Phased-Array Focusing with Longitudinal Guided Waves in a Viscoelastic Coated Hollow Cylinder

Abstract

Guided wave phased-array focusing techniques have been studied and applied in the longrange guided wave inspection of industrial pipelines. Advantages include longer inspection distance, greater wave penetration power and higher detection sensitivity. For reasons of protection, safety and thermal efficiency, a large percentage of pipes are coated and/or encased and buried underground. A phased-array focusing study for guided waves is now considered on pipelines with viscoelastic coatings. In this paper, longitudinal guided wave focusing as well as axisymmetric wave propagation is studied in a bare pipe and a pipe with a viscoelastic coating. A finite element model is studied. First, an investigation on whether the coating has an affect on the axisymmetric guided wave propagation is reported. Based on the result of a single channel, phased array focusing with 8-channel segments is studied. This study provides a very useful tool and guidance for the analysis and examination of guided wave focusing in a real field pipeline under various coating and environmental conditions.

The design and calibration of particular geometry piezoelectric acoustic emission transducer for leak detection and localization

“…The result agrees with the sensitivity directions of the two transducers to the wave motion. As shown in the dispersion curves of axisymmetric wave modes in Luo (2005), L(0, 2) wave mode (creating wave mode at the sensitive direction for the cut-PZT) has a wave velocity of about 5000 m s −1 and L(0, 1) wave mode (sensitive direction for the normal-PZT) has a wave velocity of about 2000-3000 m s −1 . Additionally, there is a significant change in velocity with a small variation in frequency in the range 20-100 kHz of the dispersion curve.…”

“…The sensor operates at thickness mode, sensitive to out-ofplane motion with respect to the propagating elastic waves. However, in cylindrical, plate-like geometries, this direction of sensing corresponds to the most dispersive longitudinal wave mode for frequencies less than 100 kHz, L(0, 1) (Luo 2005). In order to increase the discrete sensor spacing to monitor long pipeline structures, the transducers should be sensitive to tangential or in-plane motion with less attenuative characteristics, which corresponds to the longitudinal L(0, 2) mode.…”

Detection of Defects Using Spatial Variances of Guided-Wave Modes in Testing of Pipes

“…On the other hand, array processing techniques that use individual signals are generally used for imaging and focusing applications [21][22][23][24][25][26][27]. However, these algorithms are computationally expensive, and might require the individual excitation of transducers [26], or a phased-array focusing of the transducers [23], rather than synthetic focusing, where all of the transducers in the array are excited at the same time [21]. This adds to the complexity of the interpreting the results.…”