Frequency characteristics analysis of pipe-to-soil potential under metro stray current interference using continuous wavelet transform method

Abstract

This study aims to investigate the impact of stray current interference from metro systems on the pipe-to-soil potentials of metallic pipelines, which is closely associated with stray current corrosion. The pipe-to-soil potentials were assessed using coupon testing, while in-situ measurement was conducted to measure the metro leakage currents. The collected field data from the pipe-to-soil potentials and metro leakage current measurements were subjected to a statistical analysis using Continuous Wavelet Transform (CWT) and linear correlation methods. The analysis revealed consistent dominant frequencies of interference at the same test point for both on-potentials and off-potentials conditions, as well as within different time periods. However, variations in dominant frequencies of interference were observed among test points along different sections of the pipeline. Notably, three primary test points exhibited frequencies of 8.3, 8.9, and 7.8 mHz, corresponding to the main interstation travel intervals of neighboring metro lines. Furthermore, the dominant period ranges of interference of metro stray current interference were found to align with the interstation travel interval ranges of the metro lines. When the OVPD acts, the leakage current of the metro station grounding system near the test point has a significant contribution to the amplitude of pipe-to-soil potential fluctuation. These findings highlight the significant role of interstation travel intervals in the periodicity of metro stray current interference. The identified dominant interference frequency ranges can be utilized to determine interference sources and evaluate the extent of metro stray current corrosion.