Abstract
Electrochemical Impedance Spectroscopy (EIS) has maintained a presence in protective coatings laboratories for decades. EIS is valuable in that it captures resistive and capacitive changes to a coating film as it is exposed to the environmental conditions that produce these changes, i.e. degradations. It also assists in ranking coating systems for their anticipated corrosion protection performance, complementing qualitative, visual observations. However, the EIS equipment has lacked the robustness to be a reliable field tool, and a Faraday cage is needed to minimize electromagnetic interferences during data collection.
An important step to reducing EIS measurements to field practice is to demonstrate a usefulness of the application. Facility and project owners of all infrastructure types commonly request the estimation of a coating’s remaining service life. EIS, or some derivation, has the potential to answer these questions.
The Bureau of Reclamation’s Materials Engineering and Research Laboratory has collected EIS data spanning more than five years. Data is organized according to generic polymer composition (i.e. epoxy, vinyl, etc.) and like materials are compared to identify basic trends. This is used as a first step to identify unique EIS signatures for each material’s degradation process. The established lifecycle data is a starting point for inspectors to interpret field EIS data and quantitatively describe the coating condition to owners. The goal is to provide an estimated remaining service life based on this information. The influence of environmental factors, other variables, accuracy, and the logistics of applying this theory for coating life assessment during maintenance inspections are discussed.
