Corrosion is defined as the destruction or degradation of a material (mostly metals) due to its interaction with the environment. This destruction takes place on the metal surface in the form of material dissolution or in some other forms, such as rust.
The Costs of Corrosion
According to SSPC, corrosion of metals costs about $276 billion annually. NACE estimates that unmitigated corrosion costs the U.S. economy roughly 3.1 percent of the country’s total GDP. The losses due to corrosion can be divided into 3 categories:
1 - Direct Losses
Waste of energy and materials
2 - Indirect Losses
Shutdown, loss of product
High maintenance costs
Loss of efficiency
3 - Environmental Impact
How and Why does Corrosion Occur?
Common structural metals(such as steels) are produced from minerals(iron ores), which require a large amount of energy to produce. So these metals are in a high energy state and have a tendency to corrode. Certain environments offer opportunities for these metals to recombine and revert to their lower energy states. Thus, corrosion can be described as “extractive metallurgy in reverse”.
The Electrochemical Principle of Corrosion
Corrosion involves both oxidation(anodic) and reduction(cathodic) reactions. The anodic reaction involves metal dissolution(“corrosion”). The cathodic reaction consumes the electrons(shown in Fig. 1).
3) Differential Temperature Cells(the anode and cathode consist of the same metal and differ only in temperature)
Figure 5: Radiography of corrosion under the resin coating
(b) Capacitive image taken in the air, highlighting the main areas of rusting.
(c) Capacitive image taken through a 5 mm thick insulating polymer foam coating.