Estudo da corrosão de ligas Fe-Cr-Mo em água artificial de tanque de armazenamento de petróleo saturada com CO2.

Abstract

The objective of this work was to evaluate the influence of the percentage in mass of Mo in Fe-Cr-Mo alloys against CO2 corrosion in artificial water of oil storage tank and to propose an experimental alloy to be used in susceptible to this kind of corrosion pipes. They had been studied the 1020 carbon steel, for comparison, and two types of Fe-Cr-Mo alloys, one advertising, called P9 (Fe-9Cr-1Mo); and one experimental alloy, E (Fe-9Cr-5Mo). They had been made measurements of LSP with time of Eoc of 1 h. The curves had shown that, in 1020 steel, the dissolution of Fe occurs only, whereas, with the increase of the percentage of Mo, occurs passivation. Monitoring of the corrosion was made by electrochemical impedance spectroscopy, throughout 168 h of immersion. Nyquist diagrams had shown that the increase of Mo content increased the impedance of the studied alloys. Although, the Bode representations showed that there is only one process in the corrosion of 1020 steel, while there are two ones for P9 and E alloys. The characterization of the surface was made by SEM. The distribution of the corrosion products was homogeneous in the 1020 steel and heterogeneous one in the other alloys. The identification of the corrosion products was made by RAMAN spectroscopy, showing that there was protective corrosion products formation only to Fe-Cr-Mo alloys and that only the E alloy presented Mo-containing products. This is in agreement with the results obtained in polarization curves and in impedance diagrams, once Mo can stabilizes passivation films. So, experimental E alloy can be used in substitution of P9 alloy in oil exploration plants susceptible to CO2 corrosion.