Correlation between soil electrical resistivity, polarisation resistance and corrosion of steel

Soil electrical resistivity, polarisation resistance and similar techniques sometimes are used for predicting both the short and the long-term corrosion of metals such as steels in soils. Herein new field data for pipes after 63 years exposure are presented that show poor correlations to electrical resistivity. One of the reasons is that electrical current flow and hence resistivity cannot be a surrogate for the electrolytic ionic diffusion of metal ions in the corrosion process. Also, corrosion in soils largely is governed by differential aeration, facilitated by air-voids at the soil/metal interface. This phenomenon is not considered in conventional electrochemical experiments. The practical implications are discussed.