Re-examining the influence of chloride ions on electrochemical CO₂ corrosion of pipeline steels-corrosion of the heat-affected zones (HAZs) of API-X100 steel

This research investigates the corrosion characteristics of simulated heat-affected zones (HAZs) of API X-100 pipeline steels in CO₂-saturated brines of different chloride concentrations. It links the significances of the HAZ microstructure and chloride concentration to the corrosion kinetics and corrosion products. The ferritic HAZs dissolve at almost two times the rate of acicular ferritic and bainitic HAZs. This paper shows that the samples corrode at rates increasing with the chloride concentration to a maximum rate, at a low chloride concentration, beyond which the corrosion rates decrease with increased chloride concentrations. For the base steel, for instance, the corrosion current densities increased from 8.5μA/cm² in 0.02 mol/L to the maximum 22μA/cm² in 0.07 mol/L before they decreased to 10 μA/cm² in 0.1 mol/L. The corrosion products showed an increase with the chloride concentration, from almost 1-3 μm to 25-35 μm in 0.02 and 0.85 mol/L solutions, respectively.