The outer galvanized and inner plastic coated steel pipe of seamless steel pipe, like the plastic coated steel pipe, takes the steel pipe as the base pipe. The pipe is a steel pipe with internal and external coating. Generally, the inner coating is plastic for anti-corrosion. The outer coating can be about the galvanized layer of plastic according to the needs of users, or it can be another coating raw material.
Therefore, the surface pretreatment of the base pipe shall be carried out for the seamless steel pipe coated with plastic inside and galvanized outside. The detailed treatment steps are as follows:
1. Before shot peening, the seamless steel pipe shall be preheated to remove moisture, and the preheating temperature shall be 40 ℃ ~ 60 ℃;
2. Rust removal shall reach SA2 in GB / t8923 rust grades and rust removal grades of steel surfaces before coating Grade 5, the surface anchor depth of seamless steel pipe is 40 μ m～100 μ m;
3. The residual rust dust on the surface of seamless steel pipe shall be removed;
4. Spraying shall be carried out within 4h after surface pretreatment.