Wet Sponge Holiday Detector
Definition - What does Wet Sponge Holiday Detector mean?
A wet sponge holiday detector is a device that uses a wet sponge to perform a holiday spark test for the purpose of detecting discontinuities, or holidays, in a non-conductive coating over a conductive material. A wet sponge holiday detector uses a low voltage that traverses through the sponge’s fluid and causes a current to form where holidays are present. Detection of holidays is coupled to an audible alarm and/or light to inform the tester of the discontinuity.
Being a low voltage holiday test, the device is applicable for coatings up to 500 microns in thickness and uses a non-destructive technique to prevent damaging the coating.
Corrosionpedia explains Wet Sponge Holiday Detector
Normally, holiday spark tests fail in the presence of moisture. However, wet sponge holiday detectors take advantage of water or another conductive liquid to enhance the holiday test. The liquid seeps into the small pores of discontinuities. To make the system work the detector's ground cable is typically connected to the conductive substrate. This connection allows the electrical circuit to complete through the coating in the presence of a holiday. Alternatively, the conductive substrate itself can be grounded.
Wet sponge holiday detectors use different sponge shapes for different applications because the shape affects the contact surface area. Both flat and roller sponge types of detectors are available. Roller sponges can increase the speed of the testing process. Cellulose sponges are used instead of rubber or urethane sponges (which do not work).
Cleanliness of the sponge and surface is important because contamination can add resistance to the current flow.