Reaction Analysis Of High Strength Pipeline Steel With Corrosion Defects In Active Faults

With the development of the national economy,the level of industrialization and the improvement of environmental requirements,people's demand and dependence on clean energy such as natural gas has increased year by year.Pipeline is the most important and effective way of oil and gas transportation in China,which is called an important lifeline system.However,the pipeline is mostly buried in the ground,crossing a wide range and a complex geological environment along the line.It is highly vulnerable to various geological disasters such as earthquake faults,landslides,collapses,and ground subsidence.At the same time,it is difficult to avoid corrosion problems during pipeline operation,resulting in pipeline failure and destruction.The stable and continuous supply of natural gas energy has become an important guarantee for the industrial,agricultural and residents' stable production and life.Therefore,ensuring the safety and reliability of oil and gas pipelines plays a vital role in the energy transmission of the pipeline network.In this thesis,we use the method of Non-linear Numerical Simulation to study the influence of different defect parameters,pipeline operation parameters and fault parameters of X70 pipeline with corrosion defects under active faults,in order to provide theoretical support for the safe operation evaluation of pipelines with corrosion defects under faults.The main research contents are as follows:Firstly,Investigated and analyzed the main research methods and progress of buried pipelines across faults,and the applicability of the current safety evaluation criteria for pipelines with defects in high strength steel.Then the finite element software was used to establish a three-dimensional corroded pipe soil interaction model through the strike-slip fault.The pipeline and soil used C3D8 R solid elements,and the Mohr-Coulomb model and the Ramberg-Osgood model were used to describe the stress and strain bombs of the soil and pipeline.Plasticity;In the contact pair algorithm,the face-to-face discrete method is adopted,the normal action of pipe-soil interface is described by the hard contact model and the tangential action is described by the penalty function model,and the calculation area of 50m*10m*10m is determined by the model scale trial calculation,and the uniform wall thickness defect is used as the defect shape of the pipe material.We used the model of pipe soil to analyze 10 sensitivities such as defect hoop orientation,defect axial position,defect depth,defect length,defect width,pipe internal pressure,pipe depth,fault dislocation,fault dip angle and fault type.factor,to study the variation trend of stress and strain in the defect area and the peak value of original mechanics of buried pipeline under different parameters,and to explore the mechanical characteristics of pipeline under this condition.The circumferential failure stresses of ASME B31 G,API579,PCORRC and DNV-RP-F101 are calculated to analyze and evaluate the stresses at pipeline defects under different working conditions.It is suggested that appropriate evaluation methods should be selected for safety analysis of pipelines with corrosion defects under fault dislocation to evaluate their applicability.The stress assessment of corrosion defect by stress-based method alone can't completely determine whether the pipeline is safe or not.It is also necessary to use strain-based evaluation criteria to evaluate the maximum strain of pipeline in the fault-affected area to ensure the safe operation of pipeline.