Failure Analysis Of X80 Pipeline With Corrosion Defects

With the rapid increase of natural gas demand as well as persistent development of natural gas pipeline construction,petroleum industry now prefers pipes of high grade steel and with large diagram to promote transportation efficiency.Since the start of 21 century,as the new generation of high strength and high toughness pipeline steel,the X80 has been widely applied in natural gas transportation industry.However,NG resources are often distributed in remote areas which force the pipeline to go through district with harsh external environment.As a result,the operation of pipeline is often under great danger.Among all the potential dangers,corrosion and according wall thinning is one of the most significant reasons that leads to pipeline failure.In order to avoid such accidents,it is of great importance to study the failure mechanism of corroded X80 grade pipe in depth.That's how we can precisely predict the failure pressure of X80 pipe and make the proper decision on the corroded pipe.Therefore,it is necessary both theoretically and practically to explore the failure behavior and failure pressure.In this paper,the finite element method is an important research method.Refering to available burst experiment data and utilizing Solidworks software,the 3D model of corroded X80 pipeline is build.Then based on ANSYS Workbench software,meshing operation is done of which the steps including optimaizing meshing methods,analysis of grid layer and verification of grid quality.After comparing the results,the failure criteria and reference fauilure presure for X80 pipeline is determined.On the basis of enormous FEM case calculations,the data base of X80 pipe with single corrosion is established.According to the results,study on the failure mechanism of corroded pipe is conducted which includes failure mode,failure process and stress analysis.Besides,factors that affect the failure behavior of corroded X80 pipeline is complished,like depth,length,width,location of defect and the ratio between pipe diameter and wall thickness.At last,the expression of failure pressure of X80 pipe with single corrosion is proposed based on FEM data.The research on the failure mechanism of pipeline with longitudinally and circumferentially aligned double corrosions is complished including failure mode and stress analysis.Furthermore,analysis is conducted to evaluate the influence of longitudinal and circumferential space on the pipeline fauilure pressure.And based on FEM data,the interaction rules of double corrosions on X80 pipe and failure pressure formulars of pipeline with longitudinally and circumferentially aligned double corrosions are proposed.What's more,combining interaction rule with expression of failure pressure of X80 pipe with single corrosion,the evaluation method for pipe with crossing double corrosion defects is put forward and is further verified through burst data.Based on the research mentioned above,further study focusing on complex shaped corrosion is conducted.The available burst experiment of X80 pipe with complex corrosion defects is reviewed,failure mode of test specimen is analyzed and calculation error of different evaluation criteria is compared.Besides,based on FE,the failure mode and stress distribution are analyzed as well as the influence of parameters,including relative depth,relative length and corrosion pit cross-section ratio,on pipeline failure pressure.