Propagation Of Guided Waves In Pipeline Structure Surrounded By Water

With the development of ultrasonic guided waves technique, more and more applications are undergoing to inspect the damages and defects of seabed oil pipeline. However, there is still initial stage in China. The most important step for health monitoring and defect inspecting by the ultrasonic guided waves is to study the law of guided waves propagation in seabed pipeline structure.In the paper, the propagation theory and research methods are firstly introduced. Then the displacement and stress of seabed pipeline structure as guided wave propagating are calculated by a global matrix method and frequency dispersion equations are deduced by considering the boundary conditions. The frequency dispersion analysis are conducted for the monolayer pipeline, pipeline with viscoelastic layer, pipeline under water loading, pipeline full of viscous liquid, viscoelastic enveloped pipeline full of viscous liquid surrounded by water and seabed oil pipeline. The corresponding axial-symmetry guided waves are plotted, including longitudinal and torsion modes.By comparison of the frequency curves and wave configuration of those pipeline structures, the propagation characteristics are explained in details and the effects of water loading, viscoelastic medium and oil on the guided waves are analyzed. The results can help to clear the propagation waves of seabed pipelines and provide technique ability for inspecting the damage of the seabed pipeline by the longitudinal guided waves.At last, a combined solution of boundary elements method (BEM) with mode extended technique (NMET) is introduced to solve the guided wave dispersion of a plate including six type of defects, such as a free boundary, inclined boundary, defect boundary, surface triangle defect, surface rectangle defect and inner defect. The interactions of guided wave on those defects are analyzed to explain the ability and advantage of the solution. The numerical results are beneficial to the selection of mode and frequency for engineering applications, the identification of defects and the quantitative analysis of defect size.