Corrosão de aços utilizados na indústria de petróleo por CO2 sob pressão, temperatura e meio corrosivo similar ao encontrado em reservatórios do Pré-sal

• Autor(a) principal: Lopes, Natália Feijó
• Data de Publicação: 2017
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: Biblioteca Digital de Teses e Dissertações da PUC_RS
• Texto Completo: http://tede2.pucrs.br/tede2/handle/tede/7423
• topic: Aços; Corrosão; CO2; Alta Pressão; Pré-sal; ENGENHARIAS

For the oil industry, corrosion in steel is a serious problem, especially when in presence of aqueous environment and in contact with dissolved gases (CO2, H2S and O2). In cases exploration in pre-salt fields, corrosion control is even more critical, because the crude oil is extracted with high salinity and elevated CO2 content at high pressures and temperatures. Therefore, the objective of this work was to study the performance of steels used in wellbore casing (HSLA steels with 0.04% Cr and with 0.31% Cr and a superduplex steel) in a CO2 corrosive environment with a similar chemical composition to the pre-salt reservoirs, at high pressures (15 and 30 MPa) and high temperatures (50ºC and 90ºC). For this, batch corrosion tests, for 7 and 30 days, were performed and the assessment of the corrosion process was made through the characterization of the scales formed on the steel surface. Corrosion rates were determined by mass loss tests, the characterization of the corrosion products was made by FEG/SEM, EDS, XRD and Raman, and the properties of the corrosion products were evaluated by electrochemical measurements of potentiodynamic polarization resistance and electrochemical impedance. In addition, the in-situ corrosion process was carried out at atmospheric pressure and evaluated by means of electrochemical impedance spectroscopy (EIS) in order to compare with the results obtained at high pressures. The scales formed on the steel surface at high pressure are predominantly composed of iron carbonate enriched with calcium as substitutional element in the lattice and the results indicate that the scales that exhibited more protective properties were the ones formed at higher temperature (90°C). There was a significant improvement on the protection character of these scales with the increase of the chromium content, with special emphasis on the high performance of superduplex steel. Comparing EIS analyzes performed on pre-corroded steels with in-situ measurements, the results obtained by the measurements performed using pre-corroded samples were more coherent with the results obtained by the other evaluation methods. However, the in situ EIS measurement can be important to provide complementary information for the understanding of corrosion involving complex systems such as these studied.