Holiday (Continuity) Testing
Holiday (Continuity) Testing is a Non-Destructive Testing method applied on non-conductive protective coatings such as rubberized waterproofing to detect unacceptable discontinuities such as pinholes and voids that are not readily visible.
Discontinuities are detected by the formation of an electrical circuit (current flow to complete the electric circuit) in areas where there is an insufficient coating to resist the flow of electrical charge. If the flow of electrical charge is detected, then the test area is termed as conductive, indicating the presence of discontinuities.
The testing is usually performed on tank interiors, chemical storage vessels and buried structures because of the importance of maintaining adequate coating protection in aggressive service environments.
Application
A holiday (continuity) test is performed with either a low-voltage or a high-voltage holiday detector, which is an electrical device used to determine the location of a gap or a void in the coating. Low-voltage holiday testing is used when the coating system is less than 500 microns (20 mils) thick.
High-voltage holiday testing is used when the coating system is thicker. High-voltage holiday testing requires special care not to damage the coating or cause injury to the operator.
