Avaliação do comportamento eletroquímico de três (3) tipos de aços eutetoides em ambientes ricos em NaCl, H2SO4 e CO2

Abstract

The use of tubular components used for the oil transportation and lifting process that interconnect wells on the seabed and ships or platforms on the surface, also known as flexible pipelines, is very common in the Brazilian oil and gas production industry, since the large reserves are found on the sea floor. Therefore, these structures are subjected to adverse environmental conditions, intense operations and exposure to fluids that severely degrade them. Thus, in this work, a comparative evaluation of the electrochemical behavior of three (3) types of pearlitic steels used for the manufacture of these components was carried out. The steels used in this research were manufactured in different ways, have small variations in their chemical composition and were subjected to different heat treatments, all with the aim of improving their performance under operating conditions. To evaluate the corrosion resistance, electrochemical tests were performed (open circuit potential and linear potentiodynamic polarization) using solutions that simulate the exposure conditions during service. The solution containing NaCl simulated sea water and the H2SO4 solution was used due to the presence of sulfur-rich compounds in the petroleum composition. In addition, during the electrochemical tests, CO2 gas was bubbled into each solution, in addition to a temperature different from the environment (80°C) (NaCl, H2SO4 and NaCl-H2SO4 mixture); this gas is present in the fluid produced from the pre-salt in high concentrations, as well as in the injection fluid, used to maintain pressure in the reservoir and this is a temperature used for this procedure. Finally, to obtain oxide layers from the corrosive process, the steel surfaces, after the polarization tests, were analyzed using the Raman spectroscopy characterization technique. In this way, different values of resistance to polarization and also of corrosion products were obtained in the specimens in the electrochemical tests. The wires that presented greater resistance to corrosion in the respective evaluated conditions were: PCE (NaCl+CO2+80°C), PCL (H2SO4+CO2+80°C) and PCL (NaCl+H2SO4 +CO2+80°C). In the characterization technique used, FeCO3 and FeSO4 salts were found, in addition to other oxides resulting from corrosion.