Time domain trace of impulse hammer pulse recorded during the laboratory tests and (b) its corresponding frequency spectrum. Comparison of FE with test data (a) time domain signals and (b) corresponding frequency spectrum Comparison of FE and Lab test propagation characteristics (a) Wavenumber (b) Attenuation and (c) Phase velocity N1 N3 N2 Displacement signals and their corresponding FFT for pipe geometry and centre frequencies (a, b) 1 kHz (c, d) at 1.5 kHz and (e, f) 2.5 kHz Displacement signals and their corresponding FFT for pipe geometry and centre frequencies (a, b) 1 kHz (c, d) at 1.5 kHz and (e, f) 2.5 kHz Displacement signals and their corresponding FFT for pipe geometry and centre frequencies (a, b) 1 kHz (c, d) at 1.5 kHz and (e, f) 2.5 kHz Propagation characteristics at centre frequencies of 2.5 kHz (a) wavenumber (b) attenuation and (c) phase velocity as functions of frequency Attenuation of guided wave along a 12 in (305 mm) pipeline versus potential propagation distance at different centre frequencies Figure 5 (cd): Time and frequency domain displacement signals at 3 locations from (a, b) 6 in diameter pipe using 5 kHz centre frequency with 12 mm wall thickness and (c, Figure 10: Reflections from two inch diameter hole using 2.5 kHz centre frequencies (a) time domain signal and (b) corresponding spectrograph Long range guided waves for detecting holes in pipelines

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