This document specifies procedures for detecting the presence of porosity in a protective paint system of any thickness on a steel or other metallic substrate. The procedures given in this document are based on methods using two different types of test equipment, the choice of equipment depending on the dry film thickness. These procedures are only applicable to the testing of electrically non conductive parts of a paint system. The test methods specified are mainly intended for use with new coatings, but can also be used for coatings which have been in service for some time. In the latter case, it is important to bear in mind that the coating might have been penetrated by substances in contact with the coating during service.