In a holiday test, what is applied to detect discontinuities?

• A. a test current
• B. a visual inspection
• C. a thermal impulse
• D. a magnetic field

Answer: (A)

Holidays in coatings are voids that interrupt the protective layer, and detecting them relies on electrical testing. In a holiday test, an electrical input is applied to the coating system and the detector monitors current flow. If a holiday is present, the current can pass through the electrolyte at the defect and produce a detectable discharge, signaling the location of the discontinuity. This is why applying a test current is the method used to reveal discontinuities.

Visual inspection might miss hidden defects beneath the coating; a thermal impulse isn’t the standard method for locating holidays in coatings, and a magnetic field approach targets the metal itself rather than coating discontinuities.