Study of corrosion by alternating currents on buried and cathodically protected pipelines near high-voltage power lines

The Buried pipelines of gas and oil, are already protected from corrosion, first by an insulation coating and second by a cathodic protection (CP). The latter reduces the amount of corrosion in order to avoid eventual damage. But, the presence of alternating-current's interferences due to the high voltage power lines nearby, could cause serious corrosion damage on metallic structures, even in CP conditions. Our laboratory's research aims to explain the basic mechanisms of corrosion (electrical and electrochemical) by the alternating current and how to minimize its impact on pipelines. We started an experimental study by modeling the studied phenomenon. The results show that the induced AC current causes the corrosion of the sample that was protected by the CP. Then we continued our study by a numerical simulation of the process. Which gives an E-off (Reference potential measured close to the iron sample) exceeding the immunity zone, a strong oxidation of iron, significant reduction of oxygen, a high liberation of Hydrogen and a clear sample deformation. Lastly, we set up a monitoring and correction program to bring the E-off, in the presence of AC, in the corrosion immunity zone according to standards, this program was able to minimize the reactions of the electrochemical process and prevents sample deformation.