Research On The Criterion Of The X80 Pipeline With Circular Corrosion Defect Without Strength Fracture

In the service stage of oil and gas pipeline,corrosion will inevitably occur.Corrosion defects will reduce the safety of pipeline.Therefore,countries actively develop fossil energy and increase the import of oil and gas resources,and also attach great importance to the problem of energy security.In China’s oil and gas pipelines,many pipelines are in the stage of overdue service,and the pipeline corrosion is more serious.Therefore,it is very important to study the scale criterion of the circular corrosion defect pipeline without strength rupture.Through access to a variety of documents,obtain the data of the Lan Chengyu oil product pipeline,Lanzheng Changcheng products oil pipeline,Lancheng natural oil pipeline,Zhonggui natural gas pipeline and Sino-Myanmar natural gas pipeline,choose some main types of pipe for research,and use the finite element analysis method to study the influence of three factors on the failure pressure of pipeline,including the outer diameter of pipeline,the thickness of pipe wall and the radius of circular hole.By using the fitting formula,the criterion value(maximum circular hole radius value)of the pipeline without strength cracking is obtained.The corrosion hole is smaller than the maximum circular hole radius value,and the pipeline does not have strength crack.At this time,the corrosion hole is pitting corrosion,and the corrosion defect pipeline is judged.Theoretical guidance is provided for pitting or local corrosion.In the following six aspects related research work.(1)After studying and analyzing a large amount of literature and data at home and abroad,the research and application results of localized corrosion pipelines,pitting pipelines,and analyzed the shortcomings and defects of existing theories and methods.Obtained related nonlinear finite element models and theoretical basis(2)The ANSYS finite element software was used to analyze the corrosion defects of circular pitting pits,and the finite element model pipeline length and model mesh were analyzed,a three-dimensional nonlinear finite element model of a circular corrosion defect pipeline was established.(3)The numerical simulation of the nonlinear finite element of 13200 sets of corrosion-defective pipelines under different working conditions(in-pipe pressure,pipe outer diameter,pipe wall thickness,and circular hole radius)was carried out by ANSYS finite element software,and 110 groups of different influencing factors were obtained.The failure stress of corrosion-defective pipelines is analyzed,and the influence of different parameters on the failure pressure of corrosion-defective pipelines is obtained.(4)Using the finite element software to model another 125 sets of data,the failure of the pipeline was determined by three stress-based failure criteria,and the curve fitting software 1 stOpt was used to curve the analysis data.The formulas for predicting the maximum circular hole radius of three groups of pipelines with circular corrosion defects are obtained.(5)Selected 27 sets of pipelines with different parameters,compared the failure pressure when Von Mises equivalent stress reaches the flow stress and the failure pressure calculated by B31G,Drawn a relative deviation map.Verified the accuracy of ANSYS finite element software modeling(6)Collecting oil and gas pipeline size data on X80 pipelines at home and abroad,and the prediction formula of the maximum circular hole radius of the three sets of circular corrosion defects pipeline fitted by 1stOpt software,Calculating the radius of the limiting hole radius of the X80 pipe at various sizes at home and abroad.The scale criterion for the failure of the circular corrosion defect pipeline does not find the relevant literature data at home and abroad.The pipeline parameters are obtained in the engineering application,and the maximum circular hole radius value allowed by the strength cracking of the pipeline can be calculated.Judging whether the corrosion hole is a pitting that does not cause the strength of the pipe to break or a local corrosion that causes the strength to break.It provides theoretical guidance for the study of pipeline pitting and local corrosion.In the actual operation of the project,the maximum circular hole radius prediction formula is used to provide theoretical guidance for the maximum opening radius value of the pipe with pressure opening operation.It not only ensures the strength cracking of the pipeline,but also ensures the safety of pipeline transportation and avoids economic loss and environmental pollution caused by blind pipeline opening.