Holiday testing is a non-destructive test method applied on protective coatings to detect unacceptable discontinuities such as pinholes and voids. The test involves checking an electric circuit to see if current flows to complete the circuit. This testing is used to find coating film discontinuities that are not readily visible.
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.
Holiday testing is also known as continuity testing.
Holiday testing is a non-destructive test carried out on a coating, such as a rubberized waterproofing coating on concrete, where holes through the coating are detected by the formation of an electrical circuit in areas where there is an insufficient coating to resist the electrical charge. If an electrical flow is detected, then the test area is termed as conductive, indicating the presence of discontinuities such as pinholes and voids. This test is commonly used in the offshore industries where piping and structures are coated with non-conductive coatings.
A holiday test is performed with a holiday detector, which is an electrical device used to determine the location of a gap or void in the coating. There are various techniques and tools available for holiday detection. Coatings applied to concrete substrates can also be tested for discontinuities using either a low-voltage or a high-voltage holiday detector, depending on the coating thickness.
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.