Fault Diagnosis and Elimination of Cathodic Protection System for Long-distance Buried Pipelines

Due to outside interference, coating damage and other factors, the cathodic protection potentials of pipelines are often less protected, over-protected and unusually fluctuate and so on. By using Fluke digital multi-meter potential measurement, DC voltage gradient measurement (DCVG) and pipeline current mapper (PCM) and other non-excavation of buried pipeline NDE techniques, a comprehensive on-site fault detection and diagnosis was done for the cathodic protection system for a long-distance buried oil pipeline. Besides, the located soil corrosion and the coating of the buried pipeline were tested and assessed. The results showed that the cathodic protection potentials measured from some potential test piles along the pipeline were beyond the cathodic protection potential criterion range (from -850 to -1 200 mV,CSE). Some cathodic protection potentials of the pipeline showed frequent abnormal fluctuations, multiple damage points of coating were detected, and some exhibited positive corrosion activity. The results showed that a section crossing under the concrete used the casing protection, high-speed rail and so on were built later and located nearby the pipeline, there was paralleling or crossing somewhere. The cathodic protection potential shielding, stray current interference and other issues were discussed, and reasonable drainage measures and sacrificial anode were proposed.