Methodology for evaluation of soil corrosiveness in buried pipelines for different regions of Rio de Janeiro

摘要

Buried structures are subject to corrosion processes, which intensity is related to the severity of the soil. The physical-chemical and biological properties of the soil characterize their specific severity, and external factors determine their relative severity. As external factors, it is possible to mention potential leakage currents generated by cathodic protection and direct current traction systems. Local properties, such as resistivity, pH, water retention capacity and the presence of soluble salts are features that indicate the specific severity of a soil with relation to the metallic structures. In this paper, several experimental techniques were used for evaluation soil corrosivity from 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. Qualitative and semi-quantitative analyses of the insoluble constituents were carried out 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, resistivity versus degree of moisture and water retention capacity were determined. Carbon steel specimens were exposed to samples of soils with degrees of moistures varying between 5% and 30%, corrosion potentials were monitored and polarization curves were obtained. The corrosion rates were also determined under these same moisture conditions. After 30 days of exposure, surface analyses of the specimens were carried out to determine the morphology of the corrosion process and it is 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. Numerical simulation was carried out in order to determine the potential distribution in a cathodic protection system in this soil, considering the experimental parameters obtained.