IN ARID soils or poorly conducting media the electro-chemical corrosion of iron and steel is usually initiated by some heterogeneity of the environment, such as oxygen concentration cells, variations in acidity, etc. In more homogeneous and conducting media the causation potential of the electrochemical corrosion of iron and steel structures is more often due to differences in potential between elements of the structure itself. Both of these two distinct types of corrosion attack are encountered in soil corrosion of ferrous metals, the controlling type depending upon such factors as aeration, soil resistivity and moisture.1
Among structures subject to the electrochemical corrosion by potential differences in the material itself, are pipe lines in salt and/or marshy soils, condenser coils immersed in aqueous coolants, and others where the environment is conducting and relatively homogenous.
In the “graphitic” corrosion of cast iron the causation potential is the very significant potential between graphite...
