Holiday detection looks for discontinuities in a coating barrier on a conductive substrate using a defined electrical method. Its suitability depends on film thickness, electrical properties and access. Applying a test merely because the surface is painted can damage the film or produce misleading indications. [1]
Identify the internal coating system, cure state, intended oil contact and approved inspection method. Confirm the instrument’s applicable range for the actual film and substrate. This article supplies no test voltage or wetting-fluid recipe.
Choose the method from the material boundary
| Condition | Question before testing | Evidence |
|---|---|---|
| Electrically insulating film | Does the selected method cover its thickness? | Coating/instrument guidance |
| Conductive or partly conductive film | Will the intact film itself carry current? | System-specific test suitability |
| Thin internal layer | Could the selected stress damage it? | Qualified inspection condition |
| Edges and attachments | Can probe contact reach the intended area? | Coverage map and geometry |
Resolve indications locally
Mark every indication and compare it with visual evidence, substrate contact and repeatability under the approved method. An edge contact or exposed intentional metal can produce a signal unlike a pinhole in a required coating area.
Record unexamined zones and false-indication mechanisms. Repeating a method beyond its material capability does not make the coverage valid. After repair, inspect the final state with the qualified procedure and tie it to the marked location.
Report film thickness with its measurement method and substrate geometry; one nominal reading does not establish coverage of a curved or inaccessible region. [2]
Report demonstrated holiday-test coverage
Assume 30 m² requires film-continuity assessment, but geometry permits a demonstrated electrical method on only 27 m². The unresolved 3 m² is 10% of the required boundary. Obtain appropriate alternative evidence for those identified regions; no indications on accessible surfaces do not establish full coverage, cure or oil compatibility.
References
- ISO, ISO 29601:2011, Paints and varnishes — Corrosion protection by protective paint systems — Assessment of porosity in a dry film.
- ISO, ISO 2808:2019, Paints and varnishes — Determination of film thickness.