Ultrasonic Characterization of Cast Austenitic Stainless Steel Microstructure: Discrimination between Equiaxed- and Columnar-Grain Material – An Interim Study

Ultrasonic 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 due to detrimental effects upon the interrogating ultrasonic beam and interference from ultrasonic backscatter. The root cause is the coarse-grain microstructure inherent to this class of materials. Some ultrasonic techniques perform better for particular microstructural classifications and this has led to the hypothesis that an ultrasonic inspection can be optimized for a particular microstructural class, if a technique exists to reliably classify the microstructure for feedback to the inspection. This document summarizes scoping experiments of in-situ ultrasonic methods for classification and/or characterization of the material microstructures in CASS components from the outside surface of a pipe. The focus of this study was to evaluate ultrasonic methods and provide an interim report that documents results and technical progress. An initial set of experiments were performed to test the hypothesis that in-service characterization of cast austenitic stainless steel (CASS) is feasible, and that, if reliably performed, such data would provide real-time feedback to optimize in-service inspections in the field. With this objective in mind, measurements for the experiment were restricted to techniques that should be robust if carried forward to eventual field implementation. Two parameters were investigated for their ability to discriminate between different microstructures in CASS components. The first parameter was a time-of-flight ratio of a normal incidence shear wave to that of a normal incidence longitudinal wave (TOFRSL). The ratio removed dependency on component thickness which may not be accurately reported in the field. The second parameter was longitudinal wave attenuation. The selected CASS specimens provided five equiaxed-grain material samples and five columnar-grain material samples for a two-class discrimination problem. Qualitative TOFRSL estimates and a threshold algorithm classified all 10 material samples correctly and indicated a reliable and robust technique. Qualitative longitudinal wave attenuation estimates and a threshold algorithm also classified all 10 materials samples correctly; however, the technique was not as robust as TOFRSL. The experiments provided promising results and demonstrated that good potential exists for future development of techniques to implement real-time classification of CASS material. However, the reported measurements need to be substantiated with measurements on additional specimens

Prognostics and Health Management in Nuclear Power Plants: A Review of Technologies and Applications

This report reviews the current state of the art of prognostics and health management (PHM) for nuclear power systems and related technology currently applied in field or under development in other technological application areas, as well as key research needs and technical gaps for increased use of PHM in nuclear power systems. The historical approach to monitoring and maintenance in nuclear power plants (NPPs), including the Maintenance Rule for active components and Aging Management Plans for passive components, are reviewed. An outline is given for the technical and economic challenges that make PHM attractive for both legacy plants through Light Water Reactor Sustainability (LWRS) and new plant designs. There is a general introduction to PHM systems for monitoring, fault detection and diagnostics, and prognostics in other, non-nuclear fields. The state of the art for health monitoring in nuclear power systems is reviewed. A discussion of related technologies that support the application of PHM systems in NPPs, including digital instrumentation and control systems, wired and wireless sensor technology, and PHM software architectures is provided. Appropriate codes and standards for PHM are discussed, along with a description of the ongoing work in developing additional necessary standards. Finally, an outline of key research needs and opportunities that must be addressed in order to support the application of PHM in legacy and new NPPs is presented

Caracterización de materiales cementicios mediante la dispersión ultrasónica

Resumen Para determinar la durabilidad o vida útil de las construcciones de hormigón es necesario conocer la calidad y el estado de deterioro de los materiales cementicios. A nivel práctico, la caracterización más utilizada es la extracción de probetas o testigos y su análisis posterior en laboratorio. Sin embargo, la utilización de técnicas de evaluación no destructiva (END) presenta grandes ventajas sobre las técnicas habituales como poder conocer el estado de toda la estructura y permitir la monitorización en continuo de la misma. Entre los métodos de END, los ultrasonidos han demostrado su versatilidad para la caracterización de estos materiales tanto a nivel práctico como de investigación. El presente trabajo busca ahondar en el conocimiento de la interacción que se produce entre las señales ultrasónicas que se propagan a través de este tipo de materiales y su microestructura para poder determinar tanto la calidad como su estado. Para ello se aborda el efecto de la dispersión de las ondas ultrasónicas cuando se transmiten a través de los materiales cementicios, para establecer métodos y técnicas que permitan la caracterización de sus parámetros microestructurales tales como: la matriz cementicia, el tamaño y concentración tanto de los agregados y aire ocluido, entre otros. Para analizar como afecta la dispersión a las ondas ultrasónicas se ha desarrollado la extensión a N-fases del modelo dinámico autoconsistente. Este modelo, a diferencia de los hasta ahora utilizados, es capaz de predecir la dependencia de la velocidad y atenuación con la frecuencia de cualquier material multi-fásico con altas concentraciones de agregados. Asimismo, se han determinado las técnicas más adecuadas de inspección y de procesado digital de las señales ultrasónicas para medir de manera precisa la velocidad y atenuación en función de la frecuencia. Esta metodología se ha utilizado tanto para validar experimentalmente el modelo, como para caracterizar la microestructura de materiales cementicios a partir de las señales ultrasónicas. La validación experimental del modelo se ha realizado mediante la utilización de probetas de mortero de cemento. Para ello, se han comparado los resultados obtenidos mediante un estudio teórico y otro experimental de la influencia de los parámetros microestructurales más significativos sobre perfiles de velocidad y atenuación obtenidos por el modelo y medidos en probetas de mortero con diferente relación agregado/cemento y relación agua/cemento. Finalmente, se exponen la eficacia y limitaciones del modelo, así como también las técnicas desarrolladas para la caracterización de la microestructura de los materiales cementicios. Abstract The durability or lifetime of concrete buildings is related to the quality and the processes leading to the deterioration of cementitious materials. The most commonly used characterization techniques use cored samples that are analyzed in the laboratory. However, the application of non-destructive testing techniques (NDT) has significant advantages in comparison with other techniques. For instance, it is possible with the NDT approach to know the status of the entire structure and to perform continuous monitoring. Among NDT methods, ultrasonic techniques are successful in the characterization of cementitious materials. This work aims at providing further insight on the interaction between ultrasonic signals and the microstructure of such materials. Such interaction serves to determine the quality and status of concrete samples. Toward this end, ultrasonic scattering is addressed as ultrasonic waves travelling through heterogeneous materials. Several methods and techniques allow the characterization of the microstructural parameters of heterogeneous materials such as: cement matrix, particle size and volume fraction of both aggregates and air voids, among others. To analyze how scattering influences ultrasonic waves, an extension to N-phase of the dynamic self-consistent model has been formulated. Unlike the models commonly used, this model can predict the frequency dependence of both ultrasonic velocity and attenuation in any multiphase material with high concentrations of aggregates. This model was put in practice, and the most suitable techniques for inspection and digital signal processing were determined. The developed methodology was used for experimentally validating the model for characterizing the microstructure of cementitious materials from ultrasonic measurements. The model was tested experimentally using mortar cement samples with different aggregate/cement ratio and water/cement ratio. Theoretical results were compared with experimental data. Thus, microstructural parameter values were related to the velocity and attenuation profiles. Finally, the efficiency and the limitations of the theoretical model and the experimental techniques for the characterization of the microstructure of cementitious materials are discussed