Why Voltage Matters for High Voltage Holiday Testing on Steel – The Final Edition

In corrosive environments it is considered essential to produce a continuous protective coating for long term performance. Non continuous films provide opportunities for premature failure of the coating system and substrate degradation through isolated corrosion and undercutting. Elements that cause coatings to become non continuous are commonly known as discontinuities or holidays. As such, holiday testing is the method used to find these discontinuities so they can be located and fixed prior to service. The colloquial rule of thumb throughout the coatings industry for high voltage holiday testing had traditionally been 100 volts per mil of coating (1/1000 inch) as the basis of voltage settings. It was believed 100 volts/mil allowed for the detection of holidays while not posing a risk of damaging the coating. The author’s reviews and recent papers have highlighted the inaccuracies of these previous practices through theoretical and experimental evaluation [1, 2]. The author’s original paper provided the basis for updating and correcting current industry standards for proper voltage settings when high voltage holiday testing [3]. To complete the narrative, this paper presents the final round of results for experimental findings of the required voltages for holiday detection on an extended range of coating film thickness and a review of dielectric strength properties of coating materials and their dependences on material thickness.