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Executive SummaryUltrasonic nondestructive evaluation (NDE) and inspection of cast austenitic stainless steel (CASS) components used in the nuclear power industry is neither as effective nor reliable as is needed. With current ultrasonic methods these limitations are in large part due to the detrimental effects of wavemicrostructure interactions on the interrogating ultrasonic beam and interference that results from ultrasonic backscatter. The root cause of these phenomena is the coarse-grain microstructure inherent to this class of materials. Some ultrasonic techniques are found to perform better for particular microstructural classifications and this has led to the hypothesis that an ultrasonic inspection can potentially be optimized for a particular microstructural class. For optimized ultrasonic technique selection, methods will be needed to reliably classify the microstructure in-situ, which is then used to guide the selection and optimization of the inspection. This document summarizes scoping experiments that investigate potential in-situ ultrasonic methods for classification and/or characterization of the material microstructures in CASS components, when making measurements from the outside surface of a pipe.The focus of this preliminary study was to evaluate ultrasonic measurement methods to determine if responses from different known microstructures can be differentiated and hence if in-service characterization of cast austenitic stainless steel (CASS) is potentially feasible. On the basis of an initial literature evaluation, two ultrasonic parameters, (i) the time-of-flight ratio between shear and longitudinal waves and (ii) the attenuation for normal incidence longitudinal waves, were selected for investigation. Scoping experiments were performed to determine the ability of these measured parameters to discriminate between different microstructures in CASS components. The objective was to determine if a more thorough and staged exploration would be justified in progressing toward the real-time characterization of CASS for use as feedback to optimize current or new ultrasonic in-service inspection methodologies. With this objective in mind, measurements were restricted to techniques that potentially should be robust if carried forward to an eventual field implementation.The first parameter investigated was a time-of-flight ratio of a normal incidence shear wave to that of a normal incidence longitudinal wave (TOFRSL). The ratio removes dependency on component thickness which may not be accurately known or reported in the field. The second parameter was the attenuation of a normal incidence longitudinal wave. The selected CASS specimens used for the experimental study were five equiaxed-grain material samples and five columnar-grain material samples, and these were used for a two-class discrimination problem.TOFRSL estimates and a threshold algorithm classified all 10 material samples correctly and indicated a potentially reliable and robust technique. Qualitative longitudinal wave attenuation estimate...

The attenuation of ultrasound through a kaolin–water slurry was measured for frequencies ranging from 0.5 to 3.0 MHz. The maximum concentration of the slurry was for a weight percentage of 44% (or a volume fraction of 0.24). The goal of these measurements was to assess the feasibility of using ultrasonic attenuation to determine the concentration of a slurry of known composition. The measurements were obtained by consecutively adding kaolin to the slurry and measuring the attenuation at each concentration. After reaching a maximum concentration a dilution technique was used, in which an amount of slurry was removed and water was added, to obtain the attenuation as a function of the concentration. The dilution technique was the more effective method to obtain calibration data. These measurements were carried out using two transducers, having a center frequency of 2.25 MHz, separated by 0.1016 m (4.0 in.). The maximum attenuation measured in these experiments was about 100 Np/m, but the experimental apparatus has the capability of measuring a larger attenuation if the distance between the two transducers is decreased. For a given frequency, the data show that ln V/V0 depends linearly upon the volume fraction (V is the received voltage for the slurry and V0 is that obtained for water). This indicated that each particle acts independently in attenuating ultrasound. The data showed that the attenuation is proportional to the frequency and to the volume fraction. The results demonstrated the feasibility of using attenuation measurements to determine slurry concentration. Several theoretical models are discussed that describe the attenuation of ultrasound. The data obtained by several other researchers also show a linear dependence of attenuation upon frequency.

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