Does Galvanized Steel Rust?

How Long Will It Take For Galvanized Steel To Rust?

The rust time of galvanized steel is determined by the environment in which it is used.

If the galvanized steel sheet is left outdoors for a long time, the galvanized steel sheet will rust, the service life is about seventy years.

If galvanized sheet is placed indoors and kept dry and don’t let the galvanized sheet get water stains and corrosive liquid, so the rust time of the galvanized sheet will be prolonged. It can generally be used permanently without rust and corrosion.

Galvanized steel sheet is also divided into cold-dip galvanized steel sheet and hot-dip galvanized steel sheet. Generally, cold-dip galvanized steel sheet is easier to rust, while hot-dip galvanized steel sheet is not easy to rust.

Under normal circumstances, the corrosion of galvanized sheet is not that the galvanized layer on the surface is uniformly corroded, but the coating is corroded first where the coating and the substrate are poorly bonded, resulting in severe local corrosion and loss of performance.

From this point of view, the adhesion of the galvanized layer, especially the overall adhesion, is more important than the thickness of the galvanized layer. If the galvanized layer has poor local adhesion, even if the galvanized layer is thicker, it will start to rust from the poor adhesion.

Why Does Galvanized Steel Rust?

  1. The plating layer is not uniform, and there is a missing area. Galvanized steel sheets with uneven thickness are likely to rust first.
  2. The surface is damaged during transportation or installation, resulting in weakening of the anti-rust ability.
  3. The zinc layer is too thin and the corrosion resistance is poor.
  4. When exposed to acid rain and other chemicals, it accelerates rusting.
  5. The zinc plate is not pure and contains impurities.
  6. It is more prone to corrosion if it is wetted by acid rain or there are chemical substances in the warehouse or there are chemical plants nearby.

How Does Galvanized Steel Rust?

During the entire service life of the galvanized sheet, the first corrosion that occurs is the oxidation of the galvanized layer on the surface to form “white rust”. After a little longer time, the “white rust” on the surface will further react with impurity gases such as carbon dioxide in the moist gas to form “black spots”.

When the galvanized sheet is used for a long time, the corrosion of the galvanized layer is severe, and the steel base loses the “sacrificial anti-corrosion” effect of zinc, and begins to oxidize to form “red rust”. When the steel base starts to oxidize and corrode, the speed becomes very fast, “the galvanized sheet also ends its life.

In addition, there are two special corrosion conditions of the galvanized sheet called “blackening”. One is that after the galvanized sheet is used for a period of time, due to the influence of elements such as lead in the galvanized layer, the matte part of the spangle will turn black.

The blackened galvanized layer still has a protective effect on the steel base, but it has a certain impact on life. This situation has been greatly improved after the current suspension of lead and the use of antimony to promote the formation of spangles. Another situation is that the galvanized sheet is transported.

Due to the small coiling tension, the steel strip layers are loose, and the parts of the steel coil contacting the skid will rub against each other and cause oxidation. After the white oxide is rubbed off, the plating Black spots are produced on the surface of the zinc sheet, which will destroy the passivation film, thin the galvanized layer, greatly reduce the life of the galvanized sheet, and affect the appearance.

How Do You Keep Galvanized Steel From Rusting?

  1. Avoid quality problems such as insufficient passivation or insufficient thickness.
  2. Pay attention to the drying of water stains on the surface of the steel plate and keep it dry.
  3. Do a good job of smooth transportation and anti-scratch measures.
  4. Improve the storage conditions for storing steel plates, and the storage time should not be too long.
  5. The steel plate should be passivated with good passivation products.

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