Security Study Of Buried Pipelines With Corrosion Defects In Frozen Area

With the continuous exploitation of China's petroleum and natural gas resources,the pipeline has played a decisive role in the development,production and transportation of oil and gas fields.Therefore,the pipeline is called "lifeline engineering",and the construction of direct buried pipeline is more and more.With the continuous deepening of petroleum exploration and development,the oil fields are gradually entering the middle and late stages.With the continuous increase of oil delivery,the corrosion of pipelines is inevitable.Because the soil environment around long distance oil is very complex and the geographical conditions are different,all kinds of geological environment will be encountered during the laying and operation of pipelines.These geological environments have produced a great threat to the long-term safe transportation of pipelines.Especially when the buried pipeline with corrosion defects crosses the frozen soil layer,the role of frost heave and thaw settlement can not be ignored.When the pipeline is corroded in the permafrost region,the thickness of the pipe wall will be thinner or partially thinned,thus the capacity of the pipeline to be subjected to external force deformation is greatly weakened.If the replacement and maintenance are not timely,the overall damage of the pipeline and the oil leakage will be caused.In recent years,earthquakes occurred in China,such as the Wenchuan earthquake,Yushu earthquake and so on.The earthquake action will also cause great damage to the buried pipeline.It is very important to study the seismic performance of the pipeline in the permafrost area under corrosion.The main research contents and research results of the paper include the following aspects:(1)Firstly,the reasons for corrosion failure of oil and gas pipelines,the classification of corrosion and the existing evaluation criteria of residual strength of pipelines are briefly introduced.By consulting the literature and the research needs of the paper,a three-dimensional temperature field model with corrosion defects was established by using ADINA software.(2)Establish the solid structure model of buried pipeline with corrosion defects under the condition of temperature field distribution,and conduct thermal mechanical coupling calculation.The influence of different parameters such as buried depth of pipeline,length of transition section,length of frost heave section,diameter of pipe,length of defect and defect depth on the mechanical properties of buried pipeline in frozen soil area is analyzed,and the maximum position of pipe force is determined.(3)The effect of complex loads on the buried pipelines with corrosion defects under the combined action of earthquake and frost heaving is analyzed on the basis of frost heave,andthe influence of the depth of corrosion,the length of corrosion and the length of frost heave section on the mechanical properties of the pipeline is analyzed.(4)The maximum stress in the finite element analysis results is compared with the circumferential fracture stress in the standard method ASME B31 G and API975.In order to judge the safety of the pipe under the different defect parameters,it provides a reference for the pipeline to continue to run after corrosion.