Corrosion behavior of nickel-based 718 alloy determined by in situ electrochemical methods at different partial pressures of H2S in 25 wt% NaCl solution at 150 °C

Abstract

The corrosion behavior of nickel-based 718 alloy at seven partial pressures of H2S $$\left( {P_{{{\text{H}}_{2} {\text{S}}}} } \right)$$ was investigated using electrochemical impedance spectroscopy (EIS) and polarization methods in 25 wt% NaCl solution at 150 °C for 168 h. The tested results show that anodic reactions are controlled alternately by the diffusion mostly, then both charge transfer and diffusion and finally charge transfer mainly with the increment of $$P_{{{\text{H}}_{2} {\text{S}}}}$$ . The corrosive products are composed of sulfides and oxides of Ni, Cr and Fe with double layers for $$P_{{{\text{H}}_{2} {\text{S}}}}$$ of 5.1 and 13.0 MPa and three layers for $$P_{{{\text{H}}_{2} {\text{S}}}}$$ of 10.4 MPa according to microstructures and compositions of corrosion products characterized by the scanning electron microscope (SEM) and electron probe microanalysis (EPMA) methods. The inner oxides layer plays a critical role in anti-corrosion in a wet H2S environment at high temperature and pressure.