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Corrosion rates are influenced by the formation of inhibitor aggregates at the steel surface. In situ atomic force microscopy (AFM) was used to investigate the adsorbed structures of cationic surfactant 1-dodecylpyridinium chloride (DPC) at a carbon steel surface in relation to its performance as a CO2-corrosion inhibitor. An increase in the water contact-angle in the presence of DPC indicated its adsorption at the steel, and in situ AFM visualization confirmed the formation of DPC aggregates. The aggregates changed from hemispherical to cylindrical shape with increasing DPC concentration in CO2-saturated brine, resulting in a decrease in corrosion rates as determined by electrochemical measurements. For comparison to the aggressive CO2 environment, the inhibition behavior of DPC was monitored in less corrosive N2-saturated solutions. Formation of cylindrical aggregates was quicker, and a lower corrosion rate was observed in brine saturated with N2 compared to CO2.

The inhibition performance of thiobenzamide (TB) against the under-deposit corrosion of carbon steel in CO2-saturated, chloride-containing environment has been investigated. TB concentrations were varied from 10 – 200 ppm and temperatures from 30°C to 60°C were tested. TB effectively inhibits corrosion at carbon steel surfaces with and without sand deposits, reducing the general corrosion rates below 0.1 mm y−1 in all cases studied. Electrochemical test results suggest that inhibition occurs via adsorption at the steel surface through the S atom of the TB molecule. Potentiodynamic polarization measurements show that the inhibition mechanism differs at surfaces with and without sand deposits with temperature change over the range of 30°C to 60°C. Surface analysis of the corroded steels showed that general corrosion takes place at surfaces without sand deposits, whereas localized corrosion proceeds at the surfaces underneath a sand deposit, both in the presence and absence of thiobenzamide.

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