Locating defects and faults

The differences between AC and DC equipment

When the purpose of a coating is to provide protection to a conductive substrate (such as a steel pipeline), it is vital that the coating is complete and free from cracks or pinholes. Several methods are available for testing and locating such faults.

Buckleys manufacture two distinct types of high-voltage coatings test instrument; AC current or DC current. Both have their advantages and strengths as well as drawbacks and considerations. For instance, AC instruments can work without connecting an earth return cable from an uncoated portion of the substrate to the test instrument. This is particularly useful where the item being tested is coated over its entire surface.

AC current cannot be calibrated and controlled to the same level of accuracy as a DC current and environmental conditions have a greater impact on the output than with a DC current though; making it a less suitable proposition where a stable, accurate voltage is required to test consistent coating.

DC instruments require an earth-return connection from the substrate, in order to created a circuit when a fault is detected, but the voltage applied is more controlled and alarm systems can be incorporated in to the instrument to trigger an alert to the user when a fault is located.

The detector unit is used to supply a predetermined volage to a suitable electrode which is passed over the entire coating area. Weak spots, faults and pinholes are located by the completion of an electrical circuit through the defect to the conductive material beneath; triggering the detector unit’s alarm.

DC pinhole/holiday detectors have a wide range of applications across numerous industries; from locating leaks in flat roofs to integrity-testing corrosion resistant coatings on pipelines; from testing cable insulation to locating faults on waterproof bridge-deck coatings.

Buckleys manufacture a wide range of electrodes and accessories for our detectors; designed to make the testing process as effective and as quick as possible. In addition to this, we offer a range of kits which have been created with a specific purpose in mind and include a combination of accessories which are optimised for that application.