When galvanized products are stored or transported in humid environments, the lack of free-flowing air on the surface makes the coating susceptible to electrochemical corrosion, resulting in white or gray powdery corrosion products—commonly known as white rust. Although white rust generally does not significantly affect the coating’s corrosion resistance, prolonged exposure to a humid, enclosed environment can cause it to become severe, thereby compromising the product’s appearance and service life.

The following summarizes the causes of white rust, as well as some preventive and remedial measures.
Causes of White Rust:
Observation of products affected by white rust reveals that in areas with mild white rust, the hot-dip galvanized coating remains thick enough to protect the steel substrate, whereas in areas with severe white rust, the coating has been almost completely consumed and can no longer provide protection.
In enclosed environments, moisture, oxygen, carbon dioxide, and other oxides on the coating’s surface react chemically, producing a corrosive aqueous solution that adheres to the coating’s surface. This solution acts as an electrolyte, resulting in white, powdery rust. The severity of white rust depends on the composition of the condensed moisture and the duration of exposure to the environment.

Prevention of White Rust:
1) Place a few desiccant packets inside the packaging.
2) Use high-quality packaging for steel coils: waterproof paper + plastic film + outer packaging.

3) Maintaining a low-humidity environment and adequate ventilation around the galvanized coil can reduce white rust.

Treatment of White Rust
1) Minor white rust can be wiped off with a dry cloth after drying the steel coil in a well-ventilated area for a period of time.
2) Moderate white rust can be removed with a stiff-bristled brush (note: do not use a wire brush).
3) For severe white rust, lightly sand the area with sandpaper, then apply a specialized galvanized repair paint (a high-zinc paint containing more than 95% zinc) to restore the surface.