ABSTRACT

A study of alternating current (AC) interference on cathodically protected pipeline from railway electrification systems was conducted. A continuous data logger capable of measuring the pipe to soil potential at a sampling interval of 1.25s was developed specifically for the purpose. The study was carried out in a 51mm diameter underground pipeline running parallel to the rail line for a distance of nearly 150m. The data logger was placed securely inside a test link post (TLP) with its positive terminal connected to the pipe and the negative terminal to the copper sulfate reference electrode (CSE) buried underground. A maximum of 33 Vrms and a minimum of 5 Vrms were found to be induced in the pipeline when the rail was energized. These measures help us to assess the risk of corrosion and mitigation measures to be implemented, thereby contributing to sustainable corrosion prevention. The present paper presents the scheme of the experimental system, important aspects of the instrumentation part and the major results, along with the author’s plan for future studies.

INTRODUCTION

Interference from AC powered rail lines can contribute an electric shock hazard and even a threat to the pipeline metal during both fault and load conditions. A metallic pipeline which is buried in the vicinity of AC powered rail lines becomes energized by the electric and magnetic field originating from the rail lines. In addition to this AC current can enter the pipeline when electric charges are injected into the soil under steady state and fault conditions of the rail lines. The AC interference on pipelines can cause electric shock hazard to people touching the pipeline or metallic structures connected to the pipeline or simply standing nearby. Mitigation systems are designed to reduce the interference voltages to a safe level during both load and fault conditions of the rail lines. Shielding, grounding, use of gradient control mats and polarization cells are some of the proven mitigation techniques. Among these the use of solid state polarization cells is found to be more efficient and is gaining popularity now a day. The conceptual design of a low cost solid state polarization cell is also included as a part of the study.

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