A project has been initiated with the aim of extending the model to cover the effect of H2S on CO2 corrosion. This report covers one of the main building blocks necessary to complete the mechanistic CO2/H2S corrosion model, namely, electrochemistry of API 5L X65 carbon steel CO2 corrosion in the presence of small amounts of H2S (≤340ppm). The corrosion process monitored by Linear Polarization Resistance (LPR) and Electrochemical Impedance Spectroscopy (EIS) showed a significant decrease in corrosion rate in the presence of H2S due to the metal surface coverage by a sulfide film. This sulfide film was identified as mackinawite by X-ray photoelectron spectroscopy (XPS). Since the experimental results suggested that the mechanism is a retardation of the charge transfer process, the surface coverage was calculated from the corrosion rate. The Langmuir-type adsorption isotherm was successful in modeling the surface coverage by mackinawite in the presence of trace amounts of H2S.

Subject
Electrochemical impedance spectroscopy, Mackinawite, Hydrogen concentration, Corrosion rate, Metal surfaces, Sulfide films, Sodium chloride, Impedance, Sodium chloride solution, Surface analysis, Carbon steel, Immersion, Electrodes
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2005
Association for Materials Protection and Performance (AMPP)
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