Effect of Environmental Variables on Localized Corrosion of Carbon Steel

Environmental conditions under which localized corrosion of carbon steel could take place in simulated groundwater were examined. Using specimens with crevices, it was determined that at potentials above the repassivation potential, the ratio of the chloride concentration to the total carbonate concentration, solution pH, and solution temperature played critical roles in establishing conditions that promote localized corrosion, as well as in influencing the rate of propagation. Preoxidation in air at 200°C for short times improved the resistance to localized corrosion, but was detrimental for longer times. Monitoring of the open-circuit potential of samples with crevices in air-saturated, alkaline (pH 11) solutions revealed that the repassivation potential could be exceeded and localized corrosion can occur under free corrosion conditions. Factors important to the use of carbon steel as a construction material for high-level radioactive waste disposal containers were discussed.