In-situ laboratory testing of pipe coatings was conducted on three steel pipes measuring 2.5 inches (6.35 cm) in outer diameter X 6 feet (183 cm) long that had been buried in Champaign, Illinois soil for the past 14 years. Prior to burial, two of the pipes had been coated with 0.0315 inch (0.8 mm) thick polyethylene sheaths, and intentional coating flaws were introduced by stripping the coating along the length of the pipe to create bare areas measuring 1% and 10% the total pipe surface area, respectively. The third pipe was not coated prior to burial (i.e., 100% bare). The soil was saturated with water, and electrochemical impedance spectroscopy (EIS) was conducted. EIS measurements indicated that the
relative degree of pipe coating degradation can be estimated without digging up the pipe by using a simulated equivalent electrical circuit model.