Study on the influence of metro stray current Based on measurement of close interval potential
                                       QIAN Yao hong1, FANG Jiang min1, MA De liang1, PENG Ze biao2
(1.School of Mechanical & Automotive Engineering South China University of Technology, Guangzhou 510000, China;2.Guangxi Administration of Work Safety, Nanning 530000, China)

Abstract: Aimming at the problems of cathodic protection potential measurement of buried steel gas pipeline under the influence of metro stray current and the evaluation criteria of stray current flowing into and out of buried steel gas pipeline, the measurement technique of close interval potential was introduced into buried steel gas pipeline, switching off potention test was conducted, the relationship between switching off potential and delay time was established, we found that the switching off potential was real cathodic protection potential of pipeline when measurement unit delayed 100 ms. On the basis of the measurement technology of the close interval potential, the buried steel gas pipeline affected by metro stray current was tested, the switching off potential of buried steel gas pipeline under and without the influence of metro stray current were measured( denoted by VoffD and VoffN, respectively). The experimental results show that: when VoffD is positive than VoffN,here is the stray current flow out; when VoffD is negative than VoffN, here is the stray current flow point.

Key words: subway stray currents; measurement technique of close interval potential; steel gas pipeline; cathodic protection potential; switching off potential