Why does galvanized steel appear white rust?

1. What is galvanized steel white rust?

White rust is a wet storage stain, a white or grey powdery deposit that may form on newly galvanized items. It occurs when galvanized steel is exposed to rain, dew, or high humidity condition. White rust is the formation of zinc oxide and zinc hydroxide visible on the surface of galvanized steel. It is important to note that the hot dip galvanizing process does not lead to the formation of wet storage stains. Staining occurs after the coating has reacted with the environment, not during the coating process.

1) When a newly galvanized coil product loses sufficient airflow, moisture may be trapped on the surface of the coating, thereby altering the natural development of zinc-bronze green.

2） Trapped moisture creates a range of different conditions that can create a reaction that results in the rapid formation of white powdery zinc corrosion products on the surface. When a drop of water is flattened between two surfaces, the zinc surface near the middle of the drop receives a different supply of oxygen than the zinc surface at the edge of the drop. The different exposures result in differences in the electrolytic potential of the zinc. The center region may become the anode and the edge region may become the cathode, resulting in the formation of a potential corrosion cell. If a corrosion cell is formed, the anodic region begins to corrode while the cathodic region remains unchanged. Corrosion products of soluble zinc hydroxide similar to zinc patina form on the surface.

3）As zinc hydroxide remains fairly stable under these conditions, the zinc ions continue to leave the coating and combine with water to form a thick and visible white powdery substance. As long as the area is restricted by oxygen, it also restricts the flow of carbon dioxide, which prevents the conversion of zinc carbonate. The extent to which wet storage stains consume the zinc coating depends on the duration of exposure to trapped moisture without free-flowing air. If the trapped moisture contains chlorides (from seawater, sulfur compounds, flux residues), erosion will be accelerated because these contaminants increase the conductivity of the water and thus increase the erosion of the zinc metal of the galvanized coating.

4）During transport, chloride-rich moisture from road salt may be trapped on the steel, even under a tarpaulin, and cause wet storage stains.

5) However, even water alone can lead to the formation of wet storage stains in a relatively short period. After the galvanizing layer has formed, exposure to heavy rain, dew, or very high humidity conditions will start the formation of visible zinc oxide and zinc hydroxide.

Other supplier’s white rust on galvanized steel

Jianhui Steel Mill Galvanized  Steel

Generally speaking, the appearance of white rust on galvanized steel is often caused by transportation or storage, because the occurrence of white rust means that the steel coil is in a state of high humidity, or even soaked in water. Condensation phenomenon, which is also very easy to cause white rust. The main reasons for galvanized steel white rust are:

(1) Poor passivation, insufficient or uneven thickness of the passivation film;

(2) The surface is not oiled or there is residual water on the surface of the strip;

(3) The strip surface contains moisture during coiling;

(4) Passivation is not completely dried;

(5) Damp or rain during transportation or storage;

(6) The storage time of finished products is too long;

(7) The galvanized steel is in contact with or stored together with other corrosive media such as acid and alkali.

2. To avoid white rust on galvanized steel, Jianhui Steel factory  recommends:

(1) When ordering, choose different treatments according to the subsequent use conditions: including chromic acid treatment, oiling, phosphate treatment, or anti-fingerprint treatment;

(2) The galvanized steel is covered with a rain cloth during transportation, no matter whether it is raining at that time or not, if it is shipped by ship, avoid soaking in a glass of water;

(3) The galvanized steel should be stored in a well-ventilated and high-lying place. If the humidity is too high, a dryer can also be considered;

(4) If condensation occurs or is soaked with water, unpack it and dry it as soon as possible; for white rust that has been generated, it can be wiped off with a cloth soaked in oxalic acid, then rinsed with water and dried;

Follow the principle of first come first use and use as soon as possible to avoid long-term storage of galvanized steel.

If the galvanized steel produces a slight white patch, it can be wiped off with a damp cloth, but not with a wire. Specific steps: It can be removed by repeatedly wiping with a damp cloth with a little water. Be careful not to use too much water, and do not wipe with sharp objects such as steel balls.

The area of ​​the galvanized steel white spot is relatively large, and it needs to be re-plated after pickling. Or for local repair coating, spray paint after treatment with our special galvanized coating pre-treatment products.

3. How to remove white corrosion on galvanized steel metal?

To remove white corrosion on galvanized steel, you can follow these steps:

Materials You’ll Need:

1. Water

2. Mild dish soap or detergent

3. White vinegar or lemon juice

4. Soft-bristle brush or sponge

5. Non-abrasive cloth or rag

6. Rust-resistant primer

7. Rust-resistant paint (matching the original color, if desired)

8. Protective gloves

9. Safety goggles

Steps:

1. Safety First:

Put on your protective gloves and safety goggles before starting the cleaning process.

2. Preparation:

Begin by mixing a solution of water and mild dish soap or detergent in a bucket. This will serve as your cleaning solution.

3. Clean the Surface:

– Dip the soft-bristle brush or sponge into the cleaning solution.
– Gently scrub the corroded areas of the galvanized steel to remove loose dirt, debris, and any surface oxidation. Avoid using abrasive materials that could scratch the surface.

4. Rinse:

Rinse the cleaned areas thoroughly with clean water to remove any residue from the cleaning solution.

5.  Acidic Treatment:

– If the white corrosion persists, you can try a more aggressive approach using white vinegar or lemon juice.
– Apply a small amount of white vinegar or lemon juice directly onto the corroded areas.
– Let it sit for a few minutes, but don’t let it dry on the surface.
– Scrub the corroded areas gently with the soft-bristle brush or sponge to help lift the corrosion.

6.  Rinse Again:

Once again, rinse the treated areas thoroughly with clean water to neutralize and remove any remaining acid.

7.  Drying:

Allow the galvanized steel to air dry completely.

8. Priming and Painting (Optional):

– To prevent further corrosion, you can apply a rust-resistant primer to the cleaned and dried areas. Follow the manufacturer’s instructions for application.
– After the primer is dry, you can apply rust-resistant paint that matches the original color if you wish. This will not only improve the appearance but also provide an additional layer of protection.

Remember, prevention is key to maintaining galvanized steel. Regular cleaning, keeping the surface dry, and addressing any sources of moisture will help prolong the life of the galvanized coating.

Always follow safety precautions, and if the corrosion is extensive or the structure is load-bearing, it’s recommended to consult a professional for guidance on restoration or repairs.

Summary:

Jianhui Steel Factory since its inception in 2005, Jinahui Steel factory has grown to become the largest manufacturer of PPG , GI steel in China .An ISO 9001-certified company White embroidery does not occur in Jianhui Steel galvanized coils.