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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

Madis Ratassepp, Sam Fletcher, Aleksander Klauson

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.

  1. Alleyne, D. N. and Cawley, P. Long range propagation of Lamb waves in chemical plant pipework. Mater. Eval., 1997, 55, 504–508.

  2. Alleyne, D. N., Pavlakovic, B., Lowe, M. J. S. and Cawley, P. Rapid, long range inspection of chemical plant pipework using guided waves. Insight, 2001, 43, 93–96.

  3. Alleyne, D. N., Lowe, M. J. S. and Cawley, P. The reflection of guided waves from circum­ferential notches in pipes. J. Appl. Mech., 1998, 65, 635–641.

  4. Demma, A., Cawley, P. and Lowe, M. J. S. The reflection of the fundamental torsional mode from cracks and notches in pipes. J. Acoust. Soc. Am., 2003, 114, 611–625.

  5. Lowe, M. J. S., Alleyne, D. N. and Cawley, P. The mode conversion of a guided wave by a part-circumferential notch in a pipe. J. Appl. Mech., 1998, 65, 649–656.

  6. Ratassepp, M., Fletcher, S. and Lowe, M. J. S. Scattering of the fundamental torsional mode at an axial crack in a pipe. J. Acoust. Soc. Am., 2010, 127, 730–740.

  7. Hayashi, T. and Murase, M. Defect imaging with guided waves in a pipe. J. Acoust. Soc. Am., 2005, 117, 2134–2140.

  8. Davies, J. and Cawley, P. The application of synthetic focusing for imaging crack-like defects in pipelines using guided waves. IEEE Trans. Ultrason. Ferroel. Freq. Control, 2009, 56, 759–771.

  9. Davies, J. and Cawley, P. The Application of synthetically focused imaging techniques for high resolution guided wave pipe inspection. In Review of Progress in Quantitative NDE (Thompson, D. and Chimenti, D., eds), (Plenum, New York, 2007), vol. 25, 681–688.

10. ABAQUS6.5. Analysis User’s Manual. Abaqus, 2004.
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