Analysis of Critical Suspended Span Length and Stress of Subsea Pipeline
Under the long-term effect of non-linear wave load,the seabed near the subsea pipeline in shallow water area is very susceptible to local scour erosion and transport,which will result in suspension and destabilization of the pipeline.To maintain the stability of subsea pipeline,the critical suspended span length of pipeline must be de-termined.The critical suspended span length is determined by using the wave force sustained by the suspended sec-tion of pipeline in shallow water area as calculated by the Morison formula and also the relation between the maxi-mum bending stress of pipeline and the allowable stress of the material.The material parameters are selected ac-cording to practical engineering,the law by which the suspended span length and wave parameter will affect the stress distribution of subsea pipeline is analyzed by using the Flac 3D numerical calculation software,and the varia-tion pattern of the correction factor k of mid-span bending moment is calculated.As the results indicate:the numeri-cal solution of the bending moment of the suspended structure is greater than the solution generated by the theoreti-cal formula,but as the suspended span length increases,the difference between the two solutions shows a trend of decreasing.With the same span length,the increase of wave height,decrease of wave length or increase of period will cause the deformation and maximum bending moment of pipeline to increase.As the span length increases,the maximum bending moment will move near the span end,which indicates that the failure point position of pipeline is related to the span length.The analysis result is used for analysis of practical cases,to provide the basis for identifying the failure of suspended pipeline and determining the timing of maintenance.
Subsea pipelineWave forceSuspended span lengthFlac 3D simulation analysis
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