The electrochemical impedance spectroscopies （EIS） of electrodes made of carbon steel and duplex stainless steel were obviously different in single-phase or two-phase chloride media with different flow volocities. With increasing flow velocity the shear stress on the metal electrode surface and the electrochemical corrosion rate increased, and the electrochemical reaction impedance decreased. Finally the flow induced corrosion rate of metal electrode was increased by the synergism effect. Compared with EIS of carbon steel electrode, it was at higher flowing velocity that the feature of Nyquist plot in low frequency region of duplex stainless steel electrode was changed. All above these proved that Cao＇s EIS theory for irreversible electrode can be used for studying electrode process under flow-induced corrosion. The experimental results showed that it was in low frequency region that the EIS feature of electrode in flowing media was changed when the shear stress on the electrode surface was high enough and that the inductive impedance feature of Nyquist plot in low frequency region meant that the normally dissolving mechanism and rate of metal electrode surface were changed by strong hydrodynamics. At the same time, the local corrosion, pits and holes, occurred on the electrode surface. Under this condition, the EIS of passive electrode further showed that the metal electrode surface was subject to scraping and stroke of solid particles in flowing solid / liquid two-phase media.
Acta Metallurgica Sinica
carbon steel, duplex stainless steel, flowing chloride medium, flow-induced corrosion, electrochemical impedance spectroscopy （EIS）