Rectangular steel pipes will inevitably be attached to the surface of oil during production and transportation, which will affect the quality of rust removal and phosphating, and reduce the bonding force between the coating and the substrate. Using organic solvents to dissolve saponified and unsaponified oils to remove oil stains are the main methods. Commonly used organic solvents include ethanol, gasoline for cleaning, toluene, carbon tetrachloride, trichloroethylene. Among the more effective solvents are carbon tetrachloride and trichloroethylene, which will not burn and can be used for degreasing at higher temperatures.
The factors that affect the coating of rectangular steel pipes mainly include the following four points: The passive film of rectangular steel pipes is a suppressed metastable structure in thermodynamics, and its protective effect is related to the medium in the environment. But no matter what kind of environment it is used in, it must be regularly cleaned to remove harmful substances attached to the surface.
Chloride ions are extremely harmful to the coating of rectangular steel pipes. We must strictly control the content of chloride ions in the passivation solution during the process of stopping passivation on the outside. Many passivation chemical materials have limited requirements for chloride ions. The water used for passivation solution and cleaning water also have strict water quality requirements for chloride ions to ensure that the passivation waste does not contain chloride ions.
The passivation performance of the rectangular steel pipe is low when the nickel content is low, so the martensite content and the content of chromium and nickel have a great influence on the passivation performance of the rectangular steel pipe. The more lubricated the surface of the rectangular steel tube, the lower the roughness, the more difficult it is for foreign matter to adhere, and the corrosion will be reduced to a low point. Therefore, the surface of the rectangular steel tube should be processed as much as possible. In addition, the cleaning after passivation should be stopped carefully, so that the remaining acid can promote the anode response, maintain the integrity of the film, and ensure that the appearance of corrosion resistance is strengthened.