Holiday test ：
a. Purpose: To detect pinholes, crack, and damage coatings on conductive substrates, therefore, to provide an effective safeguard against corrosion.
b. Principle:
Using a low frequency high voltage to delivers a stabilized pre-set pure DC outputs via a probe to an inspection electrode. As the electrode moves over the coated surface, a small current flows actuating a visible sparkle at the point of contact, if it encounters a pinhole or flaws.
c. Application:
1) Coated piping
2) Coated tanks and vessels
3) Concrete coating
4) Steel structures coating
