Coating Inspection

  Corrosion Process

The natural corrosion of steel involves the formation of an electrochemical corrosion cell.  This cell is made up of an anode and a cathode, typically at two different sites on the steel component, an electrolyte, and an electrical connection between the anode and cathode. 

The chemical reaction at the steel anode site is the oxidation of the metal, followed generally by oxide or hydroxide formation :

Fe ®   Fe⁺⁺ + 2 e^-                         (1)

Fe⁺⁺ + 2OH^-® Fe(OH)₂                  (2)

At the same time, an electrochemical reaction, generally the reduction of atmospheric oxygen, occurs at the steel cathode site:

½O₂ + H₂O + 2e^- ®  2OH^-             (3)

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