Research on Stray Current Corrosion Evaluation of Buried Metallic Pipeline in an Urban Rail Transit System

In this paper, a research is made on the stray current corrosion evaluation of buried metallic pipeline in an urban rail transit system. The long-term accuracy of the polarization potential measurement is found not to be perfect for the stray current corrosion evaluation, which is caused by the life cycle, the working condition and the IR drop error of the reference electrode. Furthermore, according to the Faraday's laws of electrolysis, an optical fiber sensing method is proposed to measure the stray current, which can be applied to evaluate the stray current corrosion status directly. The maximum of the stray current is found to be 20 A. And the design principle and configuration of the optical fiber sensing system are demonstrated. Moreover, the comparison is conducted between the polarization potential measurement results in 2004 and the results in 2010, which verifies the analysis results on the imperfect long-term accuracy. In addition, the transient response test and accuracy test of the optical fiber sensing system are conducted, which indicates that its response time and relative error are less than 0.73 ms and 0.4%, respectively. Finally, the stray current corrosion status of the pipeline phi 76 x 10 are evaluated based on the results of the direct measurement method, which indicates that the corrosion perforation will be caused in anode region if the corrosion time is greater than 2 months and 11 months at 20 A and 4 A, respectively.