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Extracting Quantitative Information on Pipe Wall Damage in Absence of Clear Signals From Defect

[+] Author and Article Information
Amit Shelke

Department of Civil Engineering and Engineering Mechanics,  University of Arizona, Tucson, AZ 85721amitsh.iitk@gmail.com

Umar Amjad

Department of Civil Engineering and Engineering Mechanics,  University of Arizona, Tucson, AZ 85721; Institute of Experimental Physics II, University of Leipzig, Linnéstrasse 5, D-04103 Leipzig, Germanyumaramjad@email.arizona.edu

Milos Vasiljevic

Tribikram Kundu

Department of Civil Engineering and Engineering Mechanics,  University of Arizona, Tucson, AZ 85721tkundu@email.arizona.edu

Wolfgang Grill

Institute of Experimental Physics II,  University of Leipzig, Linnéstrasse 5, D-04103 Leipzig, Germanygrill@physik.uni-leipzig.de

J. Pressure Vessel Technol 134(5), 051502 (Sep 10, 2012) (11 pages) doi:10.1115/1.4005877 History: Received February 18, 2011; Revised November 18, 2011; Published September 10, 2012; Online September 10, 2012

It has been well established that guided waves are sensitive to structural damages encountered on their path of propagation and for this reason this technique is very efficient for distinguishing defective structural components from defect-free ones. Although the guided wave technique can identify a specimen having a distribution of defects, detecting and quantifying a small defect on its path from a long distance, as required for structural health monitoring (SHM) applications, is not an easy task for the guided wave inspection technique even today, especially when the transducers cannot come in direct contact with the pipe wall. The current technological challenges for pipe inspection by generating guided waves using noncontact transducers are to detect a small defect on the pipe wall and estimate its location and size from a long distance when the reflected signal from the defect cannot be clearly identified as is the case for low frequency guided waves that can propagate long distances. Electro-magnetic acoustic transducers (EMATs) are used here to generate guided waves in the pipe by the noncontact technique. This paper shows how small a defect in a pipe wall can be detected and its location and dimension can be estimated using relatively low frequency guided waves generated and received by EMATs even when the defect signal is not clearly visible in the time history plot because various wave modes reflected from the defect and pipe ends overlap.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of the experimental setup

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Figure 2

(a) Experimentally obtained time history plot for a defect-free pipe—different wave packets are numbered from 0 to 8; experimentally obtained time history plots generated by pipes with (b) 1 mm, (c) 3 mm, and (d) 5 mm holes

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Figure 3

Experimentally obtained time history plots in: (a) region 4 (or wave packet 4), (b) region 5 (or wave packet 5), (c) regions 6 and 7 (or wave packets 6 and 7), and (d) region 8 (or wave packet 8) for four pipes—one defect-free and three defective pipes

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Figure 4

Experimentally obtained time history plots for pipes with 1 mm, 3 mm, and 5 mm holes after subtracting the baseline signal (experimental data for the defect-free pipe). Bars marked 0–8 are identical to those shown in Fig. 2

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Figure 5

(a) Fourier transforms of wave packet 3, see time histories in Figs. 22; (b) Fourier transforms of wave packet 4, corresponding time histories are shown in Fig. 3; (c) Fourier transforms of wave packet 5, corresponding time histories are shown in Fig. 3; (d) Fourier transforms of wave packet 6, corresponding time histories are shown in Fig. 3; (e) Fourier transforms of wave packet 7, corresponding time histories are shown in Fig. 3; (f) Fourier transforms of wave packet 8, corresponding time histories are shown in Fig. 3

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Figure 6

Phase velocity (top) and group velocity (bottom) dispersion curves for the steel pipe

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Figure 7

Different paths of propagation of L(0,1) and L(0,2) modes in the defect-free pipe

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Figure 8

Vertical dotted lines denote arrival times of L(0,1) and L(0,2) modes going through different paths (shown in Fig. 7) in the defect-free pipe. Arrival times are shown on top of the recorded time history for the defect-free pipe

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Figure 9

Additional paths of propagation of L(0,1) and L(0,2) modes due to the presence of the defect in the defective pipe

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Figure 10

Vertical dotted lines denote arrival times of L(0,1) and L(0,2) modes generated due to the presence of the defect. Paths of propagation of these modes in the defective pipe are shown in Fig. 9. Arrival times are shown on top of the recorded time history for a defect-free pipe.

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Figure 11

Variations of the normalized spectral peak values of wave packets 6 and 7 as a function of the diameter of the hole. Note that for both wave packets the variation is monotonic—it is either increasing or decreasing.

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