Investigation of corrosion behaviour of carbon steel in simulated soil solution from anodic component of polarisation curve

Marine structures and buried pipelines are constantly exposed to extreme conditions with elements such as temperature variation, soil ion content, dissolved metals, etc posing a continuous threat on the integrity and lifespan of the structures. Quantification of these elements has been limited to studying only a few of the parameters, with the resulting corrosion behaviour not fully understood. The purpose of this study was to investigate the corrosion behaviour of carbon steel in simulated soil solution using the anodic component attained from modelled polarisation curves. The behaviour of the metal/electrolyte interface was studied using non-invasive in-situ electrochemical techniques at OCP. A combination of voltammetry, electrochemical impedance spectroscopy with X-ray diffraction analysis of the mineral layer were utilised. The expression for the anodic component of the current as a function of potential was attained from log|j_a| vs. potential plots. Mathematical modelling of the experimental polarisation curves was done using OriginPro Data Analysis & Graphing Software. Results showed that at OCP, lepidocrocite, carbonated green rust, calcite and aragonite were found as the corrosion process involved anodic and cathodic zones. Voltammetry around OCP (VAOCP) and linear polarisation resistance (LPR) showed the necessity for corrosion protection as the adopted electrochemical system resulted in a progressively corrosive environment. Kinetics and mechanism of the anodic and cathodic process indicated corrosion processes similar to aerated soil conditions.