A fundamental torsional mode of guided waves, T(0,1), has recently become more widely used to reduce the time and cost involved in long-range pipe testing. Many pipes of interest in the refinery and petrochemical industries are supported with welded support brackets; the reflected signals, with trailing echoes, from these welded supports affect the ability to perform discontinuity detection at the supports and the testing range is seriously diminished when using the guided wave technique. The effect on guided wave propagation of a support bracket welded onto a 152 mm steel pipe is investigated by both experimental and simulative techniques in this paper. The experiments were first performed to collect the reflected signal from the welded support bracket. The results showed not only that the peak of the received signal lagged behind the actual position of the support, but that the enduring signal from the welded support covered up the discontinuity signals beyond the support at low frequency. The mode conversion phenomenon and the frequency-dependent behavior of the reflected signal were then examined using the finite element method.
The response spectra of the reflection had a localized maximum value of around 21 kHz, both from the experimental and simulative results. It can be seen that the constructive interference of the A0 mode inside the support bracket caused the localized maxima response by comparing the mode shapes of different frequencies. From the transient analysis results, the interactions between the T(0,1) mode and the support bracket in the pipe (including the reflection, the transmission and the leakage) were shown. In summary, good agreement is obtained between the experimental and simulative results. Discussing the effect of the support bracket on guided wave propagation aids in discontinuity detection by providing a better understanding of the interaction between the guided wave and the pipe features.
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