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In guided wave inspection for pipes, defect characterization is performed by echoes from defects. However, since detected signals become very complex due to mode conversion and multiple reflections, wave mechanics in a pipe with defects are not well studied. In this study, therefore, visualization technique for guided waves in a pipe is developed. In order to visualize guided wave propagation in a pipe, we need to scan an ultrasonic probe and measure ultrasonic waves at many points on a surface of a pipe. Position and posture of a laser doppler vibrometer are controlled by a robot arm, and ultrasonic vibration is detected at arbitrary points from arbitrary laser beam direction. Using the laser scanning technique, reflected guided waves from a shallow round defect was observed in the visualization results. From the defect, reflected waves propagated spirally in the oblique direction. From the view point of guided wave, the spiral waves were very high order modes that have not been measured in guided wave inspection. This result shows that such high order guided wave modes should be useful for defect characterization as well as low order modes. [ABSTRACT FROM AUTHOR]

An improved pulse compression technique was developed for long range testing using dispersive guided waves. This technique improves signal-to-noise ratio (SNR) of the guided wave signals and compensates for the wave distortion caused by dispersion characteristics of the guided wave. A fast calculation algorism was designed. It consists of integrations of both cross-correlation for pulse compression and compensation of velocity dispersion in wave number domain. Efficiency of the technique was verified experimentally, in which the results showed both spatial resolution and signal-to-noise ratio were improved. [ABSTRACT FROM AUTHOR]

Defects in a railhead and web can be detected with rail inspection cars and rail inspection tools equipped with special transducers such as wheel probes. However, bottom edges of rails, easily damaged regions due to contact to soil and fastening, are blind zones for the conventional ultrasonic inspection technique in which signals are input from a railhead. In this paper, inspection technique for defects in bottom edges of rails using guided waves were described. Dispersion curves for a rail obtained by a semi analytical finite element calculation show that a lot of propagating modes exist in a frequency region used for guided wave inspection, eg. 10kHz – 200kHz. Guided wave modes mainly vibrating a bottom edge of a rail were selected among the many modes in dispersion curves, and then defect detection tests were done using the selected modes. Good reflections from an artificial defect and a rail end were obtained with a vertically vibrating mode. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

Pipe screening technique with guided waves has become widely applied to pipe inspection in actual industrial plants. In most cases, however, guided wave propagating in a pipe is still difficult for inspection technicians due to its complex characteristics. Authors have developed the fast calculation technique for guided wave propagation using a semi-analytical finite element method (SAFEM). This study is on development of software for guided wave propagation with the SAFE calculation. A parameter input interface was made with Visual C++, and a core execution file was coded with Fortran 90. Visualization of data set obtained by the calculation was carried out with a free visualization tool OPEN DX. Using this software including a preprocessor and a postprocessor, many kinds of guided wave simulation have become feasible even by a non-expert in guided waves. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]