Hot dip galvanized steel is a steel covered in zinc coating to protect the steel from corrosion. In the galvanizing process, the steel is cleaned and dipped in a bath of molten zinc solution at temperature of approximately 450 degrees.
Liquid zinc sticks to the metal and when the metal is pulled out of bath the zinc gets hardened. As a result there is a really hard outer coating of zinc which protects the inner steel core from corrosion and other types of moisture.
- Barrier Protection
Barrier protection is the oldest and widely used method for protection against corrosion. It isolates the base metal from the environment. Just like paints, hot dip galvanizing coating provides barrier protection to steel. As long as the barrier is intact, there is no corrosion and the steel is protected. If the barrier gets breached, the corrosion starts.
Two most important properties of barrier protection are abrasion resistance and adhesion to base metal. The impervious and tightly bonded nature of zinc makes galvanizing a good barrier coating. Coating like paint which have pin holes can be penetrated by elements which causes rapid under film corrosion.
- Cathodic Protection
Cathodic protection is an effective way for protection against corrosion. It requires changing an element of corrosion circuit by introducing a new corrosion element which ensures that the base metal becomes cathodic element of the circuit.
In case of hot dip galvanizing zinc will either corrode or protect to protect the underlying base steel. The cathodic protection ensures that even if the coating gets damaged to the point bare exposed steel, no corrosion will start until the surrounding zinc gets consumed.
- Zinc Patina
Zinc patina protects zinc coating unlike cathodic and barrier protection which resist corrosion to steel. Zinc begins to corrode when exposed to atmosphere like all metals. Freshly galvanized steel can naturally wither when exposed to dry and wet cycles in the environment.
Fully developed zinc patina is passive and stable film that sticks to the zinc surface and is not soluble to water so it does not get washed off in rain or snow. Zinc patina gets corroded very slowly and protects galvanized coating underneath which brings down the corrosion rate of the steel in the same environment.
As the development of zinc patina takes place, galvanized coating turns in a matte grey color. Zinc patina formation is very important in long-lasting corrosion resistance of hot-dip galvanizing.
Hot dip galvanized coating is resistant to mechanical stress. The resistance is twenty times higher than resistance of PVC coatings and epoxy dust coatings and eight times higher than resistance of epoxy coatings.
One of the advantages of hot-dip galvanizing is there is no doubt about quality as you cannot apply zinc coating to an unclean steel surface while it is possible on the other hand when applying paint.
One of the advantages of hot-dip galvanizing is there is no doubt about quality as you cannot apply zinc coating to an unclean steel surface while it is possible on the other hand when applying paint.
Read more: Can Galvanized Steel be Painted? Precautions to Take
Thus, hot dip galvanizing is a far more lasting and better solution than paint to protect the corrosion of steel surfaces.