Investigation On Buckling And Collapse Mechanisms Of Deep-sea Pipes With Dual Corrosion Defects Under External Pressure

Subsea pipelines are an important part of the exploitation of deep-sea oil and gas resources.In the complex environments of deep sea,due to the electrochemical characteristics of seawater and soil and the corrosiveness of transport mediums,the inner and outer surfaces of deep-sea pipelines are prone to generating various corrosion defects during long-term service,which will inevitably result in thinning of the wall thickness of the pipes,and aggravate the occurrence of the buckling and collapse accident of the pipelines.Thus,it is of great theoretical significance and engineering application value to carry out the investigation into the buckling and collapse mechanisms and the assessment of residual ultimate bearing capacity for deep-sea corrosion defect pipes.At present,scholars at home and abroad have carried out numerous researches on the buckling and collapse mechanisms of a single corrosion defect pipe under external pressure,and they have proposed a number of methods to estimate the buckling and collapse pressure of single corrosion defect pipes.However,the actual distribution of the pipe corrosion damage is random,often in form of dual corrosion defects or corrosion groups composed of multiple corrosion defects.The interaction between adjacent corrosion defects has a significant effect on the collapse mode and collapse pressure of dual corrosion defect pipes.Based on the available literatures,the research on the buckling and collapse mechanisms of deep-sea dual corrosion defect pipes under external pressure has been rarely reported so far.In view of this,in this paper,a combination of small-scale experiments and numerical simulations was applied to study the buckling and collapse mechanisms of deep-sea dual corrosion defect pipes under external pressure.The main work can be summarized as follows:(1)The small-scale model experiments of deep-sea dual corrosion defect pipes under external pressure.The experimental devices of self-developed hyperbaric chamber were used to conduct the buckling and collapse tests of steel tube specimens with axial dual corrosion defects,circumferential dual corrosion defects and diagonal dual corrosion defects under external pressure.The influence mechanisms of defect position orientation and defect spacing on the buckling and collapse of steel tube specimens with dual corrosion defects were investigated,and the collapse pressure,deformation configuration and collapse mode of each steel tube specimen with dual corrosion defects were analyzed,which provided a verification basis for establishing reasonable finite element numerical models.(2)Numerical simulations on the buckling and collapse of deep-sea dual corrosion defect pipes under external pressure.Using the finite element software ABAQUS,the three-dimensional finite element numerical models of steel tube specimens with axial,circumferential and diagonal dual corrosion defects were established,respectively,to simulate the buckling and collapsing process of each steel tube specimen,and the feasibility and accuracy of numerical models were verified by comparing with the experimental results(3)Parametric dependence analysis on the collapse pressure of axial dual corrosion defect pipes and circumferential dual corrosion defect pipes.The numerical models of axial and circumferential dual corrosion defect pipes were developed to perform extensive parametric sensitivity analysis.The influences of pipe and defect geometric dimensions,mechanical properties of steel,defect spacing and defect position orientation on the collapse pressure of pipes with axial and circumferential dual corrosion defects were investigated,respectively,and the effect law of the interaction between adjacent corrosion defects was analyzed.