A method for in-situ detection of coating defects on a buried pipeline. The pipeline is under cathodic protection or otherwise carries a current applied to its pipe walls. A magnetic field sensor array is placed within the pipeline and moved along its length. As the sensor array travels, it detects the magnetic fields within the pipeline. The sensor output is compared with “expected” data, which represents interior magnetic fields of the pipeline without coating defects. Because electrical current leaks through a coating defect, the current is altered on the pipe wall at the defect. This in turn alters the interior magnetic fields, and a change in the interior magnetic fields indicates a coating defect.