Effect of Chloride on the Pitting Corrosion of Carbon Steel in Alkaline Solutions

The effect of chloride concentration on the passivity breakdown of carbon steel in deaerated pH = 13.5 alkaline solution was investigated. The results show that chloride plays an important role for the pitting corrosion of carbon steel. When NaCl ≤ 1 M , the carbon steel is passive but for 1 M < NaCl < 2 M , the carbon steel transfers from passive to passivity breakdown. When NaCl ≥ 2 M , passive film breakdown occurs and the passivity breakdown potential ( E b ) of carbon steel is linearly-dependent on the logarithm of the chloride activity in the alkaline solution. As predicted by the PDM, the near-normal distribution of E b is well indicated by the near straight line in the cumulative distribution probability. The analysis in this study gives us a method to calculate the E b of carbon steel in alkaline solution and its distribution for any given chloride concentration.