A review of impedance plot methods used for corrosion performance analysis of painted metals

Modern impedance measuring instrumentation has made testing and data acquisition of the corrosion degradation behaviour of painted metal systems a relatively simple matter, compared to methods used in past decades. However, the analysis of such data is not so simple and requires considerable future work input. This paper reviews some of the various methods available for impedance analysis and discusses their applicability to painted metals. A small library of Bode and Nyquist plot shapes is presented, based on increasingly more complex equivalent electrical circuit models, along with methods for obtaining equivalent circuit component values. Other plotting methods are also reviewed, as well as limitations of impedance plot methods for painted metals.