Why Corrosion?

A very valid question to ask is why asset corrosion has any significance. The answer is that the effects of corrosion are far-reaching and impact many aspects of life.

Some of the Effects of Corrosion include:

  • Economic
    • Direct costs of material losses attributable to the wasting away (corrosion) of piping, tanks, ships' hulls, etc
    • Consequential costs due to loss of products or production
  • Conservation of resources
    • Replacement of corroded items indicates a duplication of the use of material and human resources in the design and production of replacements
  • Environmental
    • Air pollution, carbon dioxide emission and water requirements attributable to the production of steel, contamination by hazardous materials released into the environment

Before we can consider how to prevent corrosion, we need to have a basic understanding of how corrosion works.

The easiest way to understand corrosion is to imagine a battery – along the lines of the work covered in Grade 10. The components of this battery are: two different electrodes, an electrolyte (a salt solution through which current can flow) and an external electric circuit. You may have made a mild salt solution, put in an iron nail and a piece of copper, connected them with piece of cable and a small bulb and noted that electricity flowed through the circuit. Effectively, you modelled the corrosion reaction! It is not difficult to understand that by removing any one of the four components from the system, no current will flow.

So it is with corrosion. All corrosion processes require the presence of “cells” comprising two electrodes (called anodes and cathodes), an external circuit and an electrolyte. Removal or modification of any ONE of these components will result in a reduction or cessation in the corrosion reaction rate.

Perhaps you are wondering how a single structure can have two electrodes? At any moment in time, some areas of the metallic surface are at slightly different potentials to each other. The more positive areas are called anodic and the more negative regions are called cathodic.

Sources of corrosion cells on on buried and submerged structures (including pipelines)may include: differential aeration, water table, chemical pollution/contamination and external electric fields.