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Research Papers: NDE

Toward An Ultrasonic Sensor for Pressure Vessels

[+] Author and Article Information
J. S. Sandman, B. R. Tittmann

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

J. Pressure Vessel Technol 130(2), 021501 (Mar 17, 2008) (5 pages) doi:10.1115/1.2892030 History: Received March 31, 2006; Revised February 05, 2007; Published March 17, 2008

The focus of this paper is an ultrasonic position indication system that is capable of determining one-dimensional target location in a high-temperature steel container with gaseous medium. The combination of the very high acoustical impedance of steel (45.4MRayl) and the very low impedance of a gas, for example, ambient air (0.0004MRayl), causes significant reflections at the interfaces. The strategy of this investigation was to develop an ultrasonic transducer capable of replacing a small portion of pressure vessel wall. In building such a transducer, acoustic matching layers for the steel-gas interface, a mechanically and acoustically competent housing, an efficient piezoelectric element, and appropriate backing materials are developed and tested. The results include a successful housing design, high- temperature acoustic matching layers, and subsequent successful wave forms with good signal-to-noise ratio. Target location through 9.6in.(24.5cm) of ambient air was possible, with a steel pressure boundary 0.456in.(1.160cm) thick, and the use of one matching layer. Our transducer was tested repeatedly to 340°C without apparent degradation. In addition to the experimental results, this investigation includes numerical simulations. Sample wave forms were predicted one dimensionally with the coupled acoustic piezoelectric analysis, a finite element program that predicts wave forms based on Navier’s equation for elastic wave propagation.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Sketch of system showing pressure vessel, target, transducer housing, and matching layer

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Figure 2

(a) CAPA simulation of pulse-echo wave form predicted for a piezoelectric element with a high-temperature plexiglas matching layer (b) Experimental pulse-echo wave form for a piezoelectric element with a high-temperature plexiglas matching layer

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Figure 3

Transducer housing

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Figure 4

Temperature dependence of sensitivity for selected piezoelectric materials. PZT is lead zinconate titanate (TC∼350°C); LN is lithium niobate (TC∼1250°C); PMN is lead metaniobate (TC∼570°C). Courtesy of Mahesh C. Bhardwaj and Mikel E. Langron, Ultran Laboratories, Inc., Boalsburg, PA.

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Figure 5

(a) Stainless steel housing with 1.5in. nose plexiglas matching layer (24.5cm air column, 1.5in. element) of PMN. Pulse height, 370mV; excitation voltage, 400V; gain, 60dB; attenuation, 0dB; damping, 500Ω; averaging, 15cycles; HP filter, 0.1MHz; LP filter, 0.5MHz. (b) Stainless steel housing with 1.5in. nose plexiglas matching layer (24.5cm air column, 1.5in. element) of PMN (expanded). Pulse height, 370mV; excitation voltage, 400V; gain, 60dB; attenuation, 0dB; damping, 500Ω; averaging, 15cycles; HP filter, 0.1MHz; LP filter, 0.5MHz.

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Figure 6

Oscilloscope traces (V versus μs) for signals from receiver with gain adjusted to keep signals approximately the same height. The transducer was mounted on a 25mm thick steel sample and tested in pulse-echo repeatedly to elevated temperature without significant degradation.

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