On The Buckling Instability Mechanism Of Deep-sea Pipeline

At present,offshore oil and gas industrry has gradually marched into the field of over 500 meters deep water and ultra deep water,and the wall thickness design of submarine oil and gas transmission pipeline presents an increasing trend.Local buckling collapse and buckling propagation are the most important structural failure modes under the condition of high water pressure,which directly determines the engineering design of the main parameters of the structure.For the collapse problem of thick-walled pipeline,industrial circles believe that the current recommended methods in DNV-os-F101 specification,which is considered to be more general and authoritative,might be not precise enough and leading to too conservative estimation,thus reducing the economical efficiency of the project.Therefore,the buckling effect of submarine thick-walled pipeline was studied in this dissertation from the theoretical method of calculating the standard value of collapse pressure,the values of empirical coefficients and the influence of complex loading,in order to provide reference for deep-water oil and gas developing projects in South China Sea.Take the thick-walled cylindrical shell of the pipeline pipe and the integral buckling arrestor as the research object: First,based on the high order shear deformation theory of moderate thick shell,the method for calculating the collapse pressure of thick-walled pipeline was established and programmed,with the reliability verification by the comparation between the theoretical results with the experimental results and the 3D finite element simulation results in ABAQUS.Furthermore,the sensitivity analysis was carried out,and the conservation the DNV calculation method of standard value under small diameter-thickness ratio was discussed;Second,the ring-truss theoretical model was established to analyze the mechanical essence of pipeline buckling propagation,and quasi-static experiments of propagation crossing over the integral buckling arrestor were conducted,combined with the numerical simulation method,revealing the mechanism and characteristics of the propagation and its crossing over.Based on this,a better structure type the integral buckling arrestor was presented by hte topology optimization.In view of the previously neglected secondary buckling sensitivity factors: On the one hand,UOE forming process,which is commonly used in the manufacturing large diameter and thick-walled submarine pipeline,was simulated and analyzed to find out the correlation between the process and the buckling sensitivity factors according to the results.And then the theoretical method of the collapse pressure of thick-walled pipeline was modified,in order to quantitatively calculate the influence of the sensitive factors on the buckling performance of the pipeline.On the other hand,the dynamic pushover analysis for the pipeline span under the combined effect of the earthquake-pressure loading was conduted,and parameters sensitivity analysis such as water pressure,initial ovality amplitude,span length,diameter-thickness ratio,were carried out to study the impact of the complex load in the form of seismic on the collapse of pipeline.The results showed that the buckling failure modes and the seismic resistance behavior of the structure may be different and irregular.