Development of Non-Contact Sensors for Pipe Inspection by Lamb Waves

本研究的主要目的是从理论上解释管道中不同类型的缺陷(凹坑、金属脱落和过切)所产生的实验结果，并利用这些知识开发一种非接触式管道兰姆波损伤检测传感器。在管道中产生弹性波的两种非接触方法是：1)激光激励和2)电磁声波换能器(EMAT)激励。虽然可以用激光在管道中产生和检测兰姆波，但这种方法对样品几何形状的微小变化非常敏感，不能在崎岖的野外条件下使用。这项研究的第一步是确定应该在管道中产生的Lamb模式，以检测有或没有保护层的完好和腐蚀管道中的特定类型的缺陷。将确定对缺陷最敏感、对管壁厚度变化最不敏感的Lamb模式。EMAT将被设计和制造来产生这种Lamb模式。一些样品将用这个装置进行测试。试件将包括四种常见的管材-钢管、铜管、铝管和非金属聚氯乙烯管。三种类型的有缺陷的试件将被制作成带有去除的金属、凿和凹痕的试件。这些缺陷的大小将不同，以实验研究不同兰姆模式的缺陷敏感性。即将开发的方法可以为目前工业常用的漏磁(MFL)方法提供一种替代(如果不是更好的方法)的方法。

The Main objective of this research is to theoretically explain the experimental results generated by different types of defects (dents, removed metal and gouge) in pipes and then use this knowledge to develop a non-contact sensor for inspecting damages in pipes by Lamb waves. The two non-contact methods for generating elastic waves in pipes are: 1) Laser excitation and 2) Electro-magnetic Acoustic Transducer (EMAT) excitation. Although it is possible to generate and detect Lamb waves in a pipe by laser beams, this method is very sensitive to small variations of the speciment geometry and cannot be used in rugged field conditioins. The first step of this research is to identify the Lamb modes that should be generated in the pipe to detect a specific type of defect in good and corroded pipes with or without protective coatings. The Lamb mode that is most sensitive to defects and least sensitive to the thickness variation of the pipe wall will be identified. EMAT will be designed and fabricated to generate this Lamb mode. A number of specimens will be tested with this device. The specimens will include four types of commonly available pipes-steel pipe, copper pipe, aluminum pipe and nonmetalic PVC pipe. Three types of defective specimens will be fabricated specimens with removed metal, gouge and dent. Size of these defects will be varied to experimentally investigage the defect sensitivity of different Lamb modes. The methods to be developed could offer an alternative if not a better approach to the current Magnetic Flux Leakage (MFL) method, which is commonly used by industries.