A flange, also called a flange plate or flanged plate, is a component used to connect pipes to each other, attached to the pipe ends. Flanges have holes, and bolts are used to tightly connect two flanges. A gasket is used for sealing between flanges. Flanged pipe fittings refer to pipe fittings with flanges (flanges or flanged plates). They can be cast (image unavailable), threaded, or welded. A flange joint consists of a pair of flanges, a gasket, and several bolts and nuts. The gasket is placed between the sealing surfaces of the two flanges. After tightening the nuts, the specific pressure on the gasket surface reaches a certain value, causing deformation and filling the unevenness of the sealing surfaces, making the connection tight and leak-proof. A flange connection is a detachable connection. According to the connected components, they can be divided into vessel flanges and pipe flanges. According to the structural type, there are integral flanges, slip-on flanges, and threaded flanges. Common integral flanges include slip-on flanges and weld neck flanges. Slip-on flanges have relatively poor rigidity and are suitable for applications with pressure p ≤ 4MPa; butt-welded flanges, also known as high-neck flanges, have greater rigidity and are suitable for applications with higher pressure and temperature. There are three types of flange sealing surfaces: flat sealing surface, suitable for low-pressure and non-toxic media; raised face sealing surface, suitable for slightly higher pressure applications; and tongue and groove sealing surface, suitable for flammable, explosive, toxic media and high-pressure applications. A gasket is a ring made of a material capable of plastic deformation and possessing a certain strength. Most gaskets are cut from non-metallic sheets or manufactured to specified dimensions by specialized factories, using materials such as asbestos rubber sheets, asbestos sheets, and polyethylene sheets; there are also metal-clad gaskets made by wrapping non-metallic materials such as asbestos with thin metal sheets (galvanized iron, stainless steel); and there are also spiral wound gaskets made by winding thin steel strips and asbestos strips together. Ordinary rubber gaskets are suitable for temperatures below 120℃; asbestos rubber gaskets are suitable for water vapor temperatures below 450℃, oil temperatures below 350℃, and pressures below 5MPa. For general corrosive media, acid-resistant asbestos boards are most commonly used. In high-pressure equipment and pipelines, lens-type or other shaped metal gaskets made of copper, aluminum, No. 10 steel, or stainless steel are used. High-pressure gaskets have a very narrow contact width with the sealing surface (line contact), and the surface finish of both the sealing surface and the gasket is high.
Flanges are classified as threaded flanges, welded flanges, and compression fitting flanges. Low-pressure, small-diameter flanges use threaded flanges and compression fitting flanges, while high-pressure and low-pressure, large-diameter flanges use welded flanges. The thickness of the flange and the diameter and number of connecting bolts differ depending on the pressure.
