can undergo plastic deformation and has a certain strength. Most gaskets are cut from non-metallic plates or made by professional factories according to specified sizes, and their materials include asbestos rubber sheets, asbestos sheets, polyethylene sheets, etc; Metal gaskets made by wrapping non-metallic materials such as asbestos with thin metal plates (such as white iron sheet and stainless steel) are also used; There is also a wrapped gasket made by winding thin steel strips and asbestos strips together. Ordinary rubber gaskets are suitable for situations where the temperature is below 120 ℃; Asbestos rubber gasket is suitable for situations where the temperature of water vapor is below 450 ℃, the temperature of oil is below 350 ℃, and the pressure is below 5MPa. For general corrosive media, acid resistant asbestos board is the most commonly used. In high-voltage equipment and pipelines, lens shaped or other shaped metal gaskets made of copper, aluminum, No. 10 steel, stainless steel are used. The contact width between the high-pressure gasket and the sealing surface is very narrow (line contact), and the machining smoothness of the sealing surface and gasket is high.
Flanges are divided into threaded connection (threaded connection) flanges, welded flanges, and sleeve flanges. Low pressure small diameter flanges have threaded flanges and sleeve flanges, while high pressure and low pressure large diameter flanges use welded flanges. The thickness of flange plates and the diameter and quantity of connecting bolts vary for different pressures.