Barrier and sacrificial protection
What is barrier protection?
Barrier protection
Galvanizing provides a barrier between all internal and external steel surfaces and their environment so that corrosion will not occur. Galvanizing is a term often wrongly used to describe zinc coatings in general. The adjacent diagram 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.Â
What is sacrificial protection
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 filmÂ
how does zinc provide sacrificial protection?
The diagram on the left illustrates how the sacrificial action of zinc protects the steel underneath. 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. The steel is also protected because it is cathodic in relation to the zinc coating. (Read more on cathodic protection.)
When a paint coating is damaged, no sacrificial protection is offered and the underlying steel will corrode as it is exposed to the atmosphere. The rust which forms can then begin to undercut the paint coating which increases the area of damage and the area required for repair.
The unique nature of the galvanizing process provides a tough and abrasion resistant coating which means less site damage and speedy erection of structures.
Galvanizers Association can provide detailed advice on compiling your specifications for galvanizing your steel, reviewing design details to maximise the benefits, as well as galvanizing standards. Learn more about the galvanizing standards.
How long will galvanizing last in your area?
How can you paint galvanized steel?
