Geoelectrical and Physicochemical Evaluation of Soil Corrosivity on Metallic Pipelines: A Case Study

Geoelectrical sounding and physicochemical analyses were conducted on the topsoil underlying Osupa area in Ogbomoso, south western Nigeria to evaluate the soil corrosivity on the metallic water pipelines across the area. Schlumberger electrical resistivity soundings were conducted at 24 stations with electrode spacing varied from 1 to 100 m. The resistivity data were interpreted by using partial curve matching and computer-aided 1D inversion. Physicochemical analyses were also conducted on soil samples collected from about 1 m depth in test pits dug at points coincident with the sounding stations, following the BS/AWWA/ANSI Standards for Corrosivity testing to determine the soil pH, redox potential, moisture content and chloride content. The soil corrosivity was evaluated based on soil resistivity alone and the combined effect of soil pH and resistivity. The studied soils have resistivity ranging from 10 Ωm to 492 Ωm and thickness varying from 0.5 m to 4.6 m. The pH, moisture content, redox potential and chloride content range from 4.22 to 8.41, 14.33% to 29.09%, +50 mV to +97 mV and 102 ppm to 196 ppm respectively. The corrosivity intensity, based on the combined effect of soil pH and resistivity is essentially Medium-to- Medium-High being Medium at 10 locations, Medium-High at 8 locations, and High, Medium-Low, and Low at 2 locations each. More reliable information can be obtained about soil corrosivity toward buried metallic structures if the combined effect of the soil parameters affecting soil corrosion is considered.