Engineering Tool
Holiday Detector Voltage Calculator
Calculate accurate test voltages for pipeline and tank coating inspection per international and Indian standards. Free, instant, no signup required.
NACE SP0188
ISO 29601
AS/NZS 3894.1
IS 14665
SSPC-PA 8
BS 7079
Low & High Voltage
Calculator Inputs
Recommended Test Voltage
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Thickness (mils)
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Thickness (µm)
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Thickness (mm)
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Voltage (kV)
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Standard Reference – Voltage by Coating Thickness
| Thickness | NACE SP0188 LV | NACE SP0188 HV | ISO 29601 | IS 14665 LV | AS/NZS LV |
|---|
Dielectric Strength Reference by Coating Type
| Coating Type | Dielectric (V/mil) | Dielectric (V/µm) | Typical Use |
|---|---|---|---|
| Fusion Bond Epoxy (FBE) | 125 – 150 | 4.9 – 5.9 | Pipelines, API 5L pipe |
| Coal Tar Enamel | 100 – 125 | 3.9 – 4.9 | Buried pipelines, offshore |
| 3LPE / 3LPP | 100 – 140 | 3.9 – 5.5 | Pipelines >90°C service |
| Liquid Epoxy | 100 – 125 | 3.9 – 4.9 | Tanks, internals |
| Rubber Lining | 80 – 100 | 3.1 – 3.9 | Chemical storage tanks |
| Conventional Paint | 100 – 125 | 3.9 – 4.9 | General structures |
| Zinc-Rich Primer | 60 – 80 | 2.4 – 3.1 | Steel protection |
| Polyurethane | 100 – 120 | 3.9 – 4.7 | Marine, offshore |
Thickness Unit Conversions
| Mils (thou) | Microns (µm) | Millimetres (mm) | Inches |
|---|---|---|---|
| 1 mil | 25.4 µm | 0.0254 mm | 0.001 in |
| 10 mils | 254 µm | 0.254 mm | 0.01 in |
| 20 mils | 508 µm | 0.508 mm | 0.02 in |
| 40 mils | 1016 µm | 1.016 mm | 0.04 in |
| — | 1000 µm | 1.000 mm | 0.0394 in |
Frequently Asked Questions
What is a holiday detector?
A holiday detector (also called a pinhole detector or jeep) is an electronic device used to locate discontinuities (holidays) in protective coatings on pipelines, tanks, and other steel structures. These holidays are tiny pinholes or voids that can allow corrosion if not detected and repaired before service.
What is the difference between low voltage and high voltage testing?
Low voltage (wet sponge) testing uses voltages up to about 90 V DC. It is used for thin coatings (typically under 500 µm / 20 mils) and soft coatings where higher voltages could damage the film. High voltage (spark) testing uses voltages from a few hundred to tens of thousands of volts and is used for thicker coatings and pipeline coatings where greater penetrating power is needed.
Which formula does NACE SP0188 use?
NACE SP0188 gives two formulas. For low voltage testing (coatings ≤500 µm / 20 mils): V = 525 × √t, where t is thickness in mils. For high voltage testing: V = 1250 × √t. ISO 29601 and AS/NZS 3894.1 use similar square-root-of-thickness formulas, which produce a voltage proportional to the coating thickness in a way that avoids both under-testing and damaging the coating.
What standard applies in India?
In India, holiday testing for pipelines is governed by IS 14665 (Corrosion Protection of Steel Pipelines) and OISD-135 (Oil Industry Safety Directorate standard for corrosion control). Both largely align with NACE SP0188 principles. For oil and gas pipelines, OISD-135 is mandatory for upstream operations. IS 14665 covers buried pipeline coatings more broadly.
What safety factor should I use?
When using the custom dielectric method, industry practice is to apply a safety factor of 0.8 (80%) of the theoretical breakdown voltage. This avoids inadvertent damage to the coating while still being high enough to reliably detect holidays. Some specifications for high-risk service (offshore, sour gas) use 0.6 to 0.75.
Why does the AS/NZS standard use a different formula?
AS/NZS 3894.1 (Australia and New Zealand) specifies its own slightly modified constants in the square-root formula. The underlying principle is the same as NACE SP0188, but the constants have been adjusted based on local coating practices and empirical data from the Australasian region. Results are typically within 5–10% of NACE values for the same thickness.
Can I use this calculator for tank linings?
Yes. The same voltage calculation principles apply to tank linings. Use the low voltage (wet sponge) method for thin linings and paint coatings, and the high voltage (spark) method for thick rubber linings and heavy-duty coatings. Always confirm with the coating manufacturer and the relevant project specification before testing.
Engineering Disclaimer: This calculator provides voltage estimates based on established industry formulas. Always verify results against the applicable project specification, coating manufacturer's data sheet, and the relevant standard. This tool does not substitute for professional engineering judgement. Whiz Bang Tools accepts no liability for testing outcomes.