Study On The Buckling Mechanism Of Submarine Pipes Under Tension And Pressure And The Crossover Of Arrestors

Submarine pipeline plays an important role in the field of marine engineering as the main transport carrier in the process of oil and gas development due to its characteristics of high efficiency,continuity and security,which is widely recognized by experts at home and abroad.These structures are normally subjected to combined loads from complex environment during installation,service and maintenance process,easily leading to buckling failure.The leakage of oil and gas resources caused by submarine pipeline buckling will result in catastrophic consequences.Therefore,study on the key scientific issues of failure mechanism of buckling,propagation and its arrest is conducted in this dissertation,which has practical engineering value.Theoretical model derivation and experimental research on the buckling of pipes under combined axial tension and external pressure are conducted.Considering the large deformation caused by pipe buckling,a theoretical model of pipes subjected to tension and pressure is established by deriving geometric equation,constitutive equation and energy equation.Moreover,computer programs are designed to solute these nolinear equations.Owing to the lack of relevant full-scale test data at home and abroad,especially for the case of combination between tension and pressure,the experimental procedure is designed in this dissertation.Full-scale and reduced-scale experiments of pipes are conducted based on the deep-sea pressure chamber.Correction of the theoretical model is verified by comparing the results of tests with the theoretical calculation.The effects of different loading paths on the collapse pressure of pipes are investigated by tests and numerical simulation.Different loading sequences are inevitable when pipes are subjected to tension and pressure.Experiments are conducted for the first time to study the effects of different loading paths on the collapse pressure of pipes with the same geometric and material parameters.The results of the experiments indicate that critical limit load of the P?T loading path is more severe than that of the T?P loading path.The determination of the dangerous path plays an important role in engineering application for checking the ultimate bearing capacity of pipes.The parameterized finite element model is established whose results are consistent with the experiments.The different effects of loading paths are explained by analyzing the stress distribution and ovalization of the local buckling section.Based on the FE analyses,a new interaction formula is proposed to estimate the limit loads of pipes for the P?T loading path.And the formula is more reasonable and verified by experiments comparing with the method proposed in DNV.Numerical simulation for the dynamic buckling propagation of pipes and crossover modes of arrestors are studied.the method of added mass element is adopted for simulation of fluid-structure interaction of dynamic buckling propagation of pipes.User element subroutine is designed in the finite element software considering the rate-dependent material constitutive relation which is corresponded to engineering practice of dynamic buckling propagation.Meanwhile,sensitivity analysis is carried out to study the effects of tension on dynamic buckling propagation.Different crossover modes including the flattening mode,flipping mode and other angle mode will occur when the integral arrestors of pipes are traversed.The influence of the initial ovality of the downstream pipe on the crossover modes of the integral arrestor is demonstrated for the first time by experiments and numerical simulation.Furthermore,the reason for the different crossover mode is explained.A more reasonable transformation factor for judging the flateening and flipping modes is proposed.Based on DNV specification,the formula of crossover pressure is modified with better accuracy.