The role of temperature and H2S (thiosulfate) on the corrosion products of API X65 carbon steel exposed to sweet environment

Abstract

Abstract Oil and gas industry is constantly facing challenges in prospecting and transport, dealing with the corrosion and degradation of the pipelines. This work presents an electrochemical evaluation of API X65 steel exposed to CO2/thiosulfate (10−3mol/l) aqueous deaerated medium. Sweet and sour corrosion were studied simultaneously. Electrochemical Impedance Spectroscopy (EIS) and Linear Polarization Resistance (LPR) tests were performed using an autoclave, 5\u202fbar of CO2 partial pressure at 25, 90 and 120\u202f°C with and without H2S. Corrosion products were characterized by Weight loss, Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD). Protective corrosion conditions were achieved at 120\u202f°C with and without H2S. Without H2S, a stable and denser FeCO3 film was formed. With H2S, FeS film reduced the CO2 corrosive effect and retarded FeCO3 precipitation. Both cases demonstrated an improvement of the substrate corrosion resistance at 120\u202f°C. At this temperature occurred a competitive films formation, reflecting in a corrosion rate decrease.