Predictable Performance
Hot dip galvanizing provides the most effective form of corrosion protection for fabricated steel. During the HDG process the zinc coating forms a chemical bond with the steel, to become part of the physical structure. This creates 3 layers of protection for predictable performance:
- Barrier protection is the physical envelope of galvanizing around the steel. In hollow sections, i.e. pipes, this envelope is internal & external.
- Zinc patina reduces the exposure of the galvanizing coating to the environment
- Cathodic protection from the surrounding galvanizing coating protects small areas of exposed steel from corrosion.
Corrosion Zones
The corrosion resistance of galvanized coatings in the atmosphere, soil, concrete and in most natural waters is due to the patina, which acts as a protective layer. Once stabilized, the patina greatly reduces the reaction rate between the HDG coating and the environment, for long term corrosion protection.
An environment’s corrosivity may vary due to local conditions, such as prevailing winds in coastal areas, atmospheric gases and chemicals in industrial areas, atmospheric moisture and micro-environments created by fertilisers in rural areas.
Life Cycle Cost Benefits of HDG
Hot dip galvanizing not only outperforms paint coatings for the service life of corrosion protection for steel structures, often the upfront costs are cheaper and the total life cycle cost benefits are significant. For example, in a C4 Corrosion Zone or a Highly Corrosive Environment, HDG has an expected service life of 20-40 years, compared to a 10-15 years of service life for epoxy high build paints.
In addition to direct maintenance costs associated with surface preparation and re-application of paint, further indirect costs apply, i.e. site accessibility, loss of productivity during maintenance, energy to transport labour and materials to site, along with particulate emissions caused by surface preparation blasting.
This comparative table highlights the upfront and service life cost benefits of HDG compared to a range of primary paint coatings for steel.
