Corrosion thickness gauging in plates using Lamb wave group velocity measurements

Abstract

The use of guided waves in ultrasonic inspection of plate and pipe structures is faster but more complicated than conventional bulk wave inspection. This is due to dispersion effects and multimode propagation. This paper describes an ultrasonic measurement method allowing us to inspect the corroded thickness of plates using Lamb waves. This method consists of measuring the group velocity of the S 0 mode and then observing variations in velocity due to successive chemical attacks. From these data, it is possible to evaluate the progressively reduced thickness. Experimental and numerical results show that, depending on the chosen mode, the group velocity can be very sensitive to the reduction in thickness. Wavelet signal processing is suggested to extend this technique when several modes overlap.

Video Ultrasonics by Pulsed TV Holography: A New Capability for Non-Destructive Testing of Shell Structures

“…. The power density profile as a function of depth is mode-dependent, which allows tuning the flaw detection sensitivity peak to a certain location depth or to a given flaw morphology by a proper choice of the excited mode (Rose 2000, 419;Cho et al 1997;Jenot et al 2001;Lowe et al 1998;Pei et al 1996). .…”

Mode identification of broadband Lamb wave signal with squeezed wavelet transform

“…The Mexican Hat wavelet is a real wavelet, and it was used to measure the group velocity of the Lamb waves, so as to obtain the corrosion thickness in the plate [3]. The Mexican Hat wavelet was also used to analyze the signals generated by EMATs to identify the guided wave modes, for the tomography of artificial defects in the plate [4].…”

Robust helical path separation for thickness mapping of pipes by guided wave tomography

“…Within guided wave tomography, if multiple Lamb waves are excited and measured, rather than just using a single mode, they can overlap and approaches are needed to separate these out. Reference [4] suggested the use of wavelets to achieve this when time-based separation is not possible, however this only allows for the extraction of arrival times rather than the full wave signals; a similar wavelet technique was also investigated in [22]. A similar approach exploring the use of the discrete wavelet fingerprint (DWFP) technique for this problem is covered in [12], [23].…”