'Galvanizing is the biggest and fastest growing method of coating steel with a protective metal.'

This results from steadily rising maintenance costs and therefore ever increasing benefits are gained from long term maintenance-free coatings.

The facts are these:
The problem
Steel generally corrodes between 0.05mm and 0.125mm per year when freely exposed to air. However, in heavily polluted regions this rate can increase considerably. In many situations the natural corrosion rate would be acceptable purely from a safety point of view, but the appearance of flaky rust on steel is generally unacceptable. The protection therefore is more often than not to preserve the general appearance rather than the structural strength of the material.

The advantages
a) Galvanizing is a versatile process and articles in size from nuts and bolts to structures 450m high have been protected. However, generally almost
any structure can be galvanized.

b) A thick zinc alloy protective coating metallurgically and permanently bonded to iron or steel base. Zinc corrodes only 3 to 10 percent as fast as steel in air and the standard coating lasts up to 25 years even in industrial, urban or marine atmospheres. It also resists many chemicals, waters, alkalis and building materials.

c) In galvanizing the absence of defects will ensure a better quality coating, particularly where appearance is important. An even thickness of zinc covers both edges and flat surface giving complete protection to what are potentially corrosion spots in other systems.

d) Galvanizing applies a tough coating. The alloy layer is harder than mild steel and with the softer zinc outer layer, provides the ideal buffer-stop coating to withstand knocks and abrasion.

Galvanizing
When immersed in the galvanizing bath, iron or steel are immediately wetted by the zinc and react to form zinc-iron layers. As the work is removed from the bath, some molten zinc is taken out on top of the alloy layers, the whole coating being metallugically bonded to the basis metal.

At the normal Galvanizing temperatures of 445-465 deg centigrade, the rate of reaction is very rapid at first, with a 'boiling off' action. The main thickness of coating forms during this initial period and it is therefore impractical for the galvaniser to form a very thin coating. The normal period of immersion is a minute or two but longer for work that requires draining from internal spaces or is particularly heavy.