Finite Element Analysis And Research Of Submarine Pipeline With Double Corrosion Defects

Based on the significant impact on stress in the submarine pipeline by corrosion defects and severity of damage due to the corrosion defects, this paper aims at the injured pipeline with inside-pressure, and discusses issues related to pressurized pipeline with double corrosion defects and furthermore provides feasible solution to the stress level judgment in engineering making reference to research both home and abroad..In order to make certain the influence on the overall stress level of pipeline caused by two or more corrosion defects to the overall stress level of pipeline in relatively different location, finite element method (FEM) considering material and geometric nonlinearity is employed to analyze the change and influence of the stress concentration factor in an inside-pressured steel pipeline with two corrosion defects different in radial-angle and axis-distance. It is shown that the angle and the axis-distance are coupling parameters in stress concentration factor calculating. Therefore, a formula of "Critical Influence Distance" considering these two parameters is obtained through FEM analysis and curve fitting, which can be used in judging the possibility of defects interaction and then estimating the stress level of steel pipelines.A comparative analysis, considering different corrosion depths, is also carried out on the results obtained through stress concentration factor analysis and formula curve fitting of pipelines with similar defects. Meanwhile, finite analysis of equivalent stress of defective pipelines by ANSYS under the complicated loads (bending moments and inside pressure, axial stress and inside pressure) joint effect is conducted for its stress characteristics analysis, arriving at the relation of moments, axial stress and inside-pressure to equivalent stress.Stability analysis of pipeline in horizontal and vertical direction is adopted based on the static analysis of submarine pipeline. With the application of finite element method and considering the fluid-solid interaction phenomenon, modal analysis of pipelines, including non-damaged pipeline, pipeline with a single defect and double defects is carried out to educe the natural frequency and vibration mode, which could be used to determine the possibility of the pipeline resonance and destructional forms. Finite element method is used in the current paper to conduct the fatigue analysis of pipelines and the fatigue life of pipelines is therefore estimated.