For evaluating the performance of protective coatings (paints, polymers, or electroplated layers), a specialized Coating Corrosion Test Cell is required. Unlike bare metal testing, coating evaluation focuses on how well a barrier prevents ions and moisture from reaching the substrate, and how the coating-metal interface degrades over time.

The most common setup for coating evaluation is the Flat Electrochemical Cell. This is preferred because coatings are typically applied to flat panels or coupons. (1) Sample Mounting: The coated panel is clamped against the cell body. The "dry" side of the panel is connected to the working electrode lead, while the "wet" coated side is exposed to the electrolyte. (2) Aperture Control: A large O-ring defines the active area (often 10 cm2 for coatings to capture more statistical defects/pores). (3) Symmetry: The counter electrode (often a Platinum mesh or Graphite plate) should be placed parallel to the sample to ensure a uniform current distribution through the resistive coating.

For the testing techniques, there are three types are normally used: (1) Electrochemical Impedance Spectroscopy (EIS): The "Gold Standard" for coatings. It measures the resistance (Rpo) and capacitance (Cc) of the coating. As a coating degrades, its resistance drops as ion pathways form, and its capacitance increases as it absorbs water. (2）Electrochemical Noise (ECN): A non-destructive method that monitors spontaneous fluctuations in current and potential, useful for detecting the very first signs of under-film corrosion or "pitting" through the coating. (3) Cathodic Disbondment: A constant negative potential is applied to a "scribed" (scratched) coating to evaluate how quickly the coating peels away from the defect site.