Influence of Soil Particle Size, Covering Thickness, and pH on Soil Corrosion of Carbon Steel

The effects of environmental factors, such as particle size, covering depth, and pH, on the corrosion behavior of carbon steel in silica sand filled with a 3% NaCl solution were investigated by electrochemical impedance spectroscopy (EIS) and polarization measurements.The corrosion rate initially decreased with the decrease in the oxygen concentration near the steel surface, which was a result of the consumption of the dissolved oxygen during the corrosion reaction. The corrosion rate became constant at approximately 10 μm y−1 regardless of the particle size and covering thickness. At the steady state, both the anodic reaction (iron dissolution) and cathodic reaction (oxygen reduction) appeared to be suppressed by the formation of an oxide film on the steel surface. In the silica sand filled with non-buffer and buffer solutions of pH 3–6, the corrosion rate was initially significantly enhanced by the hydrogen ions (H+). The period of the enhancement depended on the buffering capacity. However, the corrosion rate was subsequently independent of the pH due to the neutralization of the solution in the vicinity of the steel surface.