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RESEARCH PAPERS

High Frequency Guided Wave Natural Focusing Pipe Inspection With Frequency and Angle Tuning

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

Department of Engineering Science & Mechanics, The Pennsylvania State University, University Park, PA 16802

J. Pressure Vessel Technol 128(3), 433-438 (Apr 20, 2005) (6 pages) doi:10.1115/1.2218348 History: Received January 21, 2005; Revised April 20, 2005

When ultrasonic guided wave nondestructive evaluation is used to inspect pipelines, partial loading of transducers around the circumference leads to a non-axisymmetric energy distribution. At particular axial distances and frequencies, the ultrasonic energy is naturally focused at some spots via constructive wave interference. This so-called “natural focusing” phenomenon can be used to improve guided wave sensitivity for a defect by impinging more energy onto it. However, defects located in other places can be missed, unless we can move the natural focusing points throughout the pipe. We have done this by frequency and circumferential angle tuning for specific circumferential loading lengths. In order to utilize the natural focusing phenomenon to enhance detection sensitivity, a frequency and angle tuning (FAT) technique is employed to extend the area that can be scanned by focal energy. It is observed that the natural focal points at a fixed axial distance move with frequency variation and circumferential excitation length change. In this paper, the natural focusing phenomenon with FAT is theoretically calculated and experimentally investigated. The results show that the natural focusing inspection technique can sufficiently inspect an entire pipe with FAT.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 6

Maximum amplitudes of axisymmetric and FAT natural focusing inspection results for the pipe #1. The defects include a 0.22% CSA five-hole cluster at 84in. and a 1.01% CSA RBH at 108in. from the pipe end A.

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Figure 7

Maximum amplitudes of axisymmetric and FAT natural focusing inspection results for the pipe #2. The defects include a 0.64% CSA RBH, a 0.76% CSA five-hole cluster at 94in. and a 1.01% CSA RBH at 110in. from the pipe end A.

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Figure 8

Schematic of ultrasonic transducer array locations and defect locations at the pipe #2, which is a 4in. schedule 40 steel pipe

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Figure 5

Experiment equipments, which include the Matec® commercial ultrasonic A-scan control system and the high frequency phased array on a 4in. schedule 40 pipe for 200–800kHz frequency tuning inspection.

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Figure 4

Schematic of ultrasonic transducer array locations and defect locations at the 4in. schedule 40 steel pipe

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Figure 3

Axial distance at z=82in., L(m,1) mode group angular profiles and their envelope over frequency range 200–800kHz in a 4in. schedule 40 steel pipe with the circumferential excitation angle (a) 45deg and (b) 90deg. The transducer is located at θ=0deg and z=0 (in.).

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Figure 2

Axial distance at z=106in., L(m,1) mode group angular profiles and their envelope over frequency range 200–800kHz in a 4in. schedule 40 steel pipe with the circumferential excitation angle (a)45deg and (b)90deg. The transducer is located at θ=0deg and z=0 (in.).

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Figure 1

(a) Phase velocity and (b) group velocity dispersion curves of 4in. schedule 40 steel pipe. There are six mode groups containing axisymmetric modes L(0,n) and flexural modes L(m,n), where n=1,2,…,6 and m=1,2,3,….

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