Discontinuity (Holiday) Testing of New Protective Coatings on Conductive Substrates
|Publication Date:||1 March 1999|
This standard provides procedures for low-voltage wet sponge testing and high-voltage spark testing of new coatings on conductive substrates.
Electrical testing to determine the presence and number of discontinuities in a coating is performed on a nonconductive coating applied to a conductive substrate. The allowable number of discontinuities should be determined prior to conducting this test, because the acceptable number of discontinuities varies depending on coating thickness, design, and service conditions.
This standard is not intended to provide data on service life, adhesion, or film thickness of an applied coating system. Electrical testing does not detect areas where the coating is thin (even as thin as 25 μm [1.0 mil]).
This standard is intended for use only with new coatings applied to conductive substrates. Inspecting a coating previously exposed to an immersion condition could result in damage to the coating or could produce an erroneous detection of discontinuities due to permeation or moisture absorption of the coating. Deposits may also be present on the surface, causing telegraphing. The use of a high-voltage spark tester on previously exposed coatings can result in a spark that damages an otherwise sound coating. A low-voltage wet sponge tester may be used without damaging the coating but can produce erroneous readings.
To prevent damage to a coating if a high-voltage spark tester is being used, the total film thickness and dielectric strength of the coating system shall be considered in selecting the appropriate voltage for detection of discontinuities.
The coating manufacturer shall be consulted to obtain the following information, which can affect the accuracy of the tests described in this standard to determine discontinuities:
(a) The length of time required to adequately dry or cure the applied coating prior to testing. Solvents retained in an uncured coating may form an electrically conductive path through the film to the substrate.
(b) Whether the coating contains electrically conductive fillers or pigments that may affect the normal dielectric properties.