Electrochemical behaviour of Ni-base alloys exposed under oil/gas field environments

Abstract The electrochemical behaviour of Ni-base alloys (Inconel 625, Inconel 718, G3 and Incoloy 825) is carried out at 80 °C in CO 2 /H 2 S corrosion environments using cyclic potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS) techniques. The passivity mechanisms are analysed and discussed. In addition, some significant characterisation parameters such as E corr , I pass , E pit , E pp , Δ E and I pass in cyclic polarisation curves are analysed and compared to reveal the corrosion resistance of various Ni-base alloys. The equivalent circuit model and ZsimpWin software are utilised to discuss the Nyquist plots of various Ni-base alloys. The diffusion mechanism in EIS measurement is discussed. The result shows that the corrosion resistance of the Ni-base alloys to CO 2 corrosion or CO 2 /H 2 S corrosion follows the sequence: Inconel 625 > G3 > Inconel 718 > Incoloy 825. H 2 S works as a cathodic depolariser with accelerating initiation of the corrosion process.