Holiday Detection of OAP Coatings
The visible range of the electromagnetic radiation spectrum is typically between 400nm and 760nm. UV-A range, which is used for OAP inspection, falls between 320nm and 400nm. Presently in development are holiday detectors that can contain either the lamp or LED light required to illuminate the film, and a camera sensor to scan the coated surface. The lamp/sensor head is typically connected to a small analyzer pack, which holds the controls and electronics to operate the holiday detector. This set-up is not unlike current holiday detection equipment, which uses either a high voltage wire brush or low voltage sponge wand connected to a power device/audible alarm. When the OAP analyzer detects a holiday in the coating film, it beeps to alert the inspector. UV blocking glasses are worn when using UV-A lamps. Some LED light manufacturers include a classification statement designating many of their products as Class 1 LED. Class 1 LED devices are defined as requiring no eye protection.
Using these instruments, the tester can cover approximately 150 square feet per minute, a rate almost as fast as the tester can move his hand in a sweeping motion. Furthermore, since the instrument does not have to be grounded or in direct contact with the coated surface, sweeps of large areas or areas that typically would be difficult or impossible to inspect with a conventional holiday detector can be done efficiently and quickly.
Visual Inspection of Fluorescing Coatings
A much greater benefit to the use of OAP coating technology comes from what can be done beyond simple holiday detection. Coatings manufactured with OAA can be made to fluoresce simply by illuminating the appropriate lamp or LED. Visual inspection under the appropriate lamps will show the fluorescing coating’s presence in a coating system. When a fluorescing coating is used as the epoxy prime coat of a two-coat interior coating system (such as the AWWA D102-03 Interior Coating System No. 1), simple illumination of the primer before topcoating will reveal holidays, pinholes and areas of insufficient film thickness. Although the use of holiday detection instruments would alert the inspector to pinholes not visible to the naked eye, black or dark spots would visually indicate holidays and pinholes when the OAP coating is illuminated.