Benefits of Hot-dip galvanizing
HDG provides great resistance
Once the freshly cleaned material is submerged in the molten zinc bath @ 450C (840 degrees F), a metallurgical bond is created, composed of intermetallic layers and a pure zinc layer.
The first intermetallic layer is actually harder than the base steel. This quality is what gives galvanized steel its great impact and abrasion resistance. The soft, pure zinc layer helps absorb some of the shock and the intermetallics protect the base material.
Microphotography of metallic coating
Coating service life is foreseeable as long as climate conditions - to which the coatings are exposed - are known.
The ASTM has published the results of a research conducted in different environments where zinc coatings could be exposed to a variety of climate conditions.
Rust takes its toll on painted surfaces.
Here is what happens to painted steel when scratched... The exposed steel corrodes and forms a rust "bubble". This "bubble", larger than the surface occupied by the steel, will expand and lift the paint off the surface, creating a blister. In the meantime, the corrosion cavity and the blister continue to progress.
Galvanizing offers sacrificial protection
Here is what happens when galvanized steel is scratched... Thanks to its galvanic protection, the zinc coating sacrifices itself to protect the steel to which it is bonded. This sacrificial protection will prevail as long as zinc is within proximity.
Should the hot-dip galvanized coating be damaged or scratched, the steel will find protection against corrosion thanks to the surrounding zinc that has higher electrochemical properties than those of steel.
Since corrosion is an electrochemical process, it will attack the surrounding zinc rather than the exposed steel. Contrary to other types of processes claiming to provide corrosion protection, it is not required to touch-up noticeable cracks, flaws or gaps on galvanized coatings as they are self-healing.