Assessing coating integrity and cathodic protection on buried pipelines under horizontal directional drilling conditions

A moving electrochemical probe technique is developed for probing coating damages on underground pipelines installed by horizontal directional drilling (HDD) and for assessing the efficiency of cathodic protection (CP) through measuring local polarisation currents and local electrochemical impedance spectroscopy (EIS). The capability and accuracy of the probe in detecting coating defects have been evaluated, and compared with current techniques, using a simulated HDD pipe in a borehole. Results show that the probe is able to detect the locations of coating defects over the HDD pipe and that the capacitance of coating defects calculated from EIS data is a rather accurate parameter for defect size determination. The probe has also been used to apply local CP over coating defects for enhancing local corrosion protection. Preliminary field testing on a section of simulated HDD pipe has also shown reasonable accuracy of the probe in determining coating defect locations and sizes.