With the large-scale construction of metro systems in many cities of China a growing number of buried metal pipelines are suffering from dynamic DC stray current in recent years. However less work has been carried out on the effect of dynamic DC stray current on corrosion rate of steel structure therefore there is a lack of consistent corrosion evaluation criterion under dynamic DC stray current in the world currently. Based on measured dynamic fluctuating parameters on buried pipelines interfered by dynamic DC stray current from metro system the fluctuation characteristics such as fluctuating period waveform and amplitude were analyzed systemically. Corrosion coupons were buried near the pipelines interfered by dynamic DC stray current and connected electrically with the pipeline and after 6 or 12 months the corrosion coupons were dig out and corrosion rates of them were obtained by weight loss tests. The relationships between dynamic fluctuation parameters and corrosion rates were analyzed which could provide reference for the buildup of corrosion evaluation criterion under dynamic DC stray current.
Stray current is a major concern for the track utility and infrastructure owners in the vicinity of thedirect current (dc) powered rail transit system.Stray current leakage and the corrosion caused by these currents is more of an issue in low resistivity soils and embedded tracks which typically run through major traffic areas city centers and tread between utility lines that require the rail to be continuously isolated to provide superior track-to-earth resistance.The absence of specific national stray current control and/or mitigation standard or guideline in the U.S necessitates the need to produce contemporary standards and guiding principles for the transit providers and corrosion consultants to match the advancements made in other sectors of the rail transit system. The author thus prepared a guidebook for the Transit Cooperative Research Program (TCRP) documenting best practices for those seeking guidance on design maintenance and testing of stray current control for dc powered rail transit systems. The guidebook is a resource that can be put into use immediately by stray current corrosion consultants transit agency owners and corrosion testing and maintenance providers.This guidebook includes the study of both national and international transit agencies. It is formatted as a reference guide to provide a user-friendly framework of consolidated guidelines and recommendations that will help in mitigating and/or eliminating stray current leakage from dc operated rail tracks using the data collected from transit agency and corrosion consultant interviews stray current corrosion survey questionnaires and field testing of a mix of 30 transit agencies (21 national and 9 international).This paper discusses “Lessons Learned” on the problems of surveying the transit industry how they were overcome and the results of a case study on issues related to stray current effects from one of the transit agencies that were used in preparing these consolidated guidelines and recommendations.