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RESEARCH PAPERS

A Natural Focusing Low Frequency Guided Wave Experiment for the Detection of Defects Beyond Elbows

[+] Author and Article Information
Joseph L. Rose, Li Zhang

Department of Engineering Science and Mechanics,  The Pennsylvania State University, 212 Earth Engineering Sciences Bldg., University Park, PA 16802

Michael J. Avioli

 FBS, Inc., 2134 Sandy Dr., Suite #14, State College, PA 16803

Peter J. Mudge

 Plant Integrity Ltd., Granta Park, Great Abington, Cambridge CB1 6AL UK

“TeleTest” is a trademark of Plant Integrity, Ltd UK.

J. Pressure Vessel Technol 127(3), 310-316 (Feb 21, 2005) (7 pages) doi:10.1115/1.1989350 History: Received January 14, 2005; Revised February 21, 2005

Long range ultrasonic guided wave inspection is advancing rapidly and is quite commonplace today. Benefits of using longitudinal or torsional modes are being established in special circumstances of improved sensitivity, resolution, or penetration power. The possibility of inspection under insulation, coatings, or with water filled pipes or around elbows is possible. Detection of defects beyond a pipe elbow is difficult for axisymmetric wave impingement onto the elbow. For nonaxisymmetric input to the elbow region, however, via partial loading around the circumference, natural focusing occurs because of angular profile variation around the circumference of the pipe. Sample computations of possible angular profiles are illustrated. An experiment is also reported here to demonstrate this inspection process.

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Copyright © 2005 by American Society of Mechanical Engineers
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Figures

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Figure 5

Angular profiles as a function of frequency for 45° circumferential length loading, on the top of the 4 in. schedule 40 steel pipe (−22.5° to +22.5°) at 57 in. as the L(0,1) guided wave enters the elbow region (also showing a superposition of the angular profiles by multiplexing eight regions around the pipe in (l), ensuring complete coverage at the elbow entry region

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Figure 6

Angular profiles as a function of frequency for 45° circumferential length loading, on the top of the 4 in. schedule 40 steel pipe (−22.5° to +22.5°) at 57 in. as the T(0,1) guided wave enters the elbow region (also showing a superposition of the angular profiles by multiplexing eight regions around the pipe, in (l) ensuring complete coverage at the elbow entry region)

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Figure 7

Initial experiment on detection of a defect beyond an elbow

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Figure 8

A portion of the segment of the subchannel B frequency scan echo responses

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Figure 9

Chart of echo response variation with frequency for subchannel B; maximum responses occurred at 85 and 86 kHz

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Figure 10

Echo responses before (a) and after (b) hole enlargement for the natural focusing experiment. The response (a) was obtained from a frequency scan and the background was replicated to enhance comparison.

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Figure 4

4 in. schedule 40 steel pipe phase velocity dispersion curves

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Figure 3

Location of ring transducer and subchannel designation

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Figure 2

Example of energy profiling in a straight pipe. The curve represents the magnitude of energy at the angular position shown

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Figure 1

4 in. Schedule 40 carbon steel elbow mockup with a TeleTest™ ring transducer (8 subchannels, 24 elements)

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