what is ideal porosity for a duct?
High voltage holiday detection. High voltage holiday test is normally used to determine the existences of discontinuities in coating films. The high voltage, or porosity technique, can be used to test coatings up to 25mm (1) thick and is ideal for inspecting pipelines and other protective coatings. Coatings on concrete can also be tested using this method. There are two types of high voltage holiday detectors - Continuous DC and Pulsed DC.