Bent Bolt

As explained previously, galvanic corrosion occurs when two or more different metals are coupled together and are immersed in a common electrolyte such as sea water. However, we have all seen heavily corroded steel structures with no other metals connected. This type of corrosion occurs due to variations in stress levels placed on the structure which leads to the creation of anodic-cathodic galvanic cells.

For example, when steel is welded or joined, the point of the weld or joint is subjected to huge stress concentrations. The welds become anodic to the surrounding steel and become far more prone to corrosion. The unstressed steel then becomes the cathode and places large demands on the dissolution of the welded anodic areas. This stress also occurs when steel is bent, bashed or mechanically worked.

Similarly, major variations in oxygen concentration will cause anodic and cathodic sites on a single surface of immersed steel. The area with the least oxygen becomes anodic and the area with more oxygen becomes cathodic.