Connecting pipes into pipeline components. According to the connection method, it can be divided into four categories: socket fittings, threaded fittings, flange fittings, and welded fittings. It is often made of the same material as the pipe. There are elbows (elbow pipes), flanges, tees, tees (cross heads), and reducers (large and small heads), etc. Bends are used in places where pipes turn; Flanges are parts used to connect pipes to each other, connected to pipe ends, and tees are used where three pipes converge; A four-way pipe is used where four pipes converge; A reducer is used where two pipes of different diameters are connected.