Electrochemical impedance spectroscopy (EIS) is a sophisticated measurement technique for obtaining quantitative data on coated substrates. The U.S. Department of the Interior, Bureau of Reclamation (Reclamation) utilizes this method to evaluate coating systems, most notably for immersion and fluctuating immersion service conditions. Coatings serve a vital role in preventing corrosion and preserving Reclamation's capital infrastructure. Examples of ongoing coatings challenges include progressing environmental regulations which prohibit the use of trusted systems such as coal tar enamel. In addition, the Colorado River quagga mussel infestation necessitates the development of durable non-fouling coatings that prevent mussel adhesion. Structural features at Reclamation facilities are characteristically inaccessible and very expensive to re-coat. Therefore, it is most desirable to re-coat using systems which have very low degradation rates in immersion to obtain the longest achievable service life. EIS is one of the tools utilized by Reclamation to evaluate coatings and is particularly useful for those with no or minimal record of service. Steel coupons (3� x 6� x 0.125�) were prepared and coatings applied according to product manufacturer recommendations. The cured coatings were placed in immersion to simulate service conditions and removed regularly to measure dielectric properties by EIS. The data was used to evaluate two important questions:  (1) how does the coating perform as a barrier to water and ion migration, and (2) how do these barrier properties evolve over time, particularly as coating degradation proceeds? Therefore, the results are used to screen coating systems for both good corrosion resistance (high barrier properties) and weathering durability (properties are maintained for long time periods). Data from this experiment now exceeds 5 years.  The prediction or estimation of coating service lifetime using EIS data is also discussed.

Electrochemical impedance spectroscopy (EIS) for the evaluation of coating systems for immersion

246th National Meeting (2013)

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