In-Line Nondestructive Inspection of Mechanical Dents on Pipelines With Guided Shear Horizontal Wave Electromagnetic Acoustic Transducers

[+] Author and Article Information
Xiaoliang Zhao1

 Intelligent Automation, Inc., 15400 Calhoun Drive, Rockville, MD 20855xzhao@i-a-i.com

Venugopal K. Varma

 Oak Ridge National Laboratory, Nuclear Science & Technology Division, Oak Ridge, TN 37831

Gang Mei, Bulent Ayhan, Chiman Kwan

 Intelligent Automation, Inc., 15400 Calhoun Drive, Rockville, MD 20855


Corresponding author.

J. Pressure Vessel Technol 127(3), 304-309 (Apr 06, 2005) (6 pages) doi:10.1115/1.1991879 History: Received February 28, 2005; Revised April 06, 2005

Circumferential guided ultrasonic Shear Horizontal (SH) wave Electromagnetic Acoustic Transducer (EMAT) pairs mounted on a mobile fixture in a through-transmission mode were used for detection and characterization of mechanical dents on the outer surface of a pipe wall from inside the pipe. The dents were created on a 12 in. diameter standard seamless steel pipe by hydraulically pressing steel balls of various sizes into the pipe wall. n1 mode SH wave was directed through and along the wall of the pipe. Multiple measurements were obtained both from the dents and from the no-flaw region of the pipe using the EMAT pair. Dent features were extracted with a Principal Component Analysis (PCA) technique and classified into “cup” and “saucer” types using Discriminant Analysis (DA). The overall approach is able to detect and classify dents of depth 25% through wall or deeper, which should meet the needs of the pipeline safety inspection community (U.S. Department of Transportation, Research and Special Program Administration). Preliminary dent depth estimation potential is also shown via an amplitude correlation approach.

Copyright © 2005 by American Society of Mechanical Engineers
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Figure 1

Circumferential SH wave dispersion curves in a 12 in. standard pipe

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Figure 2

(a) Principle of the Lorentz force SH wave EMAT and (b) SH EMAT probe designed for this study

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Figure 3

Three rows of cup and saucer dents created on a 7 feet long, 12 in diameter schedule 40 seamless pipe. They are 1 foot apart from each other or the pipe end for the same row.

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Figure 4

Sample “cup” and “saucer” dents created by a 0.75” and 5” diameter steel ball

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Figure 5

Diagram of the dent and the induced deformation

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Figure 6

EMAT configured inside the test pipe

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Figure 7

Sample waveforms of EMAT through-transmission signal from a normal pipe section, a cup dent, and a saucer dent

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Figure 8

Time domain correlation value for the normal condition, cup dents, and saucer dents. The first 90 samples are for normal conditions.

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Figure 9

Block diagram of the PCA-DA based classification method

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Figure 10

EMAT through-transmission signal amplitude versus the dent depth showing the overall decreasing signal strength with deeper dents. Saucer dents experienced a relatively sharper decrease compared to the cups. This information can be used inversely to estimate the dent depth after “cup” and “saucer” separation.




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