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Utilizing Normalized Correlation to Extract Meaningful Data From Noisy NDE Signals

[+] Author Affiliations
Douglas S. Shukert

Tohoku University, Sendai City, Japan

Paper No. PVP2005-71705, pp. 123-129; 7 pages
  • ASME 2005 Pressure Vessels and Piping Conference
  • Volume 5: High Pressure Technology, Nondestructive Evaluation, Pipeline Systems, Student Paper Competition
  • Denver, Colorado, USA, July 17–21, 2005
  • Conference Sponsors: Pressure Vessels and Piping Division
  • ISBN: 0-7918-4190-1 | eISBN: 0-7918-3763-7
  • Copyright © 2005 by ASME


Remote Induced Current Potential Drop (RICPD) is a nondestructive inspection method for finding cracks within stainless steel pipes. One problem with RICPD inspection is that the RICPD signal is very weak and is therefore, susceptible to being overshadowed by noise. Especially when trying to detect shallow cracks, the RICPD signal-to-noise ratio can be quite small, making signals from cracks indistinguishable from random signal noise. By using a mathematical filtering technique known as “normalized correlation” RICPD signals can be processed to extract meaningful data from noisy signals. Normalized correlation uses the signal waveform from a known crack as a model and compares that model waveform to every point of the RICPD test signal. All points that produce a match to the model are suspected cracks. Since normalized correlation does not depend on the magnitude of the signal or on the signal-to-noise ratio, even small cracks that produce nearly imperceptible signals can be detected. To successfully apply the normalized correlation algorithm, all that is needed is a model of the signal waveform from a known crack. The normalized correlation filtering technique has been successfully applied to 40mm thick blocks of stainless steel in the laboratory to detect underside man-made slits as shallow as 10mm.

Copyright © 2005 by ASME



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