ESTONIAN ACADEMY
PUBLISHERS
eesti teaduste
akadeemia kirjastus
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Estonian Journal of Engineering

Axial defect imaging in a pipe using synthetically focused guided waves; pp. 66–75

Full article in PDF format | doi: 10.3176/eng.2011.1.07

Authors
Madis Ratassepp, Sam Fletcher, Aleksander Klauson

Abstract
Ultrasonic guided waves have been recognized as an effective tool for a rapid, long-range inspection of pipes. Still this technique has several difficulties in locating and quantifying defects properly due to the complex nature of guided waves. In this study a defect imaging technique is implemented to detect axially aligned defects in pipes. Imaging is necessary to locate the defect position and to improve the reflection coefficient from axially aligned defects, as the signals are very weak. The common source method of synthetic focusing has been applied, which makes it possible to determine information of the defect from the reconstructed image. By using data from finite element modelling, the dependence of the reflection coefficient on crack length was measured for both through thickness and part depth axially aligned defects at a range of frequencies, using the torsional guided wave family. The results show that the reflection coefficient is increased when focusing is employed, compared to unfocused fundamental torsional waves. However, the sensitivity is still very low, thus in practice this approach could only be used to find severe defects.
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