testing | Holiday detection
Above: typical examples of coating defects. From left: pinholes, runs and snags, cratering and cissing
detection of flaws in coating up to 25mm thick. Accord- ing to Elcometer, the device can even measure coatings that are damp, dirty or slightly conductive. The 280 unit is designed to withstand the rigours of
field operation, featuring a rugged shockproof casing complete with waterproof control buttons that are designed to be operated by a gloved-hand. The detector also uses a two-stage safety system; a safety trigger integrated into the handle cuts the high voltage when released to ensure safe operation. In addition, ribbing that extends along the nose cape is said to protect the operator from the risk of spark creep. The unit incorporates a voltage calculator allowing
the test voltage required for the applied coating thickness to be determined using a number of estab- lished test standards. Three indicators draw attention to the presence of a flaw in the coating: a flashing detector display, a bright LED indicator and a user adjustable audible alarm. The Elcometer 280 can be used in accordance with a number of high voltage holiday detection standards, including AS 3894.1, ASTM D5162 and D7487, NACE SP0188, SP0490, TM0186, TM0384 and RP0274, ANSI/ AWWA C203 and C214, and JIS G3491 and G3492. The company says it can also be used with the new ISO standard from the CEN Technical Committee CEN/TC 139/SC 1 Working Group 12 (published in 2011 as ISO 29601 Paints and Varnishes – Corrosion protection by protective paint systems – Assessment of porosity in a dry film).
As the Elcometer 280 operates with a pulsed DC
voltage output, there are significant operational differences from conventional DC high voltage holiday detectors such as the company’s Elcometer 266. Most importantly, the pulsed DC detector can be operated with a trailing signal return cable, so does not need the direct metal-to-metal ground contact that a DC high voltage system requires. The Elcometer 280 generates a pulsed output
voltage so a capacitive signal return is all that is required to ensure any flow of current in the substrate
40 PIPELINE COATING | November 2012
due to a holiday will be maintained and will flow back to the unit to signal an alarm. This is an easier and more practical test set-up in many situations, particularly where the coating process is complete and no access is possible to the uncoated substrate, says Elcometer. The capacitive signal return can also be achieved
using a grounding mat. In this case, a conductive rubber mat is wrapped around the coated pipe and connected to the grounding pin that is driven into the earth and the signal return cable. The circuit is completed when a flaw is detected via the capacitive effect of the area of the conductive mat over the coating. A range of mat sizes is available for pipes from 229mm up to 1,067mm diameter. Pulsed systems are also said to be better able to
withstand slightly conductive paths, which can lead to false alarms with DC systems, as the energy is contained within the very short pulses. The pulsed system can, therefore, maintain the test voltage on a slightly conductive coating and is less easily overloaded. And because the pulsed DC system is looking for a significant release of energy to signify a flaw, a small release of energy to a slightly conductive coating will not trigger an alarm, says Elcometer. The Elcometer 280 is available in two user options.
The Standard Detector package includes a 5m trailing signal return cable, single rechargeable battery pack and universal charger, a rolling spring connection shaft, shoulder strap and calibration certificate. The Top package adds an additional battery pack and an extra 250mm probe extension shaft. Accessories include brush and phosphor bronze
probes for localised testing, right angle brush probes up to 1m for large flat areas, and right angled conductive rubber probes up to 1m for curved surfaces. Circular wire brushes are recommended for internal pipe coating and are available from 38mm to 305mm diameter. C-type wire brushes and complete rolling spring assemblies are available in several sizes for external testing of pipe covering the diameter range from 150 to 1,425mm. ❙
www.elcometer.com
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