What Does Holiday Spark Test Mean?
A holiday spark test is a procedure used to check for inconsistencies such as pinholes, discontinuities, holidays and voids in coatings covering metallic surfaces. In a spark test, a voltage is applied across metal fibers temporarily placed on the coated surface. Where holidays exist, the underlying metal surface is accessible and a circuit is created that allows an electric current to flow. This creates a spark and notifies a device or person of the holiday.
Holiday spark tests are particularly important when applying anti-corrosive coatings, because undetected holidays leave the underlying metal prone to corrosion at those locations.
Corrosionpedia Explains Holiday Spark Test
Holiday spark tests work by taking advantage of the electrical conductivity of the metal substrate being protected by the coating. Discontinuities in the coating expose the metal at the surface, allowing conductivity tests to work when they otherwise wouldn’t due to the non-conductive coating.
An important factor is the coating's thickness. A larger voltage is required to detect holidays in thicker coatings. Hence, holiday tests are typically started at a lower voltage and increased to an appropriate value based on the thickness of the coating and the successful detection of a positive control.
High voltage holiday tests are used to test coatings up to 25 mm in thickness. Test devices connect to audible or visual output to inform the tester of the holiday. Although some tests use continuous DC current, pulsed DC tests can be used when the coating is somewhat conductive or the surface is damp or dirty. Naturally, moisture can interfere with the accuracy of the test.
Operators must consider safety hazards before testing because these test produce sparks.