Corrosion behavior of low carbon steels and other non-ferrous metals exposed to a real calcareous soil environment

The corrosion behavior of four uncoated low carbon steels: X52, X60, X65, and X70, and three non-ferrous metals: copper, bronze, and magnesium, buried in a real calcareous soil, after a year of exposure time was studied. Samples were not cathodically protected on gravimetric testing in field conditions. Severe roughness and color changes occurred in metals and surface evidenced the presence of rust and calcareous deposits. Oxide scale was generated when metals were immersed in calcareous soil for nine months. In field conditions, X52 was the most corrosion resistant and X65 the most susceptible to corrosion. At laboratory level, a real calcareous soil tested by electrochemical methods exhibited the same trend, which was ascribed to difference in microstructure and phase distribution in steels. Corrosion enhanced when X65 was exposed to calcareous soil collected in spring (0.031 mm/year) and rainy summer (0.077 mm/year), as rain enhanced ions mobility and corrosion. Non-ferrous coupons suggested that a passivation process occurred as corrosion rates (CRs) decreased (0.0025-0.0052 mm/year) compared with the results of low carbon steels.