Shajiabang galvanized steel pipe coated with steel pipe as the base, both inside and outside the coated steel pipe for the plastic pipe. The inner coating is plastic, used to prevent corrosion, the outer coating can be plastic, zinc coating or other coating materials as needed. Base pipe can be welded steel pipe, seamless steel pipe or galvanized steel pipe. The earliest coated steel tube base pipe is galvanized steel pipe, and later found that the inner wall galvanized to improve the adhesion of the inner coating is not good, but have an impact, while increasing the cost of galvanizing process, in order to improve the adhesion of the inner coating , Galvanized steel pipe galvanized within the zinc but also to take the process, which once again increased costs, but also resulted in a waste of energy. Therefore, there are also welded steel pipe directly coated. As a result, the base pipe there are three: 1, galvanized steel pipe inside and outside the wall of hot-dip galvanized, but the processing of plastic coated steel pipe, galvanized zinc to go through the coating process better, of course, there are not taken Zinc technology, in the galvanized layer and then coated with plastic. 2, the inner and outer wall galvanized welded steel pipe. 3, the outer wall galvanized, the inner wall is not galvanized steel, but the market price of steel than galvanized galvanized steel pipe wall is also more expensive, so in fact less used. Base pipe before the plastic coating should be used sandblasting or acid phosphating and other processes to remove the metal surface rust, oil and zinc coating, commonly known as surface pretreatment. The construction industry on the surface of non-quantitative indicators of pre-treatment requirements, the oil industry is relatively specific, as provided: 1, before the shot peening, steel pipe should be preheated to get rid of moisture, preheating temperature of 40 ℃ ~ 60 ℃; 2, Should reach GB / T8923 "coating steel surface rust grade and derusting grade" in Sa2.5 grade, steel pipe surface anchor depth of 40μm ~ 100μm; 3, the steel surface residual rust and dust should be removed; 4, the surface of the pre- 4h after treatment should be sprayed; ...... and so on. Surface pretreatment is a concealed project, once the coating is covered, the rust is completely, it is difficult to check the cleanliness, and the surface pretreatment is to spend money, so some companies ignore the surface pretreatment in order to save money, But the final effect will be reflected in the product, the surface pretreatment well, the coating is solid, the surface pretreatment so-so, the coating will fall off. However, China requires that complaints be passed within two years, so some companies are making coatings that do not fall off within two years. In this regard, we believe that we should establish a brand awareness, encourage the construction, recommend quality products, eliminate two-year-old products. The main coating for corrosion protection is mainly epoxy resin and polyethylene two different nature of the two materials, a thermosetting plastic, a thermoplastic. Coating Thickness Normal polyethylene coating (PE coating) is thicker than epoxy coating (EP coating). Epoxy coating brittle, so do flattening test, EP coating is only pressed to 4/5 of the diameter, and PE coating to pressure to 2/3 diameter. The inner coating of domestic drinking water is usually made of polyethylene.