What is a coating holiday and how is it detected?

• A. A crack in the metal substrate.
• B. A blemish on paint color.
• C. A defect exposing the substrate; detected with holiday detectors and pulse/continuous testing.
• D. A type of rust formation.

Answer: (C)

A coating holiday is a defect where the protective coating is missing or too thin, exposing the underlying metal substrate. That exposed area can allow moisture and electrolytes to reach the metal, increasing the risk of corrosion if not repaired. Detection uses holiday detectors that apply a voltage to the coated surface; the coating acts as an insulator, so normally little current flows. When a holiday is present and the substrate is exposed, current flows and the detector flags the defect. Detection can be done with either pulsed or continuous testing modes to locate and map these defects across the surface.