What Is White Rust on Galvanized Steel?

White rust on galvanized steel is a common problem when it is stored in a humid and poorly ventilated environment. Generally, after long-term transportation, large amounts of white or grey powder will appear on the surface of the zinc layer, which is commonly referred to as white rust.

What Is White Rust on Galvanized Steel?

White rust, in the form of a lumpy, white or gray powder, is essentially zinc hydroxide, a corrosion product that adheres to the surface of galvanized steel. It is usually produced when galvanized steel is transported for a long period of time or stored in humid, poorly ventilated environments where the surface zinc layer is damaged by oxygen or other elements in the air.

What is the cause and process of white rust formation?

White rust is a problem that occurs on galvanized steel, galvanized copper, and other galvanized metal surfaces. So why does white rust occur? First of all, the zinc coating of galvanized steel is highly reactive, and it reacts with atmospheric elements such as carbon dioxide to form stable oxides, which give galvanized steel its corrosion resistance. However, these oxides are formed gradually and are susceptible to corrosion as there is no oxide layer at the time of initial production. So in this situation, if GI steel is exposed to an environment with a high moisture content and a low oxygen content, the zinc coating on its surface will react with the environmental elements to form unstable zinc hydroxide, which is no longer a stable oxide.

This unstable compound is what we call white rust, which slowly corrodes the zinc coating and exposes the galvanized steel to further moisture and other corrosive elements.

5 Causes of White Rust

1. High air humidity

2. Oxygen content in the air is too low, such as acidic gases accounting for a large proportion of the environment

3. Direct contact with other metals

4. Packaging without thorough drying

5. Storage crush with mechanical damage

What factors should be considered to prevent white rust?

1. Freshly made galvanized steel needs to be protected first, it is the most vulnerable to damage.

2. Galvanized steel products should be stored away from environments with high humidity.

3. It should also be stored in a well-ventilated environment to ensure adequate air circulation.

Preventive measures for white rust on GI steel

In light of the above considerations, the first and most obvious measure would be to store your stock of galvanized steel indoors. The indoor temperature should be above the dew point.

1. Ensure that galvanized steel and galvanized coil products do not directly touch the ground, avoid stacking too tightly, and ensure air circulation.

2. Keep away from acid, alkali, salt, cement, lime, and other substances.

3. Cool down immediately after hot-dip plating, apply antirust oil, paint, or passivation treatment.

4. When stored outdoors, not stacked directly on wet soil or decayed vegetation, it is best to cover with a rainproof cloth or build a simple scaffolding to provide additional protection, avoiding the open air for too long.

5. Thoroughly dry before packing and regularly check the storage location. Especially in summer, high temperatures and frequent rain showers will lead to drastic changes in the storage environment, so more attention should be paid to it, using desiccant to dehumidify the area if necessary and stacking them in piles spaced apart with wooden strips.

6. When shipping, use wooden strips to separate and use anti-rust desiccant and other packaging to avoid condensation on the surface and reduce the formation of white rust.

Therefore, it is easier to prevent white rust than to cure it. Always make sure that galvanized steel in stock is properly protected.

Is White Rust Harmful?

Since the volume of metallic zinc increases by 3 to 5 times when it is converted into zinc oxide or zinc hydroxide, the white rust formed is larger in volume. As a result, white rust looks much more severe than it actually is, seriously affecting the appearance of the zinc coating. But in fact, white rust rarely affects the underlying zinc layer. Generally speaking, a small amount of white rust will not affect the anti-corrosion performance and the service life of the coating, and it will gradually disappear as the surface of the galvanized steel dries. However, if the galvanized metal is stored or transported in a humid environment for a long time, the white rust may not only affects the appearance of the product but also reduces its service life. You may better understand it when you know the rusting process of galvanized steel.

How to Remove White Rust from Galvanized Metal?

1. Mild White Rust: The surface of the galvanized parts can be wiped with a clean cloth to remove the white rust powder from the surface and apply the necessary rust preventive treatment.
2. Heavy White Rust: For moderate to heavy white rust, the surface can be removed with a mechanical rust removal tool or surface treated with an appropriate rust remover. After removing the white rust, the thickness of the coating in the area where the white rust was generated must be checked to ensure that sufficient galvanizing is left to protect the steel base.

What Can Wanzhi Steel Offer?

1. There is a sufficient and good storage environment.
2. Adopt advanced passivation treatment methods and natural drying after passivation.
3. Slickly package according to regulations. Our galvanized steel coils and sheets are often packaged with waterproof kraft paper, plastic film inside, and galvanized sheets outside and then tied up with 6-8 steel strips.
4. We will remind our clients of some prevention tips.

Some Tips for White Rust

1.  Make sure there is no condensed water on the surface before packaging;
2. Apply oil and passivation to the surface of the galvanized steel products;
3. Different kinds of steel should be stacked separately;
4. Keep air circulation in the warehouse, and the humidity should not be in the range of 60% or 85~95%;
5. Galvanized steel should be stacked away from harmful gases and excessive dust;
6. Avoid rain and water leakage during packaging or transportation;
7. Deal with the white rust in time.

Conclusion

Due to weather, white rust on galvanized steel is common in summer. White rust is easy to occur in humid, high temperature, airless and corrosive environments, especially angle steel and steel plates. When the galvanized products arrive at the destination, please pick up and unpack them in time and store them in proper environments. If there is slight white rust or spots on the surface, place the galvanized steel in dry and ventilated immediately. Until the white rust becomes powdery, wipe it off with a brush or dry cloth in time. At Wanzhi Steel, our products are made in accordance with the contract standards. Besides, we will stock and package our products properly. And we will update the shipping information in time. If you have any questions, please feel free to contact us!