A number of sensors have been designed and fabricated for pipeline inspection. These sensors use commercially available ultransonic tansuders but use a new coupling mechanism. Objective of these sensors is to generate Lamb wates, also known as the cylindrical guided waves in pipes. Some of these sensor require the presence of a computing fluid between the ultrasonic transduer and the pipe. These sensors can spect phosiontal pipes. Other sensors use solid compuling medium and can be used equally well for inspecting horizontal and vertical pipes. The coupling mechanisms have been designed such that different Lamb models in the pipe can be generated by changing the excitation frequency and includation angles of the transmitters. These Lamb wave sensors have been used to inspect a number of defect-free and defective pipes. The preliminary results show that theses Lamb wave sensors can detect the pripe defects even when the defects are located at a distance from the sensors. These experimental results along with the design of the new coupling mechanism are presented in this paper.
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