1.1 Electrical inspection (holiday detection) is a test of the continuity of a protective coating. This type of inspection does not provide information concerning coating resistance, bond, physical  characteristics, or the overall quality of the coating, nor is it intended to do so. It will detect bubble or blister type voids, cracks, thin spots, and foreign inclusions or contaminants in the coating that are of such size, number, or conductivity as to significantly lower the electrical resistance or dielectric strength of the coating.

1.2 Electrical holiday detector: A device for locating discontinuities in the coating.

1.3 Use of a holiday detector should be at the discretion of the coating inspector. An initial holiday inspection, performed as soon after the application of the coating as practicable, serves to check the materials and the application procedures. A final coating inspection, before the coated pipe is placed in the ditch, will disclose any defect or damage to the coating, except disbanding, which has occurred during the construction period. 

1.4 This recommended practice presents acknowledged techniques in the use of holiday detector equipment currently used on pipeline coatings prior to lowering-in operations and presents a table of recommended voltages for various coating thicknesses.

Historical Document 1998