It is very important to correctly select the coating type in the construction of surface treatment, which is related to the service life of the protective effect of the coating on the steel structure. However, after the coating varieties are determined, it is more important to determine whether the surface treatment and construction process of steel plate meet the respective requirements of different coating varieties. Because any paint can not exert the best effect on the poorly treated surface. Paint on the surface contaminated by rust, oil stain and other impurities, and any paint will fail in a short time. In order to ensure the best protective performance of the heavy-duty anti-corrosion coating used, the surface treatment of the steel plate is extremely important and cannot be neglected.

1. The pretreatment of steel surface shall remove the impurities attached to the surface of steel plate, and the grease and other dirt shall be removed with diluent or cleaning agent. If there are sulfates or corrosive salts, wash them with clean water and dry them with compressed air. On the steel pretreatment pipeline, the oxide scale, rust and other impurities shall be removed by shot blasting or sand blasting, and then the steel surface shall be cleaned by vacuum cleaner or purified compressed air. After the derusting quality of the pretreated steel meets the requirements, a layer of shop primer must be applied immediately to prevent the steel from rusting during storage, assembly and coating, and the surface of the steel plate shall be protected by the anti-rust paint after coating. The rust removal quality of the steel after shot blasting or sand blasting shall at least reach Sa2.5. When sectional shot blasting or sand blasting is used for derusting, the first coat of antirust paint can be directly applied after the derusting quality of the whole section meets the requirements, without the need for shop primer.

2. For the surface treatment of steel plate coated with shop primer (i.e. secondary rust removal), the water, moisture, grease, rust, zinc salt, marks and other dirt drawn with chalk or paint on the shop primer surface shall be cleaned with clean water and then wiped with solvent. If the paint film of the workshop primer is damaged and rusted during storage, transportation, operation, rolling, cutting, welding, etc., the damaged and rusted parts shall be cleaned with pneumatic steel wire or disc grinding wheel grinder, etc. After meeting the requirements of derusting quality, the first layer of anti-rust paint can be applied.

3. Standards and requirements for surface treatment In order to control the derusting quality of steel plate surface and meet the requirements of different types of coatings, many countries have formulated derusting standards for steel and other metal materials. At present, the most widely used standard in the world is the "Schematic Surface Preparation Standard for Painting Steel Surface" (SIS55900-1967) published by the Swedish Corrosion Institute. China issued its equivalent national standard GBB8923-88 Rust Grades and Derusting Grades of Steel Surfaces before Painting in 1988. The derusting grade of different shop primers or heavy-duty anti-corrosion coatings is required in the product specification. The surface of shot blasting or sand blasting derusting steel has formed a certain roughness, which can improve the adhesion of the paint film. Generally, the maximum roughness is not expected to exceed 100 μ m. If the roughness is too large, not only too much paint will be consumed, but also bubbles may remain on the cross section of the paint film, or wave peaks that are not covered by the paint film may occur. The size of surface roughness depends on such factors as abrasive particle size, shape, material and spray speed. The particle size of abrasive has a great influence on the roughness. To make the maximum roughness not more than 100 μ m. The average grain size of abrasive used for shot blasting or sand blasting shall not exceed 1mm. Surface roughness can be measured or compared with stylus profiler and standard sample block.