Find the Holidays Before the Water Does

The Wet Edge, No. 010. Short field notes for coating crews.

A pinhole you can't see is still a hole. In a tank or a clarifier, water will find it, and the corrosion starts underneath where nobody's looking.

That's what a holiday test is for, the same way you pressure-test pipe before you backfill. For coatings under 20 mils, the usual method is the low-voltage wet sponge, at 67.5 or 90 volts, with a little non-ionic wetting agent in the water so it gets into the pinholes. Thicker linings get a high-voltage spark test, with the voltage set by film thickness. NACE SP0188 covers both, and the spec and data sheet set the numbers for your job.

Timing matters. Test after the coating has cured enough per the data sheet, and before the structure goes into service. Test too soon and retained solvent can throw false readings. Too much voltage can damage a good film.

Why it matters: a holiday found today is a dab of repair coating. A holiday found after fill is a drain-down, a blast and a recoat, with the owner watching.

The practical move: mark every hit, repair it per the data sheet, and retest the repairs. Keep the tester's calibration current and log what you tested.

Bottom line

Holiday test every immersion lining after it cures and before it goes in service. Mark it, fix it and retest it while it's still a dab of repair coating.

Further reading: Holiday Testing of High Performance Coatings Explained. Standards: AMPP/NACE SP0188.

Talk to a consultant. Questions on a job? Atlantic Coating Consultants supports contractors in PA, NJ, DE, MD, DC, WV and OH with product recommendations, field support and crew training. Call 484-644-5303 or email atlantic@tnemec.com.