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The national standard GB8923-2011 describes the rust removal grades as follows: ★ 【1】Spray or shot blasting for rust removal – Spray or shot blasting is indicated by the letter “Sa”. There are four rust removal grades: Sa1 for mild blasting or jetting rust removal. Without magnification, the surface should be free of visible grease and dirt, as well as any loosely attached oxides, rust, paint coatings, and other contaminants. Sa2 Thorough blast or projectile cleaning: Without magnification, the surface should be free of any visible grease and dirt; there should be almost no oxide scale, rust, coatings, or foreign impurities on it. Any residues present should be firmly adhered to the surface. Sa2.5: Very thorough spraying or blasting for rust removal. Without magnification, the surface should be free of visible oils, dirt, oxide scale, rust, coatings, and foreign contaminants; any remaining traces of contaminants should appear only as slight spot-like or strip-like discolorations. For Sa3 steel surfaces: The surface should be clean after blasting or shot blasting. Without magnification, there should be no visible oil, grease, dirt, scale, rust, coatings, or foreign impurities on the surface; the surface should exhibit a uniform metallic color. [2] Rust removal using manual and power tools: Rust removal using manual and power tools is denoted by the letters “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 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.