Testing Coating Porosity using an Elcometer Continuous DC High Voltage Holiday Detector
When it comes to testing the porosity of protective coatings on pipelines, ballast tanks, or bridges for example - or testing for flaws in coatings on concrete - typically the high voltage or holiday detection method is used.
The high voltage Continuous DC method is typically used to test the porosity of non-conductive coatings up to 7.5mm (300mils) thick on conductive substrates.
Elcometer has two Continuous DC detectors: the Elcometer 236, and the Elcometer 266 - and regardless of which one you are using, both gauges give you full control over the voltage and sensitivity settings.
Setting the correct voltage is vital, as testing with a voltage that is too low could fail to break down the gap between the probe and substrate, missing flaws. While testing with a voltage that’s too high could break down and damage the coating, causing the unit to alarm when there are no flaws, while creating a flaw in the process. Testing with bright blue sparks is a clear sign the voltage is too high, and is probably damaging the coating.
The voltage you should use is dependent on the dielectric strength and thickness of the coating being tested, and/or the test method or standard you’re working to. The instruction books for the Elcometer 236 and Elcometer 266 both include an in-depth guide for working out your ideal test voltage based on your coating thickness and the dielectric strength of air. If you are working to a specific test method or standard, there are also simple look up tables for you to follow.