The pipe fitting is a component that connects the pipe into a pipe. According to the coupling method, it can be divided into four types: socket pipe fitting, threaded pipe fitting ,fanged pipe fitting and welded pipe fitting.The elbow is used for the pipe to tun; the flange is used to make the pipe The parts connected to the pipe are connected to the pipe end, the tee pipe is used for the place where the three pipes are collected,the four-way pipe(cross pipe) is used for the place where the four pipes are collected, and the reducer pipe is used for the connection of the two pipes of different pipe diameters.