Patterns and causes of interference by stray currents from subways on buried pipelines

The interference section of a buried pipeline was evaluated for subway stray current interference. The long-term pipeline on/off potential at 40 test pile locations along the line was assessed using the coupon method. Additionally, at selected test pile locations, the pipeline-to-earth potential was measured simultaneously with the unidirectional conduction device current and track potential limiting device current on the rail side. The extent and pattern of pipeline interference were analyzed, and the practicality of interference evaluation was compared using the Chinese standard GB50991–2014 and the Australian standard AS2832.1–2015. The results indicate that for pipelines affected by subway direct current stray currents, when the subway stray current source is located at one end of the pipeline under study without crossing the pipeline, the sections at both ends of the pipeline are significantly impacted, serving as areas of stray current inflow and outflow. When the subway stray current source crosses the pipeline, the section near the crossing point is heavily affected, with areas of stray current inflow and outflow. This suggests that the stray current entering the ground through the vehicle's over-voltage protection device (OVPD) is the primary cause of significant interference on the pipeline.