Studying On Ultrasonic Guided Wave Pipeline Inspection Based On Synthetic Focusing Technique

Due to its economic, security, efficiency, the pipeline, which is known as theindustrial main artery, is wildy used in modern industry. As the development of theindustry, the total length of the industrial pipeline in our nation is growing. Defectssuch as corrosion and crack may occur in the in-service pipeline because of thenatural aging and environmental corrosion, and bring a huge security risk for thepipeline transportation. At present, the detection and location of defects becomespriority of the research on pipeline inspection. Therefore, the research on pipelineinspection technology is more and more important, especially the detection of minordefects.High efficiency and long range is the main advantage of the ultrasonic guidedwave technology, which makes it the most popular technology in pipeline inspection.In the current research, a pipeline inspection method based on synthetic method anddirection control method has been proposed in order to locate the defects. Synthetictime-reversal method and synthetic phase-control method have been proposed in orderto improve the capability of ultrasonic guided wave inspection as well. The efficacyof these method is proved through FEM simulation and experiments.The mainresearch works are given as follows.(1) The process of the sensor array, including synchronized excitation, defectreflection and synchronized receiving, is analyzed using a transfer function method.The final result of the multi-channel synchronous excitation–receiving is replaced bythe sum of a set of single-channel excitation-receiving signals. The effectiveness ofthe method is proved through FEM simulation and experiments.(2) Based on the synthetic method, a completely post-acquisition signalprocessing method is proposed to control the inspection direction. Using signalscollected by2transducer rings placed on the pipeline and a single-channel excitation–receiving system, the defect reflections from different direction are separated and the defects are located. This method is proved to be effective by FEM simulation andexperiments.(3) Based on a large number of experimental results, signals of some pipestructures such as flanges and welds are collected to build the sample database. Basedon this database, the signals of those pipe structures can be automatically identifiedfrom the inspection result using a identification method based on correlation analysisand support vector machine.(4) Combined with synthetic method, the time-reversal method is developed intoa completely post-acquisition focusing method named synthetic time-reversal method.FEM simulation and experiment prove that this method is as effective as theconventional time-reversal method but only requires a much easier single-channelsystem.(5) Combined with synthetic method, the phase-control method is developed intoa completely post-acquisition focusing method based on single-channel system, whichis named synthetic phase-control method. FEM simulation and experiment prove thatthis method is able to improve the detection capability and locate the defects in bothaxial and circumferential direction.