CORROSION RESISTANCE METHODS FOR STRUCTURAL STEEL BASIC AND TUTORIALS

CORROSION RESISTANCE METHODS FOR STRUCTURAL STEEL BASIC INFORMATION
What Are The Corrosion Resistance Methods For Structural Steel?

Since steel contains three of the four elements needed for corrosion, protective coatings can be used to isolate the steel from moisture, the fourth element. There are three mechanisms by which coatings provide corrosion protection (Hare, 1987):

1. Barrier coatings work solely by isolating the steel from the moisture. These coatings have low water and oxygen permeability.

2. Inhabitive primer coatings contain passivating pigments. They are low-solubility pigments that migrate to the steel surface when moisture passes through the film to passivate the steel surface.

3. Sacrificial primers (cathodic protection) contain pigments such as elemental zinc. Since zinc is higher than iron in the galvanic series, when corrosion conditions exist the zinc gives up electrons to the steel, becomes the anode, and corrodes to protect the steel.

There should be close contact between the steel and the sacrificial primer in order to have an effective corrosion protection.

Cathodic protection can take forms other than coating. For example, steel structures such as water heaters, underground tanks and pipes, and marine equipment can be electrically connected to another metal that is more reactive in the particular environment, such as magnesium or zinc.

Such reactive metal (sacrificial anode) experiences oxidation and gives up electrons to the steel, protecting the steel from corrosion. Figure 3.32 illustrates an underground steel tank that is electrically connected to a magnesium sacrificial anode (Fontana and Green, 1978).



Above is a diagram on Cathodic protection of an underground pipeline using a magnesium sacrificial anode.

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