Fluctuation Characteristics of Pipe-to-Soil Potentials and AC Voltages on Buried Pipeline under Multi-Source Interference

To evaluate the interference characteristics and corrosion risk induced by stray current from rail transit systems on adjacent buried steel pipelines, the coupon method was employed to conduct long-term synchronized monitoring of pipe-to-soil potentials and AC voltages along the pipeline in the interference zone. Statistical analysis, continuous wavelet transform (CWT), and fast Fourier transform (FFT) were integrated to systematically investigate the fluctuation ranges, attenuation patterns, and time-frequency domain characteristics. The results show that the pipeline's off potentials remained relatively stable during nighttime hours but exhibited intense fluctuations with alternating positive/negative shifts during daytime, demonstrating clear dynamic DC stray current interference features. Statistical analysis reveals that, at 10 test stations along the pipeline influenced by urban rail transit stray currents, the on potential varied from -10.332 V to +2.549 V (vs. CSE), yielding a total fluctuation amplitude of 12.881 V. The off potential ranged from -1.527 V to -0.573 V (vs. CSE), with a fluctuation amplitude of 0.954 V. The interference intensity decayed exponentially outward from the peak point-i.e., the crossing point-though a slight increase was observed at test point S8. CWT and FFT analyses indicate that the dominant frequencies of DC interference were concentrated in the 2.5-7.5 mHz band, corresponding to interference periods of 133-400 s, which aligned well with the typical headway interval of urban rail transit (120-300 s). The slight variations in dominant frequency among different measurement points might be attributed to the time-varying positions of train operations. Furthermore, under the influence of the adjacent high-speed railway, the AC pipe-to-soil voltage fluctuated between 0.004 V and 6.546 V. Its low-frequency components were primarily distributed in the 0.47-2 mHz, corresponding to periods of 500-2 127 s, consistent with the high-speed train headway interval of 900-1 380 s. The multi-source interference characterization methodology established in this study provides foundational data and technical support for stray current corrosion risk assessment, optimization of monitoring parameters, and identification of interference sources.