The galvanizing methods of galvanized square and rectangular pipes are divided into hot-dip galvanizing and electro-galvanizing. The coating of hot-dip galvanizing is relatively uniform, has strong adhesion, and has a long service life. In this process, the chemical reaction between the steel pipe and the plating bath can make the galvanized steel pipe corrosion-resistant. However, even if it has strong corrosion resistance, rust will still occur during use.
So, what causes this? This is because the anti-rust technology of square and rectangular pipes is to use cold rolling or hot rolling to coat the outer layer of the narrow and long steel plate with a layer of zinc. The main reason why galvanized square and rectangular pipes rust is the zinc layer on the surface. Zinc has relatively active chemical properties and is soluble in acid and alkali. In a humid environment, zinc will undergo a chemical reaction and a basic zinc carbonate film will form on its surface. When it comes into contact with substances containing hydrogen sulfide, zinc's corrosion resistance decreases and it is easily corroded, and then exposed on the surface of the steel plate, so the steel pipe rusts.

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