Research On Residual Ultimate Strength Of Damaged Submarine Pipeline

Submarine pipeline plays an important role in the development of offshore oil and gas industry so that its safety and reliability have been widely concerned.In case the pipeline failure happens,it may cause huge economic losses and serious ecological damage.Both environmental factors and human factors may cause damages on the surface of submarine pipelines.The occurrence of damages reduces the ultimate capacity of pipelines,then increasing the probability of pipeline failure.Damages on pipelines is one of the main reasons for pipeline failure.Dents,notches and cracks are common types of damages on the pipes.No matter in installation phase or operation phase,pipelines are subjected to large bending loads.Bending failure is one of the main forms of pipeline failure.Therefore,it is important to research the ultimate strength of damaged pipelines under bending moment.In the present paper,collapse test and finite element analysis are combined to research the residual ultimate strength of damaged seamless steel pipes with an out diameter of 168 mm and a thickness of 8mm under bending moment.The conclusions obtained from the present research can provide basis for a comprehensive safety assessment criteria of damaged pipeline.Main works can be summarized as follows:1)A test scheme for residual ultimate strength of series damaged pipeline was made.The types of damages include dents,notches and cracks,both single damage and combined damages in compression side or tension side were considered.2)Collapse tests of 4 intact pipes and 26 damaged pipes under bending moment were carried out.To clarify the mechanical properties of materials,tensile test of some material sample from pipes was conducted.The ultimate bending moment,failure mode and moment-curvature relationship curve of each pipe were obtained from the experiment.3)A series of nonlinear finite element analysis were carried out to simulate structural behavior of damaged pipes under bending moment by ABAQUS.The discrepancy between test and simulation result was discussed,according to test and simulation result,the ultimate bending moment,failure mode and moment-curvature relationship of pipes with different damages or combined damages were clarified;4)By changing the parameters of each damage,a series of numerical simulations were carried out.The influence of length,width and depth of different damages on the ultimate strength of pipes was investigated.