The pipes and joint fittings made of plastic have been widely used in indoor drainage, tap water, chemical industry, wire threading pipe and other pipeline projects. Commonly used plastics include UPVC, polyethylene, polypropylene and ABS plastics (copolymer of acrylonitrile butadiene styrene). The main advantages of plastic drainage pipe are corrosion resistance and low fluid friction; Because the sundries flowing through are difficult to adhere to the pipe wall, the sewage discharge efficiency is high. The weight of plastic pipe is only 1 / 6 ~ 1 / 12 of that of cast iron pipe, which can save labor, and its price and construction cost are lower than that of cast iron pipe. The disadvantage is that the linear expansion coefficient of plastic is about 5 times larger than that of cast iron, so flexible joints need to be set on long plastic pipelines. Plastic pipes are mostly manufactured by extrusion molding, and pipe fittings are mostly manufactured by injection molding. In addition to the adhesive method, there are also hot fusion method, thread connection method, flange connection method and socket connection method with rubber sealing ring.