Corrosion Caused by Differences in the Electrolyte

Corrosion can occur due to differences in the electrolyte. These differences may be in the soil resistivity, oxygen concentrations, moisture content and various ion concentrations. The variations produce current flow from one location, through the electrolyte, to another portion of the same metallic structure.


Electrolytic corrosion and galvanic corrosion are similar in that corrosion always occurs at the anodic areas. The essential difference between the two is that in the case of electrolytic corrosion, the external man-made current generates the corrosion; in galvanic corrosion, the natural process of corrosion generates the current. There is also a difference in polarity. In an electrolytic cell, the anode is the positive electrode; in a galvanic cell, the anode is the negative electrode.

It has been established that electric current can generate corrosion, corrosion, in turn can generate electric current. As indicated by these phenomena, it is then possible to prevent corrosion by use of electrical current. This, then, is the basis for cathodic protection. When direct current is applied with a polarity which opposes the natural corrosion mechanisms, and with sufficient magnitude to polarize all the cathodic areas up to the open circuit potential of the anodic areas, corrosion is arrested.

The theoretical considerations indicate that the basis for cathodic protection is relatively simple not difficult to understand. However, practical designs for various applications can vary considerably based on the type of structure to be protected and the conditions encountered.

Source:www.bushman.cc/pdf/corrosion_theory.pdf