Basics of Corrosion
Corrosion is a constant force in industries from Oil & Gas production, Maritime, to construction of highways, bridges, pipelines, & any underground systems. Corrosion is a natural process where refined materials react with their environment, and revert to a more chemically-stable form. The rate of corrosion is dependent on a number of environmental variables, but for corrosion to occur four basic elements are required (Anode, Cathode, Metallic Path, and Electrolyte).
In the fight against corrosion, integrity engineers focus on removing the presence of one or more of these basic elements. The first defense against corrosion is a coating system which helps to protect the asset from the surrounding electrolyte. Coatings are typically used as a barrier coating, protecting the substrate from contact with the Electrolyte. In addition to serving as a barrier, some coatings also use inhibitive, or sacrificial pigments, causing passivation, or a sacrificial anode to form at any Coating Holidays or defects.
Integrity engineers must also utilize cathodic protection (impressed or passive) to protect assets, as coatings can be damaged, which can amplify corrosion locally at the defect (Coating Holiday, cracking, etc.). Cathodic protection systems combat corrosion by converting all of the anodic (active) sites on the metal surface of an asset to cathodic (passive) sites by supplying electrical current (or free electrons) from an alternate source to equalize the potential on the surface of the metal structure (left).