Electrochemical impedance spectroscopy studies of coated steel specimens in soils

The electrochemical impedance spectra of specimens, cut from an epoxy-coated steel pipeline. in three soils in the Memphis metropolitan area were monitored over a 90-day period. The test soils were carefully selected to reflect the range of soil types found in this region. from the Nyquist and Bode plots generated, (a) the temporal variation of the low-frequency (1 Hz) impedence modulus and phase angle were obtained, and (b) an appropriate equivalent electrical circuit was identified, with it having the following elements R-SOIL (representing the soil resistance), C-COAT (representing the resistance of pores in the coating), C-DL (representing the capitance of the double layer). R-CT (representing the charge-transfer resistance), W-DIFF (representing the Warburg impedance).