Galvanizing is unique - tough, long lasting, self-healing and covers internal and external surfaces. Here we highlight the benefits of barrier and sacrificial protection:
Galvanizing provides a barrier between all internal and external steel surfaces and their environment. Galvanizing is a term often wrongly used to describe zinc coatings in general. The diagram below illustrates how the different types of zinc coatings vary in terms of coating thickness. The life expectancy of a zinc coating is largely determined by its thickness. Thicker coatings give longer life. Hot dip galvanizing provides fabricated iron or steel products with maximum protection through a continuous, tough, metallurgically bonded coating of much greater thickness.
Zinc corrodes in preference to steel and sacrifices itself to protect the steel, hence hot dip galvanizing will provide this sacrifical action. 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 break down of the whole coating as rust crept underneath the paint film.
A galvanic cell is formed. The zinc around the point of damage corrodes. Corrosion products precipitate on the steel surface and protect it. The steel is also protected because it is cathodic in relation to the zinc coating.
The steel rusts where the paint film has been damaged. Rust creeps under the paint film, which is lifted up from the steel surface. Corrosion continues until the damage has been repaired.
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.
Schematic to illustrate the consequence of damage to
different types of coating offering corrosion protection