What Does Holiday Detection Mean?
Holiday detection is the non-destructive process of discovering, finding, identifying or noticing the presence or existence of pinholes, voids, porosity, incompletely coated or other small skipped or missed areas of non-conductive paint film or coating on conductive substrates. Standard methods for holiday testing are defined in ASTM D 5162, ASTM D 4787 and NACE RP0188-90.
Holiday detection allows the discovery of even the smallest coating flaws invisible to the unaided eye. There are various techniques and equipment available for holiday detection.
Corrosionpedia Explains Holiday Detection
Holiday detection allows the discovery of discontinuities in non-conductive protective coatings that could cause premature corrosion without timely corrective measures.
These coating discontinuities or flaws, which allow current to pass through or expose the substrate to corrosive substances or environments, include but are not limited to: runs and sags, cracks, cissing, cratering, undercoating, overcoating, voids, pinholes, contaminants or inclusion in the coating film. Holidays are not easily visible and some, like coating holidays on buried pipes or inside large process tanks, aren't visible during a visual inspection. However, there are now various methods and testing equipment available to detect them.
The two main types of holiday detectors are the following:
- Low-voltage / wet sponge holiday testers, which are used when the coating or dry film thickness is less than 500 microns (20 mils).
- High-voltage holiday testers, which are used when the coating thickness is more than 20 mils.
Holiday detection is important to check as soon as each applied coating has been fully cured. Electrical holiday inspection after each coating allows for the necessary repairs before the final project completion.