Third-party damage leading to leaks and ruptures in line pipe is a major threat to integrity of buried gas transmission systems. In consideration of this situation, Tokyo Gas has developed techniques to detect third-party damage using AC signal. At Tokyo Gas, transmission pipelines are protected from external corrosion by means of cathodic protection (CP) in combination with protective coatings. When an on-line monitoring system is applied on such a cathodically protected pipeline, a problem of deterioration in detection accuracy is caused due to the AC signal leakage into the earth through ground beds via CP rectifiers. As possible measures to suppress the signal leakage, insertion of coil with appropriate inductance, L, between a pipe and a CP rectifier was studied. This paper reports on the results from evaluation tests of an on-line monitoring system when a coil was inserted between a pipe and a CP rectifier. The influence of coil insertion on CP level was also evaluated. The results from field tests have demonstrated the great effectiveness of coil insertion on the suppression of the AC signal leakage and consequently, remarkable improvement in detection accuracy of the system was confirmed. Pipe-to-soil potential surveys revealed that the CP level was not affected by coil insertion. Further optimization of the system in terms of the compatibility with cathodic protection will provide Tokyo Gas with an achievement of more reliable operation of the gas transport system.
On-line monitoring system for detecting third-party damage on cathodically protected pipelines
Online-Überwachungssystem für die Erkennung von Fremdbeschädigungen auf kathodisch geschützten Pipelines
2000
12 Seiten, 9 Bilder, 1 Tabelle, 5 Quellen
Conference paper
English
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