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Hot dip galvanizing has grown almost continuously since it was first used to protect corrugated iron sheets 150 years ago.

Hot dip galvanizing is the process of coating iron or steel with a layer of zinc by immersing the metal in a bath of molten zinc. During the process, a bonded coating is formed which protects the steel from harsh environments.

Galvanizing is probably the most environmentally friendly process available to prevent corrosion. Data shows that galvanizing can provide between 34 to 170 years of protection for steel.

Sacrificial protection

Zinc corrodes in preference to steel and sacrifices itself to protect the steel, hence hot-dip galvanizing will provide this sacrificial protection.

The corrosion products from the zinc are deposited on the steel resealing it from the atmosphere and therefore stopping corrosion.

With paint coatings, additional protection would have to be applied immediately after the damage occurred or the steel would rust with eventual breakdown of the whole coating as rust crept underneath the paint film.

A hot-dip galvanized coating that is damaged
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A hot-dip galvanized coating that is damaged. At the point where the galvanized steel suffers damage, a galvanic cell is formed. The zinc around the point of damage corrodes. Corrosion products precipitate on the steel surface and protect it.

A paint coating that is damaged
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Let’s now think about what happens if you coat your steel with a more electro-positive metal such as Nickel, chromium and copper. As they fall below steel in the galvanic series, they give rise to more rapid corrosion at the point of damage than if the steel had been uncoated. The steel actually sacrifices itself in favour of the chrome, which is the opposite of what we are striving for when it comes to rust protection.

Coating of more electro-positive metals than steel
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Nickel, chromium and copper give rise to more rapid corrosion at the point of damage than if the steel had been uncoated. The corrosion often takes the form of pitting, which can even go through the steel.

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