Pipeline Inspection Method Using Contact Torsional Guided Waves Based On Magnetostrictive Effects

Recently guided wave technology has been carried out widely because the technology can rapidly inspect over long distance from a single position. The contact torsional guided wave technique based on magnetostrictive effects has high energy coupling efficiency, which is suitable for long distance inspection and long-term monitoring. Based on the support of funds from National Key Technology R&D Program of China (No. 2006BAK02B03-S-01), this thesis studies the pipeline testing method based on contact torsional guided wave technique with magnetostrictive effects.Firstly, on the basic of the principle of torsional guided waves with magnetostrictive effects, the affects of magnetostrictive material, magnetization and coupling modes are analyzed, and the method for selecting transaudient material is proposed based on the model of acoustic wave reflection and transmission in multi-layer interface. The signal characteristics of bonding and dry coupling method using contact torsional guided waves are studied experimentally. The results reveal that the epoxy-guled bonding method has high efficiency, and the dry coupling method could be used repeatedly.Secondly, according to the non-dispersion characteristic of torsional guided waves, the unidirectional transmitting and receiving principles and methods for magnetostrictive guided wave are discussed based on space time transformation technique, and the specific implementation methodology is given. The setup of sensors for unidirectional inspection is given through analyzing the affect of the width and number of turns. The results show that the method could not only achieve unidirectional inspection, but also increase the signal-to-noise ratio, which is 3.8 times as much as that of bidirectional inspection.At last, the applications of contact magnetostrictive guided wave technique to flaw detection of pipelines are studied. The experiments of samples in the lab reveal that these methods could inspect artificial notch with 3.7% cross sectional area loss, while non-contact method couldn't. The results of field experiments indicate that the bonding method could test flaws over long distance, which could inspect the artificial blind hole and notch with 6% cross sectional area loss over 50 meters. The experiments of dry coupling method confirm that it could be used for not only ferromagnetic pipes, but also nonferromagnetic pipes. The results of comparison experiments with contact and non-contact magnetostrictive guided wave technique indicate that the coupling efficiency of the contact method is much higher than that of non-contact, which has wide application prospect in view of its high inspection sensitivity.