Flanges, also known as raised face plates or flanged disks, are components used for connecting shafts to shafts, typically for pipe end connections. They are also used at equipment inlets and outlets, such as on reducers. A flange connection or flange joint refers to a removable connection made up of the flange, gasket, and bolts, forming a combined sealing structure. Pipe flanges are flanges used in piping installations, while equipment flanges refer to the inlets and outlets of equipment. Flanges have holes for bolts, which secure the two flanges together, and are sealed with a gasket. Flanges are available in threaded (screwed) connections, welded flanges, and clamping flanges. Flanges are used in pairs; low-pressure piping can use threaded flanges, while pressures above four kilograms require welded flanges. Two flange disks are joined with a sealing gasket and then bolted together. Flange thickness varies with pressure, as do the bolts used. In pumps and valves, the parts that connect to pipes are also shaped like flanges and are called flange connections. Any connection piece that uses bolts to connect two flat surfaces and seal them is generally called a "flange," such as in ventilation pipe connections. Such components can be referred to as "flange-type parts." However, this type of connection is only a part of a single device, like the connection between a flange and a pump, so it's not appropriate to call the pump a "flange-type part." Smaller components like valves can be called "flange-type parts."

Flange connections involve securing two pipes, fittings, or equipment to separate flange plates first, then inserting a flange gasket between them and fastening them together with bolts, completing the connection. Some fittings and equipment come with flange plates as standard, which also fall under flange connections. Flange connections are a crucial method in pipeline construction. They are convenient to use and can withstand high pressure. In industrial pipelines and residential settings, where pipe diameters are small and the pressure is low, flange connections are not visible. However, in boiler rooms or production sites, you will find flange-connected pipes and equipment everywhere.

According to the type of connection, flange connections can be categorized as: flat welding flange, socket welding flange, blind flange, threaded flange, bolted flange, ring-type joint flange, loose flange with socket welding ring, loose flange with flat welding ring, ring groove face flange, and flange cover, large diameter flat flange, large diameter high neck flange, winged blind flange, and socket welding ring loose flange, etc.