Measurement methods for assessing insulation condition of underground pipelines

This paper discusses the most frequently applied measurement methods for assessing the quality of external insulation along pipelines and detecting defect locations in the protective coating. The quality of coating along a given pipeline section under investigation is assessed by determining unitary resistance of the coating, which is calculated on the basis of measurement results obtained along a pipeline subjected to cathodic polarization. In order to locate defects in insulation of pipelines, methods consisting in measurements of direct current voltage gradient (DCVG) or alternative current voltage gradient (ACVG) are used, mainly on the ground surface for pipelines subjected to polarization by dc or ac current.