Film stability for the system Fe-Cl--CO2-H2O is characterized by electrochemical methods and surface analysis techniques. Additions of CO2 (g) to API 5L X-52 steel exposed in brine solutions promoted the formation of FeCO3 on active sites left by dissolution of FexOy films under hydrodynamic conditions. When rotating rate is introduced to the steel-electrolyte interface, a competition for the active sites is showed during electrochemical experiments because of the diffusion phenomenon of the ionic species to the surface of the metal interface. These interface interaction creates active local sites, and mechanical detachment of different layers formed at the surface, like FexOy or FeCO3. Amine based inhibitor additions change the nature of the film creating diffusion controlled process and increasing the stability of a new adherent film that increased the capacitance of impedance signal. Electrochemical Impedance Spectroscopy and surface techniques was used for film kinetics characterization for different flow conditions, CO2 and inhibitor addition. A phenomenological description is proposed from transfer function results that include film stabilization in steady state according to active sites of the surface of the corrosion product film and metal.

Subject
Steel surfaces, Corrosion rate, Iron carbonate, Diffusion, Impedance, Acidity, Corrosion products, Sodium chloride solution, Oxide surfaces, Interfaces, Film formation, Surface layers, Steel
Keywords:
Active sites, corrosion assisted by CO2, film growth, impedance signal
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2004
Association for Materials Protection and Performance (AMPP)
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