The use of circumferential guided waves (CGWs) for the inspection of pipe using in-line inspection tools is becoming more prevalent for such reasons as superior sizing estimation capabilities and the ability to detect stress corrosion cracking. A majority of the theoretical models used for the development of these detection and sizing techniques assume the pipe to be a fl at single-layer plate. This work removes these assumptions and specifi cally addresses wave propagation in a multilayer annular structure. Of specifi c interest are structures with a steel layer covered by a slower coating-like material. A parametric study is completed where the effects of coating thickness on shear-horizontal (SH) circumferential wave propagation are documented. The dispersion relation is considered for a multilayer annular structure and used to generate phase velocity and group velocity dispersion curves, as well as wave structures. Compared to the available library regarding axial wave propagation in pipe, the material available regarding circumferential wave propagation is relatively terse. Liu and Qu and Zhao and Rose were the first to present the dispersion solutions for Rayleigh-Lamb-type and shear-horizontal waves, respectively. Some applications involving circumferential guided waves (CGWs) include those developed by Valle et al. for crack detection and sizing, by Van Velsor et al. for coating disbond detection, by Hirao and Ogi for corrosion detection and sizing, and by Satyarnarayan et al. for pinhole detection and sizing in pipe support regions.

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