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Wavelet Transform Analysis of Guided Wave Testing on Coated Pipes

The torsional mode of guided wave, T(0,1), has been applied to detect discontinuities in pipelines, especially in the cases of coated, elevated and buried pipes. The signals of minor corrosions would be covered by the noise, unfortunately, because the coated material and buried medium always induce a strong attenuation of the guided wave. The main objective of this study was to discuss the effect of bitumen coating on guided wave tests by the experimental and signal processing techniques, based on the use of continuous wavelet transform. The experiments were first performed to collect the reflected signal of the discontinuities on two 152.4 mm steel pipes. The results showed that the bitumen coating seriously attenuated the signals of every discontinuity on the test pipes. The continuous wavelet transform was then used to perform a distance-frequency analysis in order to achieve the success of the minor discontinuity detection. In conclusion, the discussion of the effect of the bitumen coating on guided wave propagation and useful signal processing techniques will help to increase the sensitivity of discontinuity detection on coated pipe.

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