Understanding White Rust: Causes and Prevention

White rust is a type of corrosion that can affect the strength of galvanized steel. It shows up as a chalky, white coating on its surface. It forms when galvanized steel is exposed to moisture without adequate airflow, causing the zinc coating to react with water and form zinc hydroxide.

Understanding what causes white rust is essential for prevention and maintenance. In this article, we will examine the characteristics of white rust, explore its causes, discuss its effects, and outline strategies to prevent its occurrence.

What Is White Rust？

White rust is a chalky, white corrosion that forms on the zinc coating of galvanized steel. It occurs when freshly galvanized steel is exposed to moisture without proper air circulation. severe white rust can weaken the protective zinc layer, reducing corrosion resistance. A dry, well-ventilated storage environment and passivation treatment after galvanizing can prevent the formation of white rust.

What Is the Difference Between Rust and White Rust?

Rust typically appears as reddish-brown flakes caused by iron oxidation, while white rust is a powdery, white residue that forms on zinc-coated surfaces. They indicate different types of corrosion processes.

What Causes White Rust on Galvanized Steel?

Feuchtigkeit

White rust on galvanized steel is primarily caused by moisture. When water collects on the surface, it interacts with the zinc coating, resulting in the creation of zinc hydroxide and, over time, zinc carbonate. This reaction often occurs in conditions where humidity is high.

For instance, galvanized steel structures like fences or roofing can develop white rust if they are exposed to prolonged rain without adequate drainage.

Contaminants

Contaminants also play a critical role. When galvanized steel is exposed to saltwater, such as near coastlines, or polluted air in industrial areas, the risk of white rust increases. Salts and pollutants can attract moisture, accelerating the corrosion process.

Improper Storage

Another scenario is when galvanized products are stacked or stored improperly. If water collects between stacked sheets or components, the confined moisture can promote white rust. Ensuring proper spacing and ventilation during storage can help minimize these risks.

What Are The Effects of White Rust?

White rust can have several effects on galvanized steel, impacting both its appearance and structural integrity. At first, white rust might appear to be a minor surface issue. However, as it develops, it creates multiple problems for galvanized steel.

It harms the zinc layer, leaving the steel exposed and increasing its vulnerability to corrosion. This exposure can also weaken the metal’s strength, affecting its load-bearing capacity. Additionally, white rust results in an unsightly, chalky appearance that detracts from products like fences and outdoor furniture.

Can White Rust Spread?

Yes, white rust can spread if left untreated. It occurs when moisture and contaminants react with the zinc coating, leading to further corrosion. Consistent monitoring is crucial for early detection.

How to Prevent White Rust on Galvanized Steel？

Lagerung

1. Always store galvanized steel in a dry, well-ventilated space. For example, keeping it indoors or under a protective shed can minimize moisture exposure.
2. Elevate the steel off the ground using pallets. This keeps water from accumulating at the base and promotes air circulation, lowering moisture levels.
3. When storing multiple pieces, avoid stacking them too closely. Allow gaps between items to enhance air circulation and reduce moisture accumulation.
4. If the steel must be stored outside, use breathable tarps or covers. This will protect it from rain while allowing moisture to vent out, reducing the risk of condensation.

Anmeldung

1. Before using galvanized steel, check for any existing white rust or damage. Addressing issues at this stage can save time and prevent future problems.
2. If the steel has been exposed to dirt or contaminants, wash it with mild soap and water. Ensure it is thoroughly dried to remove any residual moisture.
3. During installation, ensure that the design allows for proper drainage. Avoid flat surfaces where water can collect, and consider sloping designs for outdoor applications.
4. In moisture-rich or salt-exposed environments, use a suitable protective coating. This extra layer can help shield the zinc finish from corrosive elements.

Passivation Process to Prevent White Rust

Beyond proper storage methods and routine maintenance, passivation treatment after galvanizing plays a crucial role in managing white rust. This additional protective step helps shield the zinc coating from rapid oxidation when exposed to moisture, reducing the risk of white rust formation.

Chromat-Passivierung

Chromate passivation involves applying a chromic acid solution to galvanized steel. This creates a thin protective layer of chromium compounds that enhances corrosion resistance. It effectively prevents white rust and extends the lifespan of galvanized products.

Chromatfreie Passivierung

Chromate-free passivation uses alternative chemicals, such as organic compounds or zinc salts, to protect the galvanized surface. While not as robust as chromate methods in extreme conditions, they still effectively prevent corrosion. Common types include:

• Zinc Phosphate Coating
• Zinc Silicate Coating
• Keramikbeschichtungen
• Silane Treatments

When Is Passivation Most Suitable?

The ideal time for passivation is immediately after galvanization. This process seals the surface and improves corrosion resistance before exposure to environmental conditions. Early application maximizes protective benefits and reduces the risk of white rust.

Limitations of Passivation

Both passivation methods have limitations. Chromate treatments pose environmental risks due to chromium, while chromate-free options may lack robustness in harsh settings. Chromate passivation is still used in some applications where its superior corrosion resistance is needed, but the trend is toward increasing the use of non-chromate options.

If white rust appears, it must be removed before applying passivation again to ensure effective protection.

How To Remove White Rust From Galvanized Metal?

Firstly, inspect the galvanized surface to assess the severity of the white rust.

For Mild Cases of White Rust

1. Create a cleaning mixture by combining equal parts of white vinegar or citric acid with water.
2. Use a soft brush to lightly scrub the affected surface with the solution.
3. Rinse thoroughly with clean water to wash away any leftover residue.
4. Allow the surface to dry completely to prevent new rust from forming.
5. Consider applying a passivation treatment or a zinc-rich coating for added protection.

For Severe Cases of White Rust

1. Put on protective equipment, such as gloves and safety goggles, and make sure there is sufficient ventilation.
2. Use a soft-bristled wire brush to carefully clear away most of the white rust.
3. Apply a strong rust remover, following the manufacturer’s instructions for a product safe for galvanized metal.
4. Thoroughly wash the surface with clean water and neutralize any remaining residues.
5. Allow the surface to dry, then consider applying a passivation treatment or a zinc-rich coating for enhanced protection.

Does Vinegar Remove White Rust?

Yes, vinegar can effectively remove white rust due to its mild acidity. However, when using vinegar, be careful not to leave it on the surface for too long, as prolonged exposure can damage the zinc coating. Always rinse the area thoroughly with water after treatment to neutralize the acidity.

Durable Galvanized Steel Solutions

At Steel Pro Group, we ensure that galvanized steel is stored in optimal conditions—dry, well-ventilated, and free from moisture buildup. With our advanced passivation treatment options, we provide extra protection to minimize the risk of white rust and extend the life of your products.

Protect your steel for the long haul with Steel Pro Group’s innovative corrosion solutions. Explore how our products are designed to withstand the harshest environments and keep your investments strong.