In-Line Nondestructive Inspection and Classification of Mechanical Dents in a Pipeline with SH Wave EMATS

Circumferentially guided ultrasonic Shear Horizontal wave Electromagnetic Acoustic Transducer pairs in a through‐transmission mode were used for detection and characterization of mechanical dents on the outer surface of a pipe from inside. A mobile fixture with a resolver is designed for the EMAT probes so that the sensor positions and waveforms are recorded as the platform goes through the pipe. Safety critical “cup” dents and relatively benign “saucer” dents of 25% of wall thickness and deeper were successfully detected and classified with the n1 mode SH wave and a support vector machine classifier. Dent depth estimation is also possible with a signal energy correlation approach.