How is the rusting grade of steel surfaces determined? How is the processing level determined?

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The rusting grade is determined in accordance with GB/T 8923-1. The rusting degree on the surface of steel is divided into four grades: A. A steel surface that is completely covered with scale with almost no rust; B. A steel surface that has developed rust and some of the scale has fallen off; C. A steel surface whose scale has peeled off due to rusting or can be scraped off, with minor pitting; D. A steel surface whose scale has completely peeled off due to rusting, with widespread pitting. There are three methods for removing rust from the surface of grade-treated steel, denoted by the letters Sa, St, or SI. 1. Jet or blast rust removal sa, with a total of four grades. Grade Sa1: It involves simple manual brushing and sanding with sandpaper; it is the grade with the lowest level of cleanliness among the four, and its protection for the coating is only slightly better than that of parts that have not undergone any treatment. Technical standards for Sa1 level treatment: The surface of the workpiece must be free from any visible contaminants such as oil, grease, residual scale, rust spots, and leftover paint. Sa1 grade is also known as the manual brushing cleaning grade. (Sweeping grade) Sa2 grade: This grade is achieved using sandblasting as the cleaning method; it represents the lowest level of sandblasting treatment and meets the basic requirements. However, it provides much better protection for the coating compared to cleaning by hand brushing. Technical standards for Sa2 level treatment: The surface of the workpiece must be free from visible grease, dirt, oxide scale, rust, paint, oxides, corrosion products, and other foreign substances (except for defects). Defects are allowed at a rate of no more than 33% per square meter of surface area; slight shadows are permitted, as well as minor discoloration caused by defects or rust, along with oxide scale and paint-related defects. If the original surface of the workpiece has indentations, slight rust and paint will also remain at the bottom of those indentations. Grade Sa2 is also known as the commercial cleaning grade (or industrial grade). Grade Sa2.5: It is a grade that is widely used in industry and can serve as the technical requirements and standards for acceptance. Grade Sa2.5 is also known as the near-white cleaning grade (near-white grade or white-ready grade). Technical standards for Sa2.5 treatment: The same as the first half of the Sa2 requirements, but defects are limited to no more than 5% per square meter of surface area; slight shadows are allowed; minor discoloration caused by defects or rust is permissible; as well as oxide scale and paint defects. Grade Sa3: It is the highest treatment grade in industry, also known as the white cleaning grade (or white grade). Technical standards for Sa3 treatment: The same as those for Sa2.5, but 5% of shadows, defects, rust, etc. are not allowed to be present. Regarding the spraying treatment of steel surfaces, we just need to remember that the Sa sandblasting grade is required to increase gradually from 1 to 3. The commonly used sandblasting grade is Sa2.5. 2. Cleaning with manual and power tools: Before cleaning with manual or power tools, all layers of thick rust must be removed. Visible oil, grease, and dirt should also be removed. After cleaning with manual and power tools, the loose dust and debris on the surface should be removed. St2: Thorough cleaning using manual and power tools. When observed without magnification, the surface should be free of visible oil, grease, and dirt, as well as any loosely attached scale, rust, coatings, or foreign contaminants. St3: Very thorough cleaning using manual and power tools. Same as St2, but the surface treatment must be much more thorough; the surface should have the luster of a metal substrate. 3. Flame cleaning: F1 is used less frequently, so no description is provided.