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Holiday Detector Instruments Buying Guide
Pinhole detection instruments measure the coating for defects on steel surfaces and can prevent premature coating failure.
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DEFELSKO® HIGH VOLTAGE HOLIDAY DETECTOR |
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DEFELSKO® POSITEST LPD LOW VOLTAGE PINHOLE DETECTOR, BASIC KIT |
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DEFELSKO® POSITEST LPD LOW VOLTAGE PINHOLE DETECTOR, COMPLETE KIT |
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BLASTONE DC HOLIDAY DETECTOR 20KV W/ HIGH VOLTAGE HANDLE |
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ELCOMETER® 266 DC HOLIDAY DETECTOR, CERTIFIED |
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ELCOMETER® 280 PULSED DC HOLIDAY DETECTOR INSPECTION KIT |
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| DEFELSKO® HIGH VOLTAGE HOLIDAY DETECTOR | DEFELSKO® POSITEST LPD LOW VOLTAGE PINHOLE DETECTOR, BASIC KIT | DEFELSKO® POSITEST LPD LOW VOLTAGE PINHOLE DETECTOR, COMPLETE KIT | BLASTONE DC HOLIDAY DETECTOR 20KV INCLUDING HIGH VOLTAGE HANDLE | ELCOMETER® 266 DC HOLIDAY DETECTOR, CERTIFIED | ELCOMETER® 280 PULSED DC HOLIDAY DETECTOR INSPECTION KIT | |
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5 Rules of Thumb for using Holiday Detectors on Steel Surface Coatings
Recently we had a customer who was unsure if the holiday detection equipment they had on site would work for their project. This is an important consideration, because if you use a high voltage detector on a thin coating, you will destroy it. And if you use a low voltage on a high-build coating, you won’t get the correct results.
First off, what’s a HOLIDAY?
Holidays are tiny pinhole-sized exposures in the coating. They often form from solvent entrapment. When coating bubbles burst they expose the steel. They may be small, but they create a corrosion cell, which will compromise the integrity of the coating system and become the cause of premature coating failure.
A Holiday Detector uses electricity grounded through to the underlying steel substrate. You run the tool over the coated surface and it will find where these little pinholes are hiding by completing the electric circuit and sounding an alarm.
So here are 5 rules of thumb to help you on your projects.
- For steel coatings with a DFT less than 20mils or 500 microns, you’d use a Low Voltage detector. These emit direct current between 5-90 volts.
- For coatings thicker than 20 mils or 500 microns, the high voltage method is recommended. These emit thousands to tens of thousands of volts.
- As mentioned, the electricity generated by these detectors is conducted via the steel substrate. However, a zinc rich primer is also an excellent conductor and gives false results. If your project uses a zinc primer, the detector is reliable only if the top-coat is non-conductive.
- Retained solvents can also give false results when testing for continuity issues and so it’s vital to make sure the coating system is fully cured before running any form of holiday detection.
And finally… a note on safety
5. It’s important before conducting holiday testing in areas where flammable vapors may be present, to thoroughly check (and if necessary, purge) the atmosphere to prevent the holiday detector from becoming an ignition source.
Why use a Holiday (Pinhole) Detector?
A pinhole detector checks coatings by means of electrical voltage. Microscopically small defects (>20µm) can be detected in the coating of a surface by using a holiday (pinhole) detector. These defects in surface coatings can have extremely large consequences for coating life. The more aggressive the environment the higher the risk that a pinhole will initiate corrosion.
The other application for pinhole detection is where the contents of a vessel or pipeline need protection from coming in contact with the material the vessel / pipeline is manufactured from e.g. food processing plant. They are operated by moving a conductive probe over the surface of a cured coating. These probes can take a variety of forms brass brush, rolling spring, wet sponge.
Common issues with holiday detectors
- The biggest problem with holiday detection systems is selecting an incorrect voltage level. Too high a voltage and you risk burning the coating. Too low a voltage and you won’t pick-up potentially dangerous pinholes.
- Some pinhole detectors are more ergonomically designed others. Earlier designs of pinhole detection operated from a battery suspended from the operators belt. Modern high voltage holiday detectors have a suspension harness to evenly spread out the load on the operator.
Important considerations when choosing the right holiday (pinhole) detector
- The main consideration for when purchasing what voltage type unit to purchase – high or low. The high voltage units are slightly more common.
- Second consideration is ergonomics – the operator is likely to be holding the unit for several hours at a time – how easy is it hold?
- Third consideration is simplicity of operation – it is a fairly simple task, the unit shouldn’t make the process more complicated than it needs to be.
Frequently Asked Questions
How do I know what voltage to set the pinhole detector to?
By and large the most frequent source of information for the voltage is the coating manufacturer. It is important to follow these accurately – too high a voltage and you can damage the coating, too low a voltage and you can miss substandard areas. Sometimes a facility owner or third party inspector can also specify voltage settings. A third source of voltage setting specifications is coating inspection standards. Many of these will detail recommended voltage settings.
What voltages are available?
Low voltage operate from 9 to 90 volts. High voltage units operate from 0.5 to 35 kilovolts.
Do holiday detectors require regular calibration?
Earlier designs of pinhole detection required regular checking with a separate crest meter to check for voltage output. The current design has a crest meter built in that displays and controls the voltage at the electrode.
What type of electrodes are available?
For high voltage use, the most commonly used is a flat wire brush, also available are: rolling springs for pipe exteriors, fan brushes for hard to reach areas and conductive rubber probes to prevent scratches. Low voltage detectors use a wet sponge. These are available in rectangular and round pads and rollers (similar to paint rollers). Sponge sheets are also available to cut your own custom shapes.
