Corrosion of Buried Metals: Soil Texture and Pore Fluid Saturation

Abstract

The corrosion of buried metals affects geosystems that range from pipelines and nuclear waste disposal to reinforced concrete and archeology. Associated costs exceed 1 trillion dollars per year worldwide, yet current classification methods for soil corrosivity have limited predictive capacity. This study -triggered by the recent development of the Revised Soil Classification System RSCS- seeks to identify the critical soil and environment properties that can improve the prediction of buried metal corrosion. The experimental studies conducted as part of this research recognize the inherently electro-chemo-transport coupled nature of buried metal corrosion, and places emphasis on phenomena that have been inadequately captured in previous studies, such as the effect of soil texture and fines plasticity, partial saturation and moisture cycles, and conditions in Sabkha environments. The comprehensive experimental program involves detailed protocols for specimen preparation, advanced visualization (X-ray micro-CT), corrosion residual characterization (XRD), and detailed image analyses of extracted coupons. Experiments include both laboratory mixtures and a wide range of field specimens gathered throughout Saudi Arabia; furthermore, field observations expand soil assessment to native environmental conditions. Theoretical analyses based on mass conservation and electrochemical phenomena complement the experimental study. Experimental and analytical results lead to new soil corrosivity assessment guidelines. Results show the relevance of the sediment pore fluid saturation, sediment texture, air and water connectivity, active corroding areas, the effect of environmental cycles on buried metal corrosion and evolving backfill contamination.