Derusting grade of seamless steel pipe

The fundamental point of the surface treatment standard is four different rust levels:
The surface of Grade A steel is completely covered with adhering oxide scale, and there is almost no rust.
The surface of grade B steel has begun to rust, and the oxide scale has begun to peel off in flakes.
The oxide scale on the surface of grade c steel has been rusted or can be scraped off, but slight rust spots can be seen with the naked eye.
The oxide scale on the surface of D grade steel has been rusted and peeled off, and a large number of rust spots can be seen with the naked eye.
According to SISO55900, the surface treatment of these corrosion grades is performed by wire brush rust removal and sandblasting according to the following quality standards:
St-wire brush derusting standard St2, St3
Sa-sand blasting standard Sa1, Sa2, Sa2.5, Sa3 wire brush rust removal-St St2 thorough manual and power tool rust removal
The surface should be free of visible grease, dirt, oxide scale, rust, paint coating, and impurities.
St3 very thorough manual and power tool rust removal
Same as St2, but should be processed more thoroughly than St2, and the metal substrate is metallic luster.
These standards provide great guidance and assistance for surface treatment. Paint suppliers generally stipulate corresponding surface treatment standards and requirements for each type of paint.
Sandblasting and derusting-sa All thick rust layers on the surface should be removed before sandblasting and rust removal and visible oil, grease, and dirt should also be removed. The surface should be clean after sandblasting and rust removal, free of dust and debris.
Sa1 grade mild sandblasting
The surface should be free of visible grease, dirt, weakly attached scale, rust, paint coating, and impurities.
Sa2 grade thorough sandblasting and derusting surface should be free of visible grease, dirt, oxide scale, rust, paint coating, and impurities, and the residue should be firmly attached.
Sa2.5 grade very thorough sandblasting and rust removal surface should be free of visible grease, dirt, oxide scale, rust, paint coating, and impurities, and the residue traces only show slight spots or streaks.
Sa3 grade sandblasting and derusting to the clean surface of the steel surface should be free of visible grease, dirt, oxide scale, rust, paint coating, and impurities, and the surface has a uniform metallic color.