Relationship Between Pitting Potential of Carbon Steel with Ratio of HCO3-/Cl- in Alkaline Solution postprint

Abstract: The influence of Cl- concentration and the concentration ratio of HCO3- to Cl- ([HCO3-]/[Cl-]) in NaHCO3+NaCl alkaline solution on the pitting potentials of Q235 carbon steel was studied in a chloride ion concentration range from 0.001 to 0.3 mol/L. It was found that when the Cl- concentration is higher than 0.02 mol/L, good linear relationship exists not only between the pitting potential Eb and [HCO3-]/[Cl-] but also between the meatstable pitting potential Em and [HCO3-]/[Cl-], that is Eb and Em increase linearly with the increase of [HCO3-]/[Cl-]. When the Cl- concentration is lower than 0.02 mol/L, [HCO3-]/[Cl- ] is not linear with Eb and Em, and under these conditions, no micron scale metastable pits can be observed on the steel surface before the occurence of stable pits.