The Applied Physics group at the Pacific Northwest National Laboratory (PNNL) in Richland, WA has evaluated a
method for waterless/liquidless coupling of ultrasonic energy from planar ultrasonic contact transducers to irregular test
surfaces for ultrasonic non-destructive evaluation applications. Dry couplant material placed between a planar
transducer face and a curved or uneven steel or plastic surface allows for effective sound energy coupling and preserves
the integrity of the planar transducer sound field by serving as an acoustic impedance matching layer, providing good
surface area contact between geometrically dissimilar surfaces and conforming to rough and unsmooth surfaces. Sound
fields radiating from planar ultrasonic contact transducers coupled to curved and uneven surfaces using the dry coupling
method were scanned and mapped using a Pinducer receiver connected to a raster scanner. Transducer sound field
coverage at several ultrasonic frequencies and several distances from the transducer contact locations were found to be in
good agreement with theoretical beam divergence and sound field coverage predictions for planar transducers coupled to
simple, planar surfaces. This method is valuable for applications that do not allow for the use of traditional liquid-based
ultrasonic couplants due to the sensitivity of the test materials to liquids and for applications that might otherwise require
curved transducers or custom coupling wedges. The selection of dry coupling material is reported along with the results
of theoretical sound field predictions, the laboratory testing apparatus and the empirical sound field data.
A sound field beam mapping exercise was conducted to further understand the effects of coarse-grained microstructures
found in cast austenitic stainless steel (CASS) materials on phased array ultrasonic wave propagation. Laboratory
measurements were made on three CASS specimens with different microstructures; the specimens were polished and
etched to reveal measurable grain sizes, shapes, and orientations. Three longitudinal, phased array probes were fixed on
a specimen's outside diameter with the sound field directed toward one end (face) of the pipe segment over a fixed range
of angles. A point receiver was raster scanned over the surface of the specimen face generating a sound field image. A
slice of CASS material was then removed from the specimen end and the beam mapping exercise repeated. The sound
fields acquired were analyzed for spot size, coherency, and beam redirection. Qualitative analyses were conducted
between the resulting sound fields and the microstructural characteristics of each specimen.
Ultrasonic nondestructive examination (NDE) has a long and successful history of application across a wide array of
industries, including nuclear, aerospace, and transportation sectors. In coarse-grained, cast Manganese (Mn) steel frog
components, NDE/inspection challenges are encountered both in-field (after the frogs have been installed on a rail line)
and at the manufacturing facilities during post-fabrication QA/QC activities. Periodically inherently flawed frogs are
received from a manufacturer, and put into service, as most railroad operators do not have a means to conduct pre-service
examinations on received components. Accordingly, there is a need for a pre-service inspection system that can
provide a rapid, cost-effective and non-intrusive inspection capability for detection of defects, flaws, and other
anomalies in frog components, in order to avoid premature initiation of cracks or failures of these components during
service. This study focused on evaluating use of a volumetric phased-array ultrasonic testing (PA-UT) method to
monitor fabrication quality assurance. In this preliminary assessment of using PA-UT, data were acquired at a frequency
of 2.0 MHz on a known, flawed Mn steel frog component directly from a manufacturing facility. The component
contained flaws commonly found as a result of the manufacturing process of these cast rail components. The data were
analyzed and the anomalies were detected, localized and characterized. Results were compared against baseline
radiographic data. A detection metric was reported in the form of signal-to-noise values.
KEYWORDS: Signal to noise ratio, Ultrasonics, Signal processing, Inspection, Interference (communication), Acoustics, Scattering, Phased arrays, Data fusion, Laser scattering
Cast austenitic stainless steel (CASS) that was commonly used in U.S. nuclear power plants is a coarse-grained,
elastically anisotropic material. In recent years, low-frequency phased-array ultrasound has emerged as a leading
candidate for the inspection of welds in CASS piping, due to the relatively lower interference in the measured signal
from ultrasonic backscatter. However, adverse phenomena (such as scattering from the coarse-grained microstructure,
and beam redirection and partitioning due to the elastically anisotropic nature of the material) result in measurements
with a low signal-to-noise ratio (SNR), and increased difficulty in discriminating between signals from flaws and signals
from benign geometric factors. There is therefore a need for advanced signal processing tools to improve the SNR and
enable rapid analysis and classification of measurements. This paper discusses recent efforts at PNNL towards the
development and evaluation of a number of signal processing algorithms for this purpose. Among the algorithms being
evaluated for improving the SNR (and, consequently, the ability to discriminate between flaw signals and non-flaw
signals) are wavelets and other time-frequency distributions, empirical mode decompositions, and split-spectrum
processing techniques. A range of pattern-recognition algorithms, including neural networks, are also being evaluated for
their ability to successfully classify measurements into two or more classes. Experimental data obtained from the
inspection of a number of welds in CASS components are being used in this evaluation.
Maritime security personnel have a need for advanced technologies to address issues such as identification, confirmation
or classification of substances and materials in sealed containers, both non-invasively and nondestructively in field and
first response operations. Such substances include items such as hazardous/flammable liquids, drugs, contraband, and
precursor chemicals used in the fabrication of illicit materials. Our initial efforts focused specifically on a commercial
portable acoustic detector technology that was evaluated under operational conditions in a maritime environment.
Technical/operational limitations were identified and enhancements were incorporated that would address these
limitations. In this paper, application-specific improvements and performance testing/evaluation results will be
described. Such enhancements will provide personnel/users of the detector a significantly more reliable method of
screening materials for contraband items that might be hidden in cargo containers.
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