Stray current is defined as the existence of electrical potential that can be found between objects which should not be subjected to voltage.
One of ICG’s projects involve working to prevent stray current corrosion caused by light rail transit systems. In 2010 a local gas utility company noticed during daily operations the light rail system was leaking stray current from the rails into the ground. This is problematic as current discharged into the ground flows along paths of lesser resistance. These paths of lesser resistance can be highly conductive (low resistivity) soils, or metallic conductors (such as pipelines and other metallic utilities). Should the stray current hop onto one of these utility pipelines acting as a conductor, it can continue traveling and eventually discharge from the conductor to the traction power substation (see figure below). Leading to metal loss and potentially pipe failure.
Once a stray current occurrence was identified the local gas utility and the light rail operator quickly formed a cooperative with the goal of creating a Long-term Data Logging Program. The programs’ goal is to identify and mitigate these stray currents. Ultimately, reducing corrosion on any pipelines within the vicinity of the rail lines.
Who better to bring in on a long-term corrosion control effort than Infinity Corrosion Group? In April, 2015 ICG joined this effort and since then has been monitoring dozens of at-risk utility sites due to their proximity to the light rail system. The sites are monitored by data loggers which continuously record pipe-to-soil potentials. By bringing this continuous data stream into Grapher, Zach can document patterns and changes in key variables that provide insight to the need and type of mitigation or remediation required at these sites along the light rail system.
One way Zach uses Grapher to document these changes is by plotting the pipe-to-soil potentials for each utilities test point. These plots are called Stray Current Plots and are used to simultaneously keep a historical record and monitor new stray current events. Grapher’s customization options provide Zach with the ability to utilize multiple axes and color schemes; ensuring his team can take one look at the plot and quickly determine when a new stray current event has occurred.
The below Stray Current Plot represents data collected in November of 2018. The Y-axis on the left denotes the pipe-to-soil potential voltage readings, and the X-axis represents the time in days. The four different background colors of blue, green, yellow, and red represent the different stray current corrosion risks. The two Y-axes on the right side of the plot correspond to the temperature and precipitation denoted by the darker blue line and light blue bars respectively.