Holiday testing, also known as continuity testing, is a non-destructive method for detecting pinholes and voids in coatings. It’s commonly used to inspect coatings on pipelines and structures in offshore industries.

Here’s how holiday testing works:

A holiday detector passes a charged electrode over the coating.

If a holiday is present, the current flows from the electrode into the conductive substrate beneath the coating.

The current returns to the detector through a ground wire, completing the circuit and triggering an alarm.

The type of holiday testing used depends on the thickness of the coating:

Low-voltage holiday testing

Used for coatings less than 500 microns (20 mils) thick. This is typically done using the wet sponge method.

High-voltage holiday testing

Used for thicker coatings. This method requires special care to avoid damaging the coating or injuring the operator.

Holiday testing is important because holidays can significantly affect the integrity of a coating.