Recommended Test Voltage
Low Voltage — Wet Sponge
For DFT ≤ 500 μm · Per NACE SP0188 / ASTM D5162 Method A
67.5V DC
Typical range: 9 V (thin) to 90 V (max for LV)
High Voltage — DC Spark
For DFT > 500 μm · NACE SP0188 / ISO 29601
1,265V DC
V = 525 × √(DFT in mm), rounded
✓ LOW VOLTAGE METHOD RECOMMENDED
Calculation basis:
HV formula derived from NACE SP0188: V = K × √t, where t is coating thickness in mm and K ≈ 525 for general epoxy coatings. For tank linings, glass flake, and pipeline coatings, manufacturer-specific values may be higher. Always cross-reference with the coating manufacturer's PDS before testing.
Inspector checklist (before testing):
- Coating fully cured (per PDS cure schedule)
- Surface dry and free of conductive contaminants
- Calibrate detector with known voltage source
- Ground connection secure to bare metal
- Travel speed max 0.3 m/s for accurate detection