Holiday testing is a non-destructive test method applied on protective coatings to detect unacceptable discontinuities such as pinholes and voids. 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. This test is commonly used in the offshore industries where piping and structures are coated with non-conductive coatings.
Pinholes and holidays are of much greater concern when coating or lining performance cannot be easily observed, such as a buried pipe or the interior of a tank or vessel. These voids and misses can be detected by performing holiday detection, then repaired before the coating system is put into service.