| Under the same external conditions,the PSP(pipe-soil potential)fluctuation of the pipeline near the abnormal point of the earth’s transverse conductivity is more intense,which is easy to aggravate the pipeline corrosion,greatly shorten the expected service life of the pipeline,Therefore,it is very necessary to study the influence of the earth transverse conductivity anomaly on PSP.The main work and conclusions of this paper are as follows:(1)Vortex current is a special phenomenon of surface current caused by static earth conductivity anomaly,which will have certain influence on PSP.Taking southwest China as an example,based on Fourier,finite element and other algorithms,this paper discusses and analyzes the influence of air current source on complex earth GIC(Geo Magnetic Induced Current),and gives the formation mechanism of vortex current and its influence on pipeline PSP.The results show that the vortex current is due to the asynchronous change of surface current in different conductivity plots under the same current source,and even the phenomenon of "current reversal" in a certain period of time.When the pipeline passes vortex current,the positive and negative of the electric field in the pipeline on both sides of the vortex center may be opposite.PSP will turn at the positive and negative change of the electric field in the pipeline,which may cause PSP on both ends of the pipeline to behave in the same direction,and GIC will realize zero crossing in the middle of the pipeline.In this paper,the accuracy of the relevant conclusions in this paper is verified by the actual calculation results of the southwest surface current and PSP of China-Guizhou pipeline from 12:00 to 20:00(Beijing time)on March 17,2015.(2)Seawater tide will cause abnormal dynamic changes in the conductivity of sea and land and make PSP in coastal areas have obvious double peaks and double valleys diurnal variation characteristics.In this paper,the mechanism of tidal action on the pipeline PSP and the calculation method of "time division and space division" of the pipeline PSP considering tidal action are put forward,and the accuracy of the mechanism is proved by taking the pipeline in the eastern section of the third line of west-east gas pipeline as an example.The results show that the essence of tidal pipeline is the dynamic movement of seepage interface in time domain and the polarization effect of interface.The closer the pipeline PSP is to the coastline,the more seriously it is affected by the tide.When the seawater reaches its maximum,the most serious impact is on the pipeline PSP.(3)The pipeline near the abnormal point of the earth’s transverse conductivity is more seriously affected by geomagnetic field and is the key protection object in the whole pipeline network system.In this paper,the Parkinson vector of the improved algorithm is proposed,and based on the unique properties of the vector at the earth’s transverse conductivity interface(the azimuth angle changes from±180° to 0° or 0° to±180° at the interface and the length reaches the minimum value at the interface),a set of methods for finding the earth’s transverse conductivity interface under the pipeline are proposed,and three stations of Longyan,Zhangzhou and Quanzhou in the eastern section of the third west-east gas transmission line are taken as examples for analysis,and the accuracy of the method is verified.These conclusions have important guiding significance for pipeline protection in China. |
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