This research was focused on the effect of chloride on the initiation of localized corrosion on carbon steel in a CO2 aqueous environment. The investigation was approached using a two-stage experimental design. The first stage was to build a protective FeCO3 layer on the steel surface in an electrolyte with a low concentration of the salt (NaCl or NaClO4) by purging CO2 and adding additional ferric ions for a high initial FeCO3 saturation condition. The second stage was to challenge the FeCO3 layer by adding additional salt (NaCl or NaClO4), where the effects of different salts could be compared. For both stages, linear polarization resistance (LPR) measurement was performed to measure the general corrosion rate during the experiment followed by weight loss measurement for general corrosion rate and optical profilometry measurements for localized corrosion rate after the experiment. In addition, X-ray diffraction (XRD) and scanning electron microscope (SEM) were used to analyze the composition and morphology of the corrosion product layer.

The results showed that localized corrosion was initiated in the experiments that were conducted at 80°C and 0.53 bar pCO2 with a 1.7 molar (10 wt. %) NaCl. However, almost identical results were obtained when using NaClO4 with the same ionic strength as NaCl. This indicated that changing the ionic strength of the solution, which led to the change of the solubility of iron carbonate, was the key to initiate localized corrosion, rather than the specific type of anion used.

Subject
Steel surfaces, Corrosion rate, Iron carbonate, Saturation, Sodium chloride, Corrosion initiation, Surface morphology, General corrosion rate, Sodium chloride solution, Surface layers, Pitting, Corrosion protection, Localized corrosion
Keywords:
pitting corrosion, CO2 corrosion, sodium chloride, sodium perchlorate, ionic strength, iron carbonate
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2014
Association for Materials Protection and Performance (AMPP)
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