In the natural gas development and production, the co-existence of H2S and CO2 would cause serious corrosion of production tubing steels. The electrochemical corrosion behavior of 80S and 80S-3Cr anti-sulfur tubing materials were investigated in H2S/CO2 corrosion environment at different sulfur-containing contents by potentiodynamic polarization scanning and electrochemical impedance spectroscopy. And the following research results were obtained. First, polarization curves of the two materials moved in negative X-axis direction with the increase of sulfur-containing content, the cathode reactions were combined controlled by activation and diffusion processes, and the passivation zones appeared in the anode branches of polarization curves when the Na2S·9H2O concentration beyond 1.0%. Second, the potential (Ecorr) increases negatively with increasing sulfur-containing content, and the corrosion current density (Jcorr) decreases, and the Jcorr vaule of 80S-3Cr was smaller than the one of 80S under each corresponding testing condition. Third, there existed two time constants including resistance arc in medium-high frequency zone and Warburg impedance in low-frequency zone in sulfur-containing conditions, and characterization of Warburg Abstract: In the natural gas development and production, the co-existence of H2S and CO2 would cause serious corrosion of production tubing. In order to analyze the effects of the sulfur-containing contents on the corrosion resistance of 80S and 80S-3Cr anti-sulfur tubing materials in H2S/CO2 corrosion environment, the electrochemical corrosion behaviors of the two materials were measured by potentiodynamic polarization scanning and electrochemical impedance spectroscopy. The following research results were obtained: (1) the polarization curves of the two materials moved in negative X-axis direction with the increase of sulfur-containing content, and the cathode reactions were combined controlled by activation and diffusion processes. The passivation zones appeared in the anode branches of polarization curves when the Na2S·9H2O concentration beyond 1.0%. (2) The potential (Ecorr) of the two materials increased negatively with increasing sulfur-containing content, the corrosion current density (Jcorr) decreased, and the Jcorr vaule of 80S-3Cr was smaller than the that of 80S under each corresponding testing condition. (3) The Nyquist spectrum had two time-constants including resistance arc in medium-high frequency zone and Warburg impedance in low-frequency zone in sulfur-containing conditions, and the characterization of Warburg impedance was more obvious with the increase of the sulfur-containing content. (4) With sulfur-containing content increased, the charge transfer resistance (Rt) increased and Warburg impedance (Zw) decreased. (5) The S element content of the first formed corrosion product on the substrate surface was higher, and the 80S-3Cr corrosion product had a lower S element content compared with 80S. In conclusion, one layer of protective iron sulfide products preferably formed the metal surface in H2S and CO2 co-existence corrosion environment which would inhibit corrosion of metal materials, and meanwhile 80S-3Cr material possessed the better H2S/CO2 corrosion resistance than 80S material.
