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Development of an EMAT System for Detecting flaws in Pipeline  

Ahn, Bong-Young (Smart Measurement Group, Korea Research Institute of Standards and Science)
Kim, Young-Joo (Smart Measurement Group, Korea Research Institute of Standards and Science)
Kim, Young-Gil (Smart Measurement Group, Korea Research Institute of Standards and Science)
Lee, Seung-Seok (Smart Measurement Group, Korea Research Institute of Standards and Science)
Publication Information
Journal of the Korean Society for Nondestructive Testing / v.24, no.1, 2004 , pp. 15-21 More about this Journal
Abstract
It is possible to detect flaws in pipelines without interruption using all EMAT transducer because it is a non-contact transducer which can transmit ultrasonic waves into specimens without couplant. And it ran easily generate guided waves desired in each specific problem by altering the design of coil and magnet. In the present work, EMAT systems have been fabricated to generate surface waves, and selectively the plate wave of $A_1\;or\;S_1$ mode. The surface wave of 1.5MHz showed a good signal-to-noise ratio without distortion in its propagation along a pipeline, while the $S_1$ mode of 800kHz and the $A_1$ mode of 940kHz were distorted according to their dispersive properties. The wider the excitation pulse becomes, the better the mode selectivity of the plate waves becomes. A pipe of 256mm inner diameter and 5.5m thickness with 5 flaws was used for comparing the flaw detectability among the modes under consideration.
Keywords
EMAT; pipeline; guided wave; surface wave; plate wave;
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