Combined effect of coast and fault zone on pipeline in Eastern China

The geomagnetic induced current (GIC) and earth surface potential (ESP) in conductive earth induced by the low-frequency geomagnetic disturbances directly influence pipe-soil potential (PSP) on buried pipelines which may contribute to the pipeline corrosion. It can be difficult to study the coastal telluric field and its influence to pipeline at large temporal and spatial scale because of complexity of earth conductor and geo-electric field. Firstly, we constructed a three-dimensional thin shell model to explore the relationship between electric field distribution and fault zone conductivity in coastal areas. We found that the electric field in the coast-fault zone was increased when the resistance in the fault zone was smaller than that in the coast fault zone. Then,with the earth conductivity data in coastal areas of Eastern China, we constructed the three-dimensional earth conductivity model where Ri-dong pipeline of China National Petroleum Corporation’s (CNPC) went through. Based on the Finite element method (FEM) coupled with the Fourier transform, the theoretical model for PSP during magnetic perturbation was established in this paper. Taking the magnetic disturbance between October 12, 2016 and October 14, 2016 as an example, we calculated numerical PSP by PFFEM applying the magnetic data from geomagnetic observatory as boundary condition. Finally, the calculated and measured value of PSP in Rizhao and Yanzhou stations along Petro China Ri-dong line were compared, which proved the validity and feasibility of the model and the algorithm. From the spatial distribution, we could analyze the relationship between the important nodes of pipeline PSP and the changes of pipeline model parameters. The temporal distribution showed that the numerical value and fluctuating amplitude of PSP in coast-fault zone is larger, which further verifies the influence of the fault zone effect on the pipeline. Analysis results of both the model and the measured data revealed the distribution of PSP in coastal pipelines under the combined effect of coastal and fault zones, and provide a prediction way for subsequent pipeline maintenance.