Premature pipeline corrosion is usually, but not always, due to the failure of the protective coating. A major cause is the presence of flaws in the finished coating, which are collectively referred to as porosity or holidays.
The Elcometer266DC Holiday Detector detects flaws in non-conductive coatings applied to conductive substrates. Voltage is set so that, if the coating is electrically weak in an area, there is sufficient voltage to breakdown the gap between the high voltage probe and the conductive substrate.
As soon as this breakdown occurs and current starts to flow from the probe the test at that specific area of the coating is over and a flaw has been detected. As the high voltage probe is moved over a good area of the coating the high voltage is
re-established and the testing process recommences.

Safety

The probe handle contains the electonics for the high voltage generation and the 266 handle has special ribbing to protect the operator from the high voltage with a dual safety switch to ensure that when the handle is not gripped the test voltage cannot be generated. This ribbing meets the requirements of EN61010, Safety Requirements for Electrical Equipment for Measurement.
The test voltage is selected with reference to the thickness of the coating. The voltage has to be at least sufficient to breakdown the air gap between the probe and the metal substrate.
The menu operation of the Elcometer 266 includes an integrated voltage calculator that relates the coating thickness through the particular testing method to the test voltage.
There is also an internal ‘jeep’ tester that measures the high voltage output and ensures that the test voltage is always delivered by the internal power supply. This means that there is no need for an external voltmeter or ‘jeep’ tester.
If a coating contains a conductive pigment, such as carbon black, or if the coating has a structure that allows it to carry an electrical charge, then a small current will flow from the high voltage probe as it passes over the coating. This current is not the result of flaws in the coating so it can be ignored. The sensitivity of the current detection can be set so that the alarm does not sound until a true flaw is found.
The Elcometer266 has a rechargeable battery pack that can be charged both inside and outside the unit, so two battery packs can be used to keep the unit in service continuously, with each battery pack providing up to 40 hours of power.
The internal speaker emits a ticking sound to indicate that there is high voltage at the handle and a loud audible alarm is activated when a spark is generated at a flaw. The volume of this audible alarm is adjustable so it can be heard in noisy environments.
The new DC High Voltage Spark Tester from Elcometer provides a safe and reliable coatings tester that is easy to use on pipeline coatings and for any coating where flaw detection is specified. New design features make the Elcometer266 a powerful inspection tool that helps to ensure that coatings achieve their specified service life.

John Fletcher is Technical Support Manager with Elcometer Instruments Limited, Manchester, England. www.elcometer.com