Ductile iron pipes for water supply and drainage are made of gray cast iron. Because ductile iron pipes for water supply need to bear pressure, gray cast iron pipes of HPT 200 and HT 250 are usually used, and gray cast iron pipes for drainage generally use HT 150 or less. Ductile iron pipes for water supply are all centrifugal casting, and the appearance of iron pipes is smooth. If it is a socket-type ductile iron pipe, the socket is deep, the pipe wall is thick, and the length of a single pipe is 6m. Some drainage ductile iron pipes are cast by vertical formwork or small centrifugal casting machine. The appearance of iron pipe is rough, the length of single pipe is 3m, the socket is shallow and the pipe wall is thin. Before leaving the factory, the water pressure test must be carried out according to the specifications, and the factory can only leave after passing the test. Ductile iron pipes for drainage are only qualified in appearance inspection, tapping and listening inspection, and there are no air holes, cracks and broken sounds. These are introduced in official website, Guanghua and Liaocheng, and the popular science is very detailed, so you can learn about it.