What should be done for surface corrosion of rigid waterproof casing?

What should be done for surface corrosion of rigid waterproof casing?
Rigid waterproof casing consists of steel pipe and outer wing ring, which is installed in the wall (mainly concrete wall) and used to pass through hundreds of pipes in the wall, which is conducive to the waterproofing of the wall. However, rigid waterproof casing is only considered for pipes passing through walls. What should be done to preserve the surface of rigid waterproof casing?
 
The easy way is to use a solvent for manual cleaning. The emulsion is used to clean the steel surface to remove oil, grease, dust and other organic matter from the steel surface, but the method does not remove rust and other stains from the steel surface. Steel surfaces can be polished with wire brushes and other tools to remove loose or warped oxide, rust, weld slag and other stains. Pickling also removes oxidation, rust and old coatings and can sometimes be used as a re-treatment after sandblasting. However, pickling pollutes the environment and causes great harm to humans. As a rule, pickling is not recommended for rigid waterproofing sleeves. A good method is to perform spray descaling. Spray descaling is to make a high-speed version of the jet blade driven by a high-powered motor rotate, which not only completely removes rust, oxides and dirt, but also achieves the desired uniform roughness under strong abrasive and frictional action.