Gas Coupled Ultrasonic Measurement of Pipeline Wall Thickness

[+] Author and Article Information
Paul Shuttleworth, Julie Maupin, Albert Teitsma

 Gas Technology Institute, Des Plaines, IL 60018-1804

J. Pressure Vessel Technol 127(3), 290-293 (Mar 10, 2005) (4 pages) doi:10.1115/1.1991875 History: Received February 24, 2005; Revised March 10, 2005

Magnetic Flux Leakage (MFL) is currently the standard method of gas pipeline inspection in spite of the fact that the accuracy of MFL is only about 10%. Ultrasonic inspection has much better accuracy and is not sensitive to permeability changes but normally requires a liquid couplant to get sufficient energy into the pipe wall. Reported here are the laboratory results of Gas Technology Institute’s (GTI) effort to investigate newly developed transducers that use gas as the coupling media. The combination of transducers specifically designed for this application and high gain amplifiers produced signals strong enough to measure wall thickness in steel at pressures from 200 to 1000 PSIG. Investigations showed that both the sensitivity of the transducers and the gas-metal coupling are functions of pressure and, therefore, limit the useful pressure range. Tests were run in pulse-echo mode and pitch-catch mode to determine the advantages and limitations of each. The average ultrasonic wall thickness will be used to calibrate the MFL improving the accuracy of its measurements.

Copyright © 2005 by American Society of Mechanical Engineers
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Figure 1

Block diagram showing the experimental setup

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Figure 2

Pulse-echo waveforms taken at four different pressures

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Figure 3

Plot of peak-to-peak voltage of front surface reflection and back surface reflection signals as a function of pressure. (Note that the back surface signal is at a higher gain.)

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Figure 4

Plot of the ratio of the front surface to back surface reflected amplitudes as a function of pressure

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Figure 5

Waveforms showing the effect of using a bandpass filter to reduce fixed pattern noise

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Figure 6

Pulse-echo waveforms taken at different thicknesses

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Figure 7

Plot of the autocorrelation of the back surface pulse-echo reflections showing a peak at 3.2 microseconds

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Figure 8

Plot of the time for the peak in the correlation between two back surface reflections along a step block

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Figure 9

Pitch-catch waveforms taken at three different thicknesses

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Figure 10

Overlay of many pitch-catch signals at different thicknesses showing a peak at 5 microseconds and sensitivity dropping off for both thicker and thinner materials



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