Stray Current Corrosion and Mitigation: A synopsis of the technical methods used in dc transit systems

Abstract

© 2013 IEEE. As a result of the dynamic nature of the stray-current problem, it is challenging to control the stray current within allowable limits. However, with appropriate design decisions, meticulousness during construction, and a proper maintenance and testing regime, the stray-current leakage can be controlled within limits. The recent advances in the stray-current collection have also validated the use of a combination of mitigation methods and collection techniques for the control of stray current. The common application of this approach includes the use of rail boot and other design and construction mitigation techniques such as insulated fasteners, substation spacing in combination with steel reinforcement mesh, and a currentcollection technique. It can be concluded that although the technical advancements have been made in the mitigation and collection techniques for stray currents and new methods have been implemented by transit agencies, most of the mitigation methods used today are the same as suggested by the corrosion committees in the early 1920s. In transit agencies that have a regular maintenance and testing plan along with correctly designed mitigation measures, it was observed that they have a better handle on the stray-current leakage. This makes the regular testing of the tracks an important aspect, and this cost should be accounted in the transit agencies maintenance budget. In fact, assessment of the potential corrosion resulting from stray current should be a part of the planning and design process at the very inception of all projects and the testing of the stray-current corrosion must continue through the revenue service. Another aspect that was realized during the research is the need and importance of having trained corrosion-control staff on the transit agency payroll. Transit agencies are aware that stray current is a serious issue, and it would benefit them greatly if their staff is trained on the fundamentals of the stray current. This would not only help address any potential stray-current issues early on but would also aid the transit agency in conducting early testing of the rail track. Additionally, it was observed that the transit agencies are not keeping a log of the corrosion issues caused by the stray current and the money spent to mitigate those corrosion problems. This kind of tracking would be extremely beneficial to the rail industry in assessing the economic and logistic burden borne by rail transit agencies as a direct impact of stray-current corrosion. Stray-current issues have been around since the first electric railways were placed into operation and can create safety hazards and have serious effects on utility structures and the transit infrastructure itself. Since most of the heavily affected systems are street railways or trolleys, the areas in which the railways were built were also most likely to have underground metallic structures like utility piping, thus making it necessary to have stray-current leakage control. Although more of an issue in embedded tracks and tracks with low soil resistivity, stray-current corrosion is a concern for all kinds of track and needs to be addressed during the design, construction, and maintenance of dc-powered rail transit systems.