Research On Non-Destructive Testing Of Pipeline Defects With Different Structure Based On Ultrasonic Guided Waves

Pipelines are widely used in petroleum,chemical industry,nuclear power,natural gas,and urban construction.The entire pipeline system will contain multiple welds and elbows.For the entire pipeline system,welds and elbows are relatively weak parts.The working environment is harsh,and fatigue cracks and corrosion defects are extremely prone to cause pipeline leakage accidents.Ultrasonic guided waves can perform rapidly,large-scale,accurately,and low-cost inspections of pipelines,especially suitable for pipeline inspections where people cannot reach the environment,and are often used to detect defects in pipelines.Therefore,this article uses ultrasonic guided waves to perform non-destructive testing of different pipeline defects,and proposes the expansion method and the energy compensation method.The main research content of this article is as follows:(1)Choose the APDL interface of ANSYS as the platform for numerical simulation.First,establish the 3D solid model of the pipeline,combine the free meshing and the mapped meshing method,and then mesh the 3D model of the pipeline to establish the finite element model of the pipeline.In order to make the numerical simulation results more accurate,the Solid185 unit is selected under the premise of considering the time cost.According to the dispersion curve,the longitudinal mode L(0,2)guided wave is finally selected as the detection guided wave.(2)For single-welded straight pipes and double-welded straight pipes for single-defect weld detection,first determine the axial position of the weld through the time domain diagram,and then determine whether there are defects in the weld through the expanded method.For the problem of inconspicuous focus of guided wave energy for slot defects,the time reversal method is used to focus the guided wave energy near the defect,and then the circumferential position of the defect is determined by the expansion method.For doubledefect weld detection,first determine the circumferential position of the weld through the time domain diagram,and then identify whether there are defects in the weld through the expansion method,and determine the circumferential position of the defect.The defect reflection coefficient is selected as the standard for evaluating the sizes of defects in the weld.To verify the circumferential positioning of defects in single welded straight pipelines through experiments.(3)For 90° welded elbow inspection,the 90° welded elbow is divided into three areas:outside,side and inside.According to the displacement energy distribution cloud diagram of the guided wave propagating on the 90° welded elbow.The expansion method is used to detect the defects,in front of the elbow’s weld,and the modal separation method is used to detect the defects in the rear weld of the elbow;for the 90° direct elbow pipe,it is also based on the displacement energy distribution cloud diagram of the guided wave propagation.The90° direct bend pipe is divided into three areas for research.For the problem that it is not easy to detect the side defects of the straight pipe behind the elbow,the energy compensation method is used to detect the side area defects.Studies have shown that the combination of the expansion method and the time reversal method can detect weld defects on straight pipes.The expansion method and modal separation method can be used to detect weld defects before and after the elbow.The energy compensation method can be used to detect weld defects.The defect in the area beside the straight pipe after the elbow is effectively identified.There is a certain application reference value for the next step of using ultrasonic guided wave to detect crack defects in different structures of pipeline for the research of this paper.