Measurement of carbon dioxide corrosion on carbon steel using electrochemical frequency modulation

Abstract

Electrochemical frequency modulation (EFM), which has been widely used in the research field of semiconductors, was used to study CO2 corrosion on carbon steel under film forming and non-film forming conditions. In the EFM technique two sinusoidal voltage signals of different frequencies are applied to the system and the response current is measured at zero, harmonic and intermodulation frequencies from which the corrosion rate is calculated. The corrosion rate calculation depends upon whether the system is under activation, diffusion or passivation control. In this research rotating cylindrical electrodes made of AISI carbon steel 1018 were immersed in 3% (w/w) NaCl solution saturated with carbon dioxide. The experiment was done at 5 rpm, 24 rpm and 100 rpm simulating laminar, transient and turbulent flow regions respectively. The exposure time was varied from 1 hour to 24 hours and the results were compared with other electrochemical methods such as linear polarization (LP) and electrochemical impedance spectroscopy (EIS). It was found that it was crucial to select the correct EFM model to ensure accurate corrosion rate measurement. A very good agreement in the polarization resistance was obtained between EIS and EFM indicating that EFM can be used as an effective tool in corrosion studies providing that the corrosion mechanism is known.