Effects of chloride content on CO2 corrosion of carbon steel in simulated oil and gas well environments

• Maximum CO2 corrosion rate is reached with increasing Cl− content.
• Cl− can destroy the corrosion product films.
• High amounts of Cl− content can inhibit the cathodic reaction in CO2 corrosion.
• Mass transfer control becomes more efficient as the Cl− content increases.
• Cl− has no effect on the composition of the corrosion product.

Effects of chloride content on CO2 corrosion of carbon steel have been studied by immersion tests and electrochemical measurements combined with scanning electron microscopy, X-ray diffraction and analysis of polarization curves. Results show that maximum CO2 corrosion rate is reached with increasing Cl− content at a constant temperature and partial pressure. CO2 corrosion is a mixed-controlled process, i.e., both activation and mass-transfer steps with increasing Cl− content. Increasing Cl− content can reduce CO2 solubility. Moreover, Cl− can destroy corrosion product films and change morphology of corrosion product films, but it has no effect on the composition of the corrosion product.