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A Study on Dispersion Compensation of a Guided Wave in Pipes

To Kang · Sung-Jin Song

^∗

· Hak-Joon Kim

School of Mechanical Engineering, Sungkyunkwan University, Suwon 440-746 (Received 5 November 2010 : revised 29 November 2010 : accepted 17 January 2011)

For long-range nondestructive inspection of pipelines, ultrasonic guided waves are regarded as promising tools. However, dispersion of a guided wave in a pipe is a major drawbacks because dispersion makes interpretation of the signals from guided waves propagating through a pipe truly difficult. There are an infinite number of axisymmetric modes and a doubly infinite number of non-axisymmetric modes that are caused by the interactions of shear and longitudinal bulk waves with the boundaries of the pipes. The problem of dispersion can be relieved by using input signals with limited bandwidth. Even though the input signal consists of tone bursts that are limited in the bandwidth, received signals spread out in time, giving low resolution when the group velocity dramatically drops or increases. Therefore, in this study, to overcome these problems, dispersion compensation for guided waves was investigated to reduce the dispersive nature of guided waves.

-36-

To verify these methods, we performed experiments for an ASTM A106 6-inch schedule ]40 carbon- steel pipe with a circumferential notch embedded. Also, we introduced a signal compression ratio to estimate the amount of dispersion quantitatively as a function of the frequency bandwidth. In this paper, the principle of the signal processing methods and the dispersion compensation in pipes are discussed, and their performances are presented.

PACS numbers: 48.82.Et, 46.40.Cd, 42.30.Va

Keywords: Guided wave, Dispersion compensation, pipes

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∗E-mail: [email protected]

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Fig. 2. Schematic representation of application of dis- persion compensation algorithm.

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Defect type Parameters

Axial position from transducers (mm)

Circumferential position (

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Depth (%)

Axial length (mm)

Circumferential length (% of the whole circumference)

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