Failure Mechanics Analysis Of High Steel Grade Pipes With Corrosion Defects

In today’s situation,the most ideal form of oil and gas resources transmission is steel pipeline.Due to the complex and diverse environment of soil and temperature,corrosion of steel pipelines is inevitable,resulting in lower failure pressure and,in serious cases,perforation,leakage and cracking of the pipeline,causing environmental pollution and economic losses,so the study of failure pressure and residual strength of pipelines with corrosion defects is of great practical importance.However,most of the current research is limited to single or double corrosion defects,and few scholars at home and abroad have carried out in-depth research on the failure mechanism of more numerous and more complex group corrosion defects,especially in X80 high steel grade pipelines.Therefore,this paper uses ABAQUS simulation software,for single corrosion,double corrosion,group corrosion defects X80 steel pipe,the failure analysis and the remaining strength prediction of the pipe,the main research content and research results are as follows.(1)On the basis of research into the failure analysis of high-strength steel pipes containing corrosion defects and the current situation of the evaluation of the remaining strength of pipes at home and abroad,the technical route of this paper was formulated;a non-linear finite element model for single corrosion,double corrosion and group corrosion defect pipes was established,and the reasonable accuracy of the model was verified by combining real burst test data and the error comparison with various existing evaluation standards.(2)On the basis of a model of a high-strength steel pipeline containing corrosion defects,the effects of different defect depths,lengths,widths,axial spacing and internal pipeline pressures on pipeline stresses were investigated.Sensitivity analyses were carried out for each factor and the following main conclusions were obtained:(1)the sensitivity of each influencing factor of single corrosion defect high strength steel pipe failure from strong to weak order: defect depth,defect length,defect width.(2)The failure pressure decreases as the depth or length of the double corrosion defect increases,and increases as the axial spacing increases and its growth rate decreases;the size of the interaction is affected by both the depth of the double corrosion and the axial spacing between the defects.(3)the most critical factor in determining the damage form and failure pressure of the group corrosion defect pipe is the depth of the deepest defects in the corrosion group.The size of the corrosion defect depth is the impact of group corrosion pipe failure and the location of the maximum equivalent force of the pipe is the main factor,and the length of class II defects and the axial spacing between the corrosion group is a secondary factor affecting the failure pressure of the pipe.Notably,group corrosion defects with reduced wall thicknesses will markedly reduce the failure pressure of the pipeline.This must be considered in actual projects.(3)Based on DNV criterion,the modified DNV formula with modified coefficientβ was introduced to establish the residual strength prediction model of pipelines with group corrosion defects.The research results can provide a reference for failure study and residual strength evaluation of high-grade pipelines with group corrosion defects.