Steel surface treatment rust removal grades
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Rust removal grade: Refers to the level of cleanliness achieved in surface treatment. Standards for steel surface treatment ★ The national standard GB8923-2011 provides descriptions of rust removal grades. ★ [1] Jet or blast rust removal: Jet or blast rust removal is indicated by the letter “Sa”. There are four rust removal grades: Sa1 for mild blasting or jetting removal. Without magnification, the surface should be free of visible grease and dirt, as well as any loosely attached oxidized scale, rust, paint coatings, or other contaminants. Sa2: Complete blasting or jetting for rust removal. Without magnification, the surface should be free of visible grease and dirt, and there should be almost no scale, rust, coatings, or foreign contaminants; any remaining residues should be firmly attached to the surface. Sa2.5: Very thorough jet or blast cleaning. Without magnification, the surface should be free of visible oils, dirt, scale, rust, coatings, and foreign contaminants; any remaining traces of such contaminants should appear only as slight spot-like or streaky discolorations. For Sa3 steel, spray or shot blasting is used for rust removal, ensuring that the surface is free from visible oils, greases, dirt, scale, rust, coatings, and foreign contaminants when viewed without magnification. The surface should have a uniform metallic color. 【2】Rust removal with manual and power tools – Rust removal using manual and power tools is indicated by the letter “St”. There are two rust removal grades: St2, which requires thorough rust removal by hand and power tools; without magnification, the surface should be free of visible oil, grease, and dirt, as well as any loosely attached oxide scale, rust, coatings, or foreign contaminants. St3 is the same as St2, but more thorough; the surface should have the luster of the base metal. 【3】Flame cleaning: Without magnification, the surface should be free of visible oil, grease, dirt, scale, rust, coatings, and foreign contaminants; any remaining traces should be limited to surface discoloration.
The corrosion grade ranges from 1 to 4, with grade 1 being the highest level; it requires a high degree of surface cleanliness with few rust spots； Level 2 results in an average surface cleanliness level; however, large areas of rust are not allowed, and even small areas of rust cannot be too severe ； Grade 3 cleanliness is lower than Grade 2; there are slight rust marks on the surface, but no large areas of rust ； Grade 4 is the lowest grade; there are slight rust spots on the surface, but there should not be many large areas of rust.