HIGH SALT CONCENTRATION EFFECTS ON CO2/H2S CORROSION

HIGH SALT CONCENTRATION EFFECTS ON CO₂/H₂S CORROSION

Haitao Fang, Bruce Brown, Srdjan Nešić

Institute for Corrosion and Multiphase Technology

342 West State Street

Ohio University, Athens, Ohio 45701, USA

The general CO₂ corrosion rates of C1018 carbon steel have been measured for NaCl concentrations 3 – 25 wt% at 20ºC, pH 4.0, 5.0 and 6.0. The corrosion process was monitored by linear polarization resistance and potentiodynamic sweeps. AC impedance was used to measure and correct for solution resistance while weight loss was used to verify the corrosion rate magnitude. Experimental results showed that high salt concentrations decreased the general CO₂ corrosion rate significantly and nonlinearly. Potentiodynamic sweep analysis shows that both cathodic and anodic processes were retarded. Flow velocity effects on general CO₂ corrosion rate were minimized due to an increase of salt concentration. No effect on high salt concentration on initiation of localized attack was detected.

A parallel research project was conducted to investigate the high salt concentration effect on H₂S corrosion. The main objective was to study if the high concentration of chloride could initiate localized attack in an H₂S system. Experiments were conducted in a nitrogen purged system with trace amount of H₂S (50 ppm). Weight loss was used to measure corrosion rates. Scanning electron microscope (SEM), energy dispersive X-ray analysis (EDX) and X-ray diffraction (XRD) methods were used to characterize the morphology, composition and phase identity of the corrosion products. Experimental results show that high salt concentration significantly slowed down the reaction rate in H₂S corrosion. Some pitting attack was found both in salt-free and high-salt conditions. Experimental results did not show evidence that chlorides can initiate localized corrosion in H₂S systems.