Study On The Limit Internal Pressure Of The Pipeline With Wedge Dent

During the construction and operation of oil and gas pipelines,plastic deformation often occurs to form dent under the influence of external loads,or due to mechanical construction,the rock compression to form scratches.It is likely to reduce the ultimate bearing capacity of the pipeline greatly by forming a dent in the pipeline with scratches,which will cause the pipeline to fail in blasting and seriously affect the safe operation of the pipeline.For plain dent,the criterion for judging whether the pipeline fails depends on the dent depth reaches 6% of the outside diameter of the pipe or not.The sharpness of the dent is not considered,and the evaluation is too conservative.Most of the current researches are focused on dent pipeline with large curvatures.There are few studies on the pipe that dent are relatively sharp,the radius of curvature is small,especially the research on the residual strength of pipe with small curvature dent and scratches is lacking theoretical support.In this paper,according to the formation of dent scratch,the limit internal pressure of small curvature dent-scratch composite defect pipeline is studied on the experiment method,analytical method and finite element calculation,which provides theoretical basis and technical reference for the evaluation and maintenance of the dented pipeline.According to the formation of dent-scratch,this paper comprehensively uses experiments,analytical methods and finite element calculations,and based on mutual verification,researches on various aspects of the limit internal pressure of a smallcurvature dent-scratch combined defect pipeline to evaluate the dented pipeline,maintenance provide theoretical basis and technical reference.Instead of the full-scale round tube experiment,a small-scale steel plate tensile experiment with a combined dent-scratch defect is designed to study the finite element failure criterion of dent-scratch pipeline.The indenters are respectively small curvature circular indenter and wedge-shaped indenter.The correctness of the finite element model is verified by comparing the experimental data of the steel plate load-displacement curve with the finite element data.In order to determine the finite element failure criterion of pipeline with dent-scratch combination defect formed by the small curvature circular indenter and the wedge indenter,the tensile load of the steel plate with dent-scratch defect are recorded and compared with tensile load that predicted by the finite element method.An analytical solution for limit internal pressure of the intact pipeline is given based on the classic Mises yield criterion.A finite element model was established to simulate the process of dent forming,rebounding and pressurizing of pipe with dent-scratch defect.The ultimate dent depth and ultimate internal pressure of the pipeline with dent-scratch defect are determined according to the finite element failure criterion.From the factors such as pipe size,pipe performance and defect size,this paper studies the limit internal pressure of pipe with the dent-scratch defect formed by the small curvature circular indenter,and obtains prediction formula of limit internal pressure by data fitting.The shape of the dented pipeline is often not regular.In order to better meet the engineering situation,the circular indenter is replaced with a wedge-shaped indenter.The factors such as different scratch length and depth,dent depth,pipe diameter,wall thicknessis analyzed for the limit internal pressure of pipeline and obtained prediction formula of limit internal pressure by data fitting.