Seismic Security Study Of Oil Pipeline Containing Crack Defects

With the rapid development of petroleum industry, the pressure pipelines have been moving into the period of high incidence of accidents, the crack defects of oil and gas pipeline has become one of the biggest hidden dangers of the pipeline’s safe operation. At the same time, China is an earthquake-prone country, earthquakes occurred frequently in recent years, which not only brought great loss to people’s life and property, but also caused serious losses to the oil transportation system. So it has become an urgent problem to investigate the seismic performance of pipeline containing crack defects.In the first chapter, the research background and research significance of buried pipelines were described under the action of earthquake load, and some typical examples of earthquake damage of pipelines were brief listed. The principle of cracking and fracture patterns of pipeline was simple described, the research methods of thesis and the theoretical analysis model of pipe-soil interaction were proposed.In the second chapter, the theoretical seismic analysis method of pipeline structure and the time-history method of numerical analysis were introduced, the numerical analysis model of oil pipeline containing crack defects was established with ANSYS. Due to the impact of the fracture stress field and displacement field, the SOLID95unit was used to characterize the singularity of crack tip in the finite element model, and the SOLID45unit was used to divide non-crack area of the pipeline, the COMBIN39unit was used to simulate soil spring under the action of inner pressure. The influences of crack defects on the seismic performance of pipeline were studied through the numerical results analysis of time history curves of acceleration, displacement and stress of crack tip points of pipeline containing crack defect and pipeline with no defect.In the third chapter, the influences of size fracture parameters on the seismic performance of pipeline were studied in the same soil conditions, including the depth of the crack, length of the crack and wall thickness, and the influence of different parameters on the pipeline seismic were discussed through the time-history curves of each particular node and the analysis of their stress-strain values.The finite element analysis models of oil pipeline containing crack defects were established under different site conditions, the impact of site conditions on the seamed pipes’seismic performance was also investigated.In the fourth chapter, the applicability of oil pipeline containing crack defects was discussed with R6criteria and API579criteria, the maximum calculated stress value and the theoretical value of circumferential fracture stress were compared, which was used to judge the security of the pipeline’s different effects when earthquake occurred, then the theoretical basis was provided to judge whether the oil pipeline containing crack defects can service.