Investigation And Control Analysis Of Stray Current In Jiao Ri Natural Gas Pipeline

There are many alternating current(AC)and direct current(DC)transmission lines,electrified railway,electric equipment,various types of underground pipeline in Qingdao which is a highly developed economic zone.In city planning,however,these facilities use the same route due to the limitations,leading to the complex distribution of the lines,many crossing points and long parallel line.Therefore,the stray current interference on buried pipelines caused by the power facilities is inevitable,and the parallel pipeline will affect each other.The analysis and examination of stray current is of great importance to the safe operation of pipelines.According to the principle of electrochemical corrosion,the interference mechanisms of DC stray current and AC stray current are expounded in this paper.The soil corrosivity was analyzed by the measured soil resistivity along the pipeline.The pipe-to-soil potential is acquired by the data recorder with the polarization of the probe so that the IR is relative small.Then the plots of the whole pipeline potential and AC corrosion density are drawn.According to the pipe-to-soil potential and the AC corrosion density,it is found that the gas pipeline is under the effect of DC and AC stray current interference.For the DC stray current interference,according to the comparison of the natural potential of different test pile at the same time,the pipeline stray current flow direction is determined.Combined with the potential gradient,the DC stray current interference source is located,and the influences of the parallel pipeline,large industrial power supply station and the tides on the stray current interference of the pipeline are analyzed.It is found the large industrial power supply station and the tide are the DC stray current interference sources.For the AC stray current,the AC voltage and AC potential density are adopted as evaluation criterion,and the AC interference sources are investigated.It is found that the AC high-voltage transmission lines is the actual AC stray current interference source.The different voltage of transmission lines and relative position will lead to different potential.The combination of the discharge bed and the solid state decoupler is adopted in this gas pipeline.The results show that the method effectively reduces the pipeline potential and the loss of the cathodic protection current.But it is better to check the performance of solid state decoupler.The failure of the solid state decoupler will cause the stray current flow from the bed,leading to the pipeline potential abnormal and the fault of the cathodic protection system.Finally,in this paper the advantages and disadvantages of the constant potential mode and the constant current mode are analyzed in the operation of the cathodic protection system.