Corrosiveness of Brazilian Candiota Coal

Resumo

Candiota city, in the south of Brazil, is located near the largest reserves of mineral coal of the country. This coal is used for thermoelectric power generation. The extraction of coal from open-cut mines involves opera-tions may generate at least some particulate matter into the atmosphere. These particles retained on the sur-face of metallic structures exposed to the atmosphere, may adsorb gases such as CO, CO2, SO2 and NO, which, in combination with humid air form corrosive substances, such as HNO3 and H2SO4. This paper aims to evaluate the influence of Candiota coal on the corrosion of buried steel structures and exposed to atmos-phere containing particulate matter from coal combustion. The coal sample was characterized by SEM (scan-ning electron microscopy), thermogravimetric analysis (TGA), surface area analysis (BET method), electrical conductivity (EC) analysis, FTIR and Raman spectroscopy. Corrosion was simulated by exposure of steel samples to coal particles and thermoelectric industrial atmosphere. Electrochemical tests of solutions leached from the coal were conducted by voltammetry to evaluate the soluble compounds corrosiveness. The corro-sion rate was determining following the technical standard ASTM G1-90. Localized attacks and corrosion products formations were detected in API 5L Grade B steel exposure to coal. The average corrosion rate for the samples in direct contact to the pulverized coal was 0.15 mm/year, while in samples exposed to the at-mosphere from industrial power plant was 0.30 mm/year. It is concluded that API 5L Grade B steel metal structures, exposed to atmospheres rich in Candiota coal and its derivatives, must be properly protected and monitored to avoid future damage caused by corrosion.