The drainage pipe is widely used in industry for its excellent corrosion resistance, light weight and high strength, large transport flow, convenient installation, short construction period and low-level investment advantages. Good choice for irrigation, petrochemical industry. It is very convenient for water supply, low temperature resistance and stamping. These advantages are also widely used in the current industry. In different occasions, the use of drainage pipes is a very common phenomenon. More powerful effect. In the production process, the drainage pipe is heated by metal casting. When the mold is rotated, a coating or resin-coated sand is applied to the inner wall, and the coating is dull and hardened. . Because there is a layer of paint or resin-coated sand on the mold, the cooling rate of the metal liquid is greatly reduced. High-temperature annealing is not required, and only 720-760 ℃ low-temperature annealing is required.