What is the purpose of a coating system holiday test?

• A. To detect discontinuities in corrosion-resistant coatings by applying a test current to reveal substrate exposure.
• B. To apply a protective coating to extend life.
• C. To measure coating thickness.
• D. To visually inspect for uniformity.

Answer: (A)

Holiday testing for a coating system focuses on finding defects in the protective film by applying a test current or voltage and looking for signs of current flow that reveal where the substrate is exposed. The coating is an insulator, so where there is a holiday (a crack, pinhole, or other discontinuity) the current will bridge to the metal, producing a spark or detectable signal at that spot. This lets inspectors map and quantify defects so they can be repaired, ensuring the coating acts as a continuous barrier against corrosion. Other tasks like simply applying coating, measuring thickness, or visually inspecting for uniformity do not specifically identify these hidden discontinuities and therefore don’t guarantee the same level of protection.