Methodology for Evaluation Soil Corrosivity in Lab and Full Scale Conditions for Pipelines in Different Regions of Rio de Janeiro

The chemical, physical-chemical and electrochemical properties of a soil characterize its corrosivity, and external factors determine its relative agressivity. Every buried structure is subject to corrosion and the intensity of the process is related to the aggressivity of the soil. Several parameters such as resistivity, pH, water retention capacity and the presence of soluble salts are characteristics that indicate the corrosivity of a soil related to metallic structures. In this work, several experimental techniques have been used to analyze soil samples corrosivity. The samples were collected in different regions of Rio de Janeiro, considering mountain and industrial features. The laboratory tests consisted of chemical, physical-chemical and electrochemical analyses, besides gravimetric testing. The tests were also carried out in full scale conditions. Qualitative and semi-quantitative analyses of the insoluble constituents were performed through X-Ray Fluorescence Spectroscopy (FRX) and the soluble constituents were evaluated quantitatively through aqueous extracts with FRX and the spectrophotometer in the visible range of light. Concerning the physical-chemical parameters, the pH values, redox potential, resistivity vs soil humidity and water retention capacity were determined. In laboratory, carbon steel specimens were exposed to samples of soils with degrees of moisture varying between 5% and 30%. Corrosion potentials were monitored, polarization curves and corrosion rates were obtained in lab and full scale conditions. After 30 days of exposure, surface analyses of the specimens were carried out to determine the morphology of the corrosion process, being possible to identify the presence of pittings in some specific moisture conditions. With these analyses, it was possible to characterize the corrosiveness of these grounds, which will allow their use in studies of cathodic protection parameters in controlled field.