Can galvanized steel rust?

(2) In harsh environments

In industrial areas where acid rain is frequent and in seaside environments where salt spray is severe, the zinc layer of galvanized steel depletes at an accelerated rate and rust spots may appear within 5-10 years. Research by the Chinese Society of Corrosion and Protection shows that the service life of galvanized steel on the seashore is about 1/3 of that of inland environments.

(3) After the zinc layer is damaged

When the plating layer is damaged due to scratches, impacts, etc., and the steel substrate is directly exposed to air and moisture, corrosion will occur rapidly. This is a situation that must be avoided in engineering applications. Therefore, galvanized steel does not “never rust”, but is significantly better than ordinary steel under the same conditions.

3. The causes of galvanized steel rust

(1) Air environment factors

Oxygen and water vapor in the air is one of the main factors leading to the rusting of galvanized steel. If the air is humid and the oxygen content is high, the zinc layer on the surface of galvanized steel will gradually oxidize and lose its protective effect, thus leading to rusting of galvanized steel.

(2) Conditions of use

Galvanized steel in use such as scratches, scrapes, etc., will destroy the zinc layer on the surface, resulting in the steel began to rust. In addition, if the conditions of use are poor, such as the use of acid rain, seashore and other environments, it is also easy to lead to steel rust.

(3) Differences in production processes

The production processes of galvanized steel are different, and the thickness and uniformity of the zinc layer on the surface of galvanized steel will be different, thus affecting the corrosion resistance of galvanized steel. Some informal manufacturers do not strictly follow the standard production, which may lead to uneven surface galvanization, thus affecting product quality.

4. Treatment of galvanized steel rust

After galvanization of steel products, if local rust is found, the treatment should take different measures according to the rust.

(1) A small amount of small point corrosion

rust point is shallow, accounting for a small amount of area, can be used to dip a wooden stick in dilute vinegar coated on the rust point, after standing for a while, wash with water. Then dry it with a cloth and apply transparent antirust paint on the rusted part.

(2) Localized corrosion

can be toothbrush or copper wire brush to brush off the surface rust spots, sprayed on the rusty parts of the lubricating oil or rust preventive agent, and then wiped dry with a cloth after a period of time.

(3) Serious corrosion

If cracks, structural deformation or large areas of spalling have occurred, only replacement parts can be used, and can not be completely repaired.

5. Methods of preventing rusting of galvanized steel    

In order to prevent rusting of galvanized steel, the following measures can be taken:

(1) Preventing humid environment

Galvanized steel should be avoided to be put in humid environment for a long time, and moisture-proofing agent can be used when storing it or moisture-proofing mats can be padded on the shelves.

(2) Maintenance

Regular cleaning, descaling, spraying and other maintenance of galvanized steel can effectively extend the service life of the steel.

(3) Select regular manufacturers

Purchasing should be verified that the thickness and uniformity of the plating is in accordance with national standards (such as GB/T 13912).

(4) Reduce mechanical damage

In the process of use, avoid steel from being hit, scraped, etc., and strictly prevent damage to the zinc layer on the surface.

(5) Protective Coatings

Appropriate protective coatings can be selected for surface treatment of galvanized steel, thus effectively slowing down the rate at which the steel is affected by the environment.

6. Six characteristics of galvanized steel

(1) Excellent corrosion resistance

The zinc layer can be insulated from air and moisture, even if partially broken, the zinc can still protect the steel through the role of “sacrificial anode”. According to the American Galvanizing Association (AGA) data, hot-dip galvanized steel in the ordinary atmosphere can be up to 50-100 years of service life, far more than ordinary steel 5-10 years.

(2) Cost-effective

Although the initial cost of galvanized steel is 10-20% higher than ordinary steel, the long-term maintenance costs are extremely low. For example, galvanized steel for bridges can reduce painting maintenance costs by 90% (Source: International Zinc Association).

(3) Good processing adaptability

Galvanized steel can be stamped, welded and bent, but note that the melting point of the zinc layer is low (about 420°C) and the temperature needs to be controlled when welding. Electro-galvanized steel is more suitable for precision stamping due to its uniform surface.

(4) Both aesthetic and functional

Hot-dip galvanized steel has a silver-gray crystalline pattern on the surface (commonly known as “zinc flowers”), while electro-galvanized steel is more subtle. Modern processes can also obtain colored coatings (e.g. blue-white, green-yellow) through passivation.

(5) Environmentally friendly

Zinc is 100% recyclable and the slag from the galvanizing process can be regenerated by the Waelz process. EU research shows that galvanized steel has 60% lower carbon emissions than stainless steel (source: European Steel Technology Platform).

(6) Wide range of applications

- Construction: roofing, steel frames (galvanization ≥275g/㎡, in accordance with GB/T 13912)

- Automobile: body panels (electro-galvanized layer thickness 7-15 microns)

- Electric power: transmission towers (hot-dip galvanized anti-corrosion life ≥ 30 years)

Galvanized steel is not absolutely rust-free, but its corrosion resistance far exceeds that of ordinary steel. As long as the galvanizing process is correctly selected, reasonably applied and properly maintained, its service life is fully capable of meeting the requirements for long-term durability in the construction, automotive, and home appliance industries.

As a cost-effective corrosion-resistant steel, galvanized steel will continue to play an important role in the future of construction, transportation, energy and industry, and will continue to be iterated and upgraded under the trend of green environmental protection.