Research On The Damage Mechanism Of Submarine Pipelines Under The Impact Of Falling Objects

In recent years,great progress has been made in the exploration and development of national marine oil and gas resources.Pipeline transportation has become the most important way of transportation of offshore oil and natural gas,the structural safety and operational reliability has received extensive attention.Due to the complexity of the marine environment,the failure of submarine pipeline will not only cause tremendous economic losses,but also catastrophic environmental pollution..At present,the main failure modes of submarine pipeline are mechanical disruption,corrosion and fatigue failure.The falling objects most likely cause mechanical damages in pipelines,such as anchoring,falling objects,fishing and so on.Therefore,the mechanical model of the impact of falling objects on submarine pipeline was established.And the mechanical response of the pipeline and the collapse mechanism of the defective pipeline were studied.The research results can provide the theoretical basis for the design,safety evaluation and maintenance of submarine pipeline.Based on the elastic-plastic mechanics,rock-soil mechanics,elastic ground beam method and finite element method,pipe-soil coupled numerical simulation model under various conditions was established.In this paper,the damage mechanism of submarine pipeline under the impact of falling objects was systematically studied:In the first place,a general introduction of the development trend and main failure forms of subsea pipelines were presented,and the feasibility and importance of the research on damage mechanism of submarine pipeline under the impact of falling objects were identified.And the research route of this paper was set.Secondly,the numerical calculation model of submarine pipeline under the impact of falling objects was established,and the effects of the foundation types and laying methods on stress-strain responses of submarine pipelines which has been hit were studied.Consequently,the results showed that the buried laying can protect effectively.Thirdly,mechanical effects of submarine pipeline under the impact of massive and beam fallings have been researched systematically.The effects of sensitive parameters,including impact velocity,impact angle,impact location,shape and size of falling objects,and the internal-external pressure difference and diameter-thickness ratio of pipeline on the mechanical behavior,damage mechanism and energy absorption of the pipeline were investigated.At length,the research of crushing mechanism of the submarine pipeline impacted by falling object were studied,5 crushing stage of submarine pipeline were analyzed,and the effects of diameter-thickness ratio and initial depression ratio of the pipe on the crushing pressure and buckling crushing deformation were discussed.