Numerical Simulation Of Local Buckling Of Submarine Pipeline With Groove-type Defects

At present,the depth of offshore oil exploitation has developed into ultra-deep water of more than 1000m.The main failure mode of the pipeline at this time is buckling failure.According to statistics,more than one-third of the North Sea’s submarine pipelines have experienced buckling failure,and the flexion repair is up to 1.5 million US dollars per kilometer.The reduction of the wall thickness of the pipeline will reduce the carrying capacity of the pipeline,thereby reducing the buckling pressure and seriously threatening the safety of deep-sea pipelines.In general,the thinning of the pipe wall thickness is simplified as a groove defect.In order to accurately assess the bearing capacity of corroded pipelines,it is necessary to study and quantify the influence of the depth,length and width of groove defects on the buckling of the pipeline and determine whether the submarine pipeline can withstand the current water pressure,which can help decision makers to develop reasonable maintenance.The plan has certain guiding significance for improving the safety of pipeline operations on the premise of ensuring the safety of pipeline operations.(1)The current research status of pipe buckling theory at home and abroad has been sorted out.Through studying the buckling theory,it is determined that the buckling type studied in this paper is extreme point buckling.(2)By referring to the relevant literature,during the modeling of the pipeline,the Nanhai-Liwan deep-water project pipeline was referenced,and the simplification of the submarine pipeline,marine environment,and pipeline defects was simplified.The main contents included three-dimensional modeling and the ANSYS arc-length method.The determination,mesh number 123400,discussion of material constitutive relations,determination of load and boundary conditions,and Navo Sakakibara crush pressure test verify the feasibility of the solution.(3)Under the effect of pure external pressure,the change of the buckling pressure under the influence of the defect position,defect length,defect width,defect depth and ellipticity of the pipe.By using the mathematical model of origin software fitting,the slope is calculated,and the influence of the depth,width and length of the defect on the buckling pressure is quantified by the slope,and finally the formula for calculating the crushing pressure is obtained.In addition,the stress-strain cloud diagrams with different defect parameters were compared,the stress distribution of the pipelines during buckling collapse was analyzed,and the pressure displacement cloud diagram was extracted,which verified that the research content in this paper is extreme point buckling.The simulated pipeline increases the flexion stop effect of the integrated buckling device,and the crush resistance of the pipeline increases from 10.4 MPa to 22.56 MPa.(4)Under the influence of bending moment,under the influence of the position of the defect,the length of the defect,the width of the defect,the depth of the defect,and the ellipticity of the pipe,the change of the bending moment is calculated by the slope of the curve,and the length,width and depth of the defect are quantified.The influence of the bending moment of the pipe on the bending moment-curvature graph was analyzed.It was concluded that the bending moment-curvature model proposed by Chen Yanfei was no longer applicable when the defect was deep,and the safety bending moment value of the sea pipe was determined to be 300 kN·m.Site construction staff reference.