Impact of Fe₃O₄ on the Performance of an Imidazolinium-Based Inhibitor for Mitigation of CO₂ Corrosion of Carbon Steel

Use of corrosion inhibitors to mitigate pipeline corrosion is common in the oil and gas industry. Despite this, few studies focus on how the presence of corrosion products affect their performance. This work aimed to understand the impact of Fe₃O₄ on the performance of a commercial primarily imidazolinium-based corrosion inhibitor formulation. A magnetite layer was formed in an autoclave at a high temperature (1 wt.% NaCl, N₂ sparged, pH 4, 120°C). The performance of the corrosion inhibitor was investigated with and without the presence of Fe₃O₄ (5 wt.% NaCl, CO₂, pH 4.5, 55°C). Linear polarization resistance (LPR) and potentiodynamic polarization were employed to study the effect of Fe₃O₄ on corrosion rate (CR) and inhibition efficiency (IE). Scanning electron microscopy (SEM) and Raman spectroscopy were used to characterize specimen surfaces. The acquired data showed that the presence of magnetite limited inhibitor performance. Dissolution of the magnetite layer over time in the CO₂ environment was also observed. This behavior was expected as the experiments were performed in non-thermodynamically favorable conditions for magnetite formation. Polarization sweeps indicated that the cathodic charge transfer and the limiting current of the H⁺ reduction reaction were significantly accelerated due to the Fe₃O₄ layer. This behavior can be explained by the increase in cathodic reaction area due to the conductive nature of magnetite.