How Galvanizing Delays Steel Corrosion

Corrosion or rusting occurs when iron or steel react with oxygen in the presence of moisture. In time, the metal may convert entirely to rust and disintegrate. Galvanizing applies a layer of protective zinc to isolate the metal from moisture and oxygen.  However, this is not a permanent solution because the sacrificial zinc eventually corrodes too.

Galvanizing is Not New Rocket Science

British colonists came across galvanized armour in the 17th century in India. Examples are still on show in the Royal Armouries Museum. This gave rise to the expression ‘galvanize into action’ but that’s another story.

Galvanizing protects the underlying iron or steel as follows:

# The zinc coating initially protects the entire underlying material by sacrificially corroding itself

# Exposed areas are still protected provided there is sufficient zinc nearby to electrically couple them

# After corrosion eventually consumes all the zinc, the protection fails and the underlying material rusts away

The Hot-Dip Method of Applying Zinc Iron Alloys

A thick, robust layer of hot-dip protection is achieved by submerging metal or iron parts in a bath of molten zinc, However it is usually possible to get away with a thinner layer where paint is applied afterwards e.g. in the motor industry.

Galvanizing is not the right solution for outdoor use in areas exposed to acid rain from sulfur oxide and nitrogen oxide emissions.  In these instances, more expensive stainless steel may prove cheaper in the long run.

Electroplating screws and bolts is a preferred solution over galvanization because it has minimal effect on thread size. However where there is a need for high precision then stainless steel or titanium is superior.

Galvanization in Construction and Other Applications

Construction is by far the commonest application. Typical examples are street furniture, building frameworks, balconies, verandas, staircases, ladders, and walkways. Galvanized water piping has been less successful. That’s because the metal rusts from the inside where the coating cannot reach.

While galvanizing will keep corrosion at bay for a while, rust is inevitable after several decades or sooner. Corrugated steel roof sheets may rust almost immediately in the presence of acidic conditions. Galvanizing soon fails under sea water because of its high electrical conductivity. Road salt has a similar effect on cars.

However, galvanizing can be an alternative to paint as long as you don’t mind your gazebo eventually rusting away. The above are among the many reasons Valiant Exteriors prefers other materials for the exterior of buildings.

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Rusting Corrugated Steel Roof Sheets: Peter Lewis BY Public Domain

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