Holiday Testing on Aged Coatings: Risky Business or Reliable Practice?

Abstract Dielectric strength refers to the ability of non-conductive materials to resist electrical breakdown under an applied voltage. It is a critical parameter for determining appropriate inspection voltages during holiday testing on pipeline coatings. This study evaluated whether aging or repeated holiday testing compromises the dielectric strength of fusion-bonded epoxy (FBE) and liquid-applied pipeline coatings. Additionally, it compared inspection voltages calculated using a traditional fixed-value approach versus a revised method based on Paschen’s Law. Laboratory-simulated aging procedures were conducted with and without UV exposure to represent both underground service and stockpile conditions. Results showed no significant difference in dielectric strength between newly applied and aged coatings, including both laboratory-aged and field-aged FBE coatings. All tested coatings maintained dielectric strengths of ≥800 V/mil, indicating no increased risk when applying the Paschen-based voltage calculation. These findings challenge common industry concerns surrounding over-inspection and coating degradation, suggesting that the perceived risks of repeated testing and aging effects may be overstated.