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

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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.