Numerical Simulation Of Corroded Pipes Under Complex Loads

Corrosion is one of the major reasons for the failure of steel pipe. Corrosion will cause pipe wall thin, which would result in the decrease of ultimate capacity and easy damage. To evaluate the residual strength of corroded pipe is the basis of assuring the pipe operation and determining whether the pipe needs to be replaced.Pipelines are applied to not only internal pressure, but also self-weight (pipe steel, protective coating, inner transportation medium, marine growth for subsea pipeline), supports from the surrounding soil, axial force induced by temperature change of inner medium, subsidence, landslide, wave effect subject to earthquake, axial force and bending moment under fault movement, impact load from dropped objects, drag and lifting force of free spanning submarine pipeline under waves and currents, and so on. Except that external pressure resulting in local collapse and buckling has to be taken into account for deep water pipeline, the mechanical model of pipeline subject to environmental loads can be described as the combinations of internal pressure, axial force and bending moment.The research of corroded pipe on burst capacity has been widely carried out. However, the studies of corroded pipeline on failure mode and residual strength under complex loads have been seldom performed.The numerical method is adopted to study failure mechanism of corroded pipeline under complex loads in this paper. Based on a practical subsea pipe in Shengli oil field, and considering material nonlinearity and geometric nonlinearity, three-dimensional finite element models of the corroded pipe under the combination of inner pressure, axial force and bending moment are established. Compared with the experimental and FE results, the FE model established in the paper is validated.Numerical analysis of corroded pipes under two kinds of load combinations such as internal pressure and bending moment, and axial force and bending moment are carried out. The effect of loading sequence for each load combination on ultimate capacity of the corroded pipe is studied. Meanwhile, the effects of the corrosion parameters including corrosion depth, corrosion width and corrosion length, geometric parameter such as the ratio of pipe diameter to wall thickness on limit strength and failure mode are analyzed.The study on corroded pipe under combined internal pressure, axial force and bending moment is fulfilled. The ultimate capacity interaction surfaces of the corroded pipe under the different loading sequences among the three loads are obtained. The effect of the different loading sequences on ultimate capacity is performed. The results show that loading sequences of a corroded pipe under internal pressure, axial force and bending moment has great effect on ultimate capacity and failure modes.