Coating Service Lifetime Evaluation by Electrochemical Impedance Spectroscopy (EIS)

Project ID: 7673
Principal Investigator: Bobbi Jo Merten
Research Topic: Repair and Maintenance
Funded Fiscal Years: 2013, 2014 and 2015
Keywords: lifetime prediction, coating service life, electrochemical impedance spectroscopy (eis), structural health monitoring (shm)

Research Question

How can electrochemical impedance spectroscopy (EIS) data be utilized to predict estimated service lifetimes for Reclamation specified coatings as well as a method for quantitative EIS field inspection?

Need and Benefit

EIS is a powerful tool for analyzing coatings and other dielectric materials. Most often EIS data is used as a method to rank coating performance. It serves well to do this, especially to complement standard visual analysis. Further interpretation of EIS data is possible; however, many researchers do not attempt this due the extensive training required on the instrument. The principal investigator for this study is a Ph.D. coatings chemist who was fortunate to work with pioneers in EIS coatings research during graduate school.

As our understanding of coatings materials properties, EIS data manipulation, and structural health monitoring (SHM) have evolved, we believe it is time to revisit service lifetime prediction techiniques based on EIS data obtained from the accelerated weathering of coating systems. The extensive library of data at the Bureau of Reclamation is especially unique in that much of it now spans 5 or more years of accelerated weathering.

The field inspection of Reclamation coatings can now be greatly improved by implementing quantitative EIS inspection measurements. This data provides an accurate snapshot of the coating condition and can be used to predict the remaining life. For example, there is a distinct difference between the EIS data of an intact coating on steel and one which has corrosion reactions occuring at the coating/steel interface. Both systems appear identical by a visual inspection, however. In addition to service life prediction, this information would be used to increase the efficiency of inspection schedules.

The overall benefit of this experiment is the capability to specify the highest quality coatings for its water and power infrastructure. This is important given that the majority of our presently specified systems provide half the service life of previously used systems such as coal tar epoxy, lead based paint, and vinyl resins. The recently recoated Flatirons penstocks would be an excellent candidate for EIS field measurements throughout the coatings lifetime, especially since the interior liner is a newly specified coating system. With the proper certification, this inspection method is now available for field application to any Reclamation coating in order to obtain the quantitative data necessary to identify remaining service life.

This development of an EIS database for all Reclamation coating systems could provide tremendous cost reduction to Reclamation as well as other agencies. The long-term benefit is a greater understanding of coatings protection and degradation processes as well as the implementation of a field inspection method for the accurate measurement of the remaining service life of a coating.

Contributing Partners

Contact the Principal Investigator for information about partners.

Research Products

Independent Peer Review

The following documents were reviewed by qualified Bureau of Reclamation employees. The findings were determined to be achieved using valid means.

Re-Evaluating Electrochemical Impedance Spectroscopy for the Field Inspector's Toolbox: A First Approach (interim, PDF, 366KB)
By Dr. Daryl A. Little, Dr. Bobbi Jo Merten, Dr. David S. Tordonato and Dr. Allen D. Skaja
Publication completed on January 13, 2014

Electrochemical Impedance Spectroscopy (EIS) captures resistive and capacitive changes to a coating film as it is exposed to the environmental conditions that produce these changes. It is traditionally a laboratory method; however, this paper describes an approach for applying this method to coated infrastructure. The goal is to provide quantitative coating assessments to improve coating maintenance planning by accurately estimating the remaining useful life.

Bureau of Reclamation Review

The following documents were reviewed by experts in fields relating to this project's study and findings. The results were determined to be achieved using valid means.

Coating Service Lifetime Evaluation by Electrochemical Impedance Spectroscopy (EIS) (final, PDF, 1.1MB)
By Bobbi Jo Merten
Publication completed on September 30, 2015

Commercial protective coatings used on Reclamation structures received nearly ten years of laboratory evaluation through thesophisticated technique of electrochemical impedance spectroscopy (EIS). The research project organized this data and performedcritical evaluations in search of electrical signatures for material degradation, i.e. loss of the coatings protective nature. The result isa quantitative field inspection method that augments our standard, visual inspection methods. The report details the conversion ofthe laboratory EIS technique into a ruggedized field inspection tool; the long-term laboratory studies provide benchmarking for evaluation of these field coating systems. The results include successful demonstrations and recommendations.

The following documents were not reviewed. Statements made in these documents are those of the authors. The findings have not been verified.

Electrochemical Impedance Spectroscopy Coating Evaluation (final, PDF, 1.7MB)
By Bobbi Jo Merten
Publication completed on September 30, 2016

This bulletin summarizes the research results and potential application to Reclamation's mission.

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Last Updated: 4/4/17