Storage Precautions for Galvanized Steel Sheets and Treatment Methods for Alkali Reversion

First: Causes of Alkali Reversion (White Rust, Black Spots)

1. Principle of White Rust Formation on Galvanized Steel Sheets: When galvanized steel sheets are densely packed and placed in humid air, without free air flow across the surface, electrochemical corrosion of the zinc layer occurs, resulting in the formation of white rust. Condensed water on the zinc surface combines with oxygen, carbon dioxide, hydrogen sulfide, sulfur dioxide, oxides, and other chemical gases to produce a corrosive aqueous solution that adheres to the zinc surface, forming an electrolyte. This electrolyte electrochemically corrodes the zinc layer, resulting in visible white rust, a powdery substance (zinc oxide). The secondary and tertiary oxidation products of white rust, which form a localized black surface, are collectively referred to as alkaline reversion.

2. Impact of White Rust on Galvanized Steel Sheets: Because metallic zinc increases in volume 3-5 times when converted to zinc oxide or zinc hydroxide, the resulting white rust is larger, making the corrosion appear much more severe than it actually is, severely affecting the appearance of the zinc layer. However, it actually only causes minimal zinc loss on the surface.

3. Treatment of White Rust on Galvanized Steel Sheets: A large amount of white rust may appear on the surface of galvanized steel sheets, but the corrosion to the zinc layer is relatively minor. In most cases, the appearance of white rust does not indicate serious damage to the zinc layer. After white rust occurs, the galvanized steel sheets should be laid out to allow the surface to dry quickly.

As mentioned above, alkali rust is a common phenomenon on galvanized products in the summer due to factors such as weather, transportation, and storage. As long as the zinc layer remains above the standard after corrosion, it will not affect the product's service life.

Second: Storage Precautions for Galvanized Steel Sheets

1. All galvanized steel sheets will develop white rust in humid, high-temperature, poorly ventilated, or corrosive environments. Products particularly prone to white rust: Water accumulation inside tightly packaged and sealed products, such as angle steel, flat iron, square and rectangular tubes, and round tubes, coupled with hot and humid weather, can easily lead to alkali rusting in galvanized products.

2. Upon arrival at the destination, galvanized steel sheets should be stored in a well-ventilated warehouse and should not be stacked in areas with high levels of harmful gases or dust.

3. If slight white rust or spots appear on the surface, they should be immediately disassembled and aired. Air them until the white rust turns to powder, and then they should be brushed off immediately.

4. In hot and humid environments, store indoors, maintain ventilation and dryness, and avoid direct contact with moist soil when stacking.

5. Galvanized steel sheets are not susceptible to high temperatures, humidity, or concentrated storage, but are susceptible to all three conditions, namely, concentrated storage in hot and humid environments.