Effects of hydrostatic pressure and pH on the corrosion behavior of 2205 duplex stainless steel
By Kan, Bo; Wu, Weijie; Yang, Zixuan; Zhang, Xuewei; Li, Jinxu
Published in Journal of Electroanalytical Chemistry
2021
Abstract
The pipeline steels used in deep sea environments are usually exposed to rigorous corrosion conditions such as high hydrostatic pressure (HP) and low pH induced by the potential pitting. In this study, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization methods were employed to study the effect of HP and pH on the corrosion behavior of 2205 duplex stainless steel (DSS) in 3.5 wt% NaCl solution. In addition, in order to determine the optimal cathodic protection potential, EIS was carried out under different cathodic potentials at different HPs. The results indicate that increasing the HP increases free corrosion current density and decreases the free corrosion potential. EIS results also show that HP decreases the impedance of the surface oxide film. At the high HP of 10 MPa, Fe3O4 appears on the surface oxide film, and the proportion of Cr2O3 decreases, accompanied by increases in the proportions of zero-valent Fe and Cr, compared to those at 0.1 MPa. It indicates that the lower compactness and the compositional change in the oxide film at a high HP are the reasons for the decrease in the corrosion resistance of 2205 DSS. Moreover, because HP promotes the hydrogen evolution reaction process, the Tafel chemical desorption process gradually replaces the electrochemical reaction as the control step of the hydrogen evolution process at high HPs. The reasonable cathodic protection potential shifts in the positive direction with the increase in HP. Under the HPs of 0.1, 5, and 10 MPa, the optimal cathodic protection potentials are −0.9, −0.8, and −0.7 VAg/AgCl, respectively.