The application of embedded sensors is presently being developed to be a reliable corrosion
sensing technique used for structures protected by organic coatings. Results are presented where
embedded sensors were used to monitor the changes associated with a urethane topcoat-epoxy primer
coating and an alkyd topcoat-alkyd primer coating on steel substrates. The results were used to
demonstrate the ability of the sensors to detect changes at the primer/substrate level that would
otherwise be undetected from measurements made from exterior to the coating. The coating systems
were subjected to an ac-dc-ac accelerated testing condition under constant immersion in NaCl media.
Comparison of results from the ac-dc-ac experiments and results of coating systems subjected to
constant immersion in NaCl media is presented to demonstrate the degradation associated with the
accelerated testing condition. The data obtained from electrochemical impedance spectroscopy and
electrochemical noise method demonstrated that a high-resistant topcoat could mask primer degradation
and corrosion at the primer/substrate interface. Analysis of the impedance data using an equivalent
circuit separated the resistance associated with the different layers of the primer/substrate systems.