Causes and prevention measures of white rust on galvanized steel sheets: protection guide during storage and transportation
release time：
2025-09-19 16:42
White rust on galvanized steel sheets is a common corrosion problem during storage and transportation. Its causes and preventive measures can be summarized as follows:
I. Causes of White Rust
Electrochemical Corrosion Mechanism
When galvanized steel sheets are stacked closely together in a humid environment, an oxygen concentration cell forms between the coatings, causing rapid corrosion of the zinc layer, forming a loose film of zinc hydroxide (Zn(OH)₂) and zinc oxide (ZnO) rather than a dense protective film of basic zinc carbonate (ZnCO₃).
Environmental Factors
High humidity, condensation, or direct contact with water (such as rain) accelerates the formation of white rust.
Poorly ventilated storage environments hinder the formation of a protective film.
Process Defects
Incomplete passivation or insufficient drying can lead to residual moisture on the zinc coating surface or render the passivation solution ineffective.
II. Preventative Measures
(I) Warehouse Management
Environmental Control
Select a well-ventilated warehouse located on elevated ground, and use dehumidification equipment if necessary. Avoid direct contact with wet surfaces. It is recommended to store on elevated surfaces (e.g., using wooden strips).
Stacking Specifications
Maintain space between galvanized sheets to avoid close stacking.
Follow the "first-in, first-out" principle to shorten storage cycles.
(II) Transportation Protection
Moisture-Proof Measures
Cover with waterproof tarpaulin to avoid exposure to rain or seawater.
Special sealing and moisture-proofing are required during shipping.
Shock Absorption
Use rubber pads for cushioning and securing the coils to reduce friction and vibration.
(III) Process Optimization
When ordering, select post-treatments such as chromic acid treatment and oiling to enhance corrosion resistance.
Ensure the passivation solution is effective and thoroughly dried.
III. White Rust Treatment Methods
Minor White Rust: After unpacking and drying, wipe with oxalic acid and rinse with clean water.
Severe White Rust: Remove the corrosion layer, spray with hot-dip galvanizing spray paint, and re-passivate.
The above measures can effectively reduce the risk of white rust and ensure the anti-corrosion performance and appearance quality of galvanized sheets.
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