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 of 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 a 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 microscopy (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.
Keywords: CO2 corrosion, carbon steel, linear polarization resistance, potentiodynamic sweep, localized
corrosion, chloride, high salt concentration, pitting attack