Generally, galvanized pipes do not need to be painted. If they are painted, they are usually painted with silver paint. After the steel pipe is galvanized, the surface is covered with a layer of zinc coating, which isolates the steel pipe from the atmosphere, avoids direct contact and corrosion of the steel pipe by the atmosphere, and is protected. As for the zinc coating on the surface of the steel pipe, due to the relatively strong chemical activity of zinc, a thin and dense layer of zinc carbonate will be formed in the air at room temperature to protect the zinc itself from further oxidation.
Therefore, galvanized pipes, both the surface zinc and the steel pipe itself, are protected from rust and do not need to be painted with anti-rust paint. Only when the galvanized layer is damaged (such as steel pipe welding and the coating at the joint is burned) and the steel pipe is exposed to the air and loses the protection of the galvanized layer, is it necessary to reapply anti-rust paint.
The substrates (anti-rust primers) suitable for galvanized parts include epoxy zinc yellow primer (two-component) and epoxy ester zinc yellow primer. Galvanized parts are non-ferrous metals, and non-ferrous metals have poorer adhesion than black all-metal. Commonly used alkyd iron red primers and epoxy iron red primers on the market are not suitable for use on galvanized parts, otherwise they will easily fall off. It should be pointed out in particular that when alkyd paint is used on galvanized parts, a saponification reaction will occur. Not only will the coating fail, but the original galvanized layer will also be damaged.
Pre-treatment when painting galvanized parts:
1. If possible, you can phosphate the galvanized parts, or spray a thin layer of phosphating primer first.
2. Or sand-sweep the surface of smooth galvanized parts.
3. Wipe the surface of galvanized workpieces and galvanized pipes with solvent (i.e. epoxy zinc yellow primer diluent) to remove the protective layer of crude oil on the workpiece and increase cleanliness.
4. Two-component epoxy zinc yellow primer: Prepare the paint strictly according to the ratio of paint and curing agent, and after curing for 30 minutes, adjust the appropriate construction viscosity before spraying. One-component epoxy ester zinc yellow primer: adjust the appropriate construction viscosity and apply it with the correct construction method.