Non-Destructive Testing of industrial components carries vital importance, both financially and safety-wise. Among all Non-Destructive techniques, Long Range Ultrasonic Testing utilizing the guided wave phenomena is a young technology proven to be commercially valid. Owing to its well-documented analytical models, Ultrasonic Guided Waves has been successfully applied to cylindrical and plate-like structures. Its applications to complex structures such as multi-wire cables are fairly immature, mainly due to the high complexity of wave propagation. Research performed by the author approaches the long range inspection of overhead transmission line cables using ultrasonic guided waves. Existing studies focusing on guided wave application on power cables are extremely limited in inspection range, which dramatically degrades its chances of commercialization. This thesis consists of three main chapters, all of which approaches different problems associated with the inspection of power cables. In the first chapter, a thorough analysis of wave propagation in ACSR (most widely used power cable) cables is conducted. It is shown that high frequency guided waves, by concentrating the energy on the surface layers, can travel much further in the form of fundamental longitudinal wave mode, than previous studies have shown. Defect detection studies proved the system’s capability of detecting defects which introduce either increase or decrease in cross sectional area of the cable. Results of the chapter indicate the detectability of defects as small as 4.5% of the cross sectional area through a 26.5 meter long cable without any post-processing. In the second chapter, several algorithms are proposed to increase the inspection range and signal quality. Well-documented wavelet-denoising algorithm is optimized for power cables and up to 24% signal-to-noise ratio improvement is achieved. By introducing an attenuation correction framework, a theoretical inspection range of 75 meters is presented. A new framework combining dispersion compensation and attenuation correction is proposed and verified, which shows an inspection range of 130 meters and SNR improvement up to 8 dBs. Last chapter addresses the accurate localization of structural defects. Having proven the optimum excitation and related wave propagation in ACSR cables, a system having a more complex wave propagation characteristics is studied. A new algorithm combining pulse compression using Maximal Length Sequences and dispersion compensation is applied to multi-modal signals obtained from a solid aluminum rod. The algorithm proved to be able to improve signal quality and extract an accurate location for defects. Maximal Length Sequences are compared to chirp signals in terms of SNR improvement and localization, which produced favourable results for MLS in terms of localization and for chirp in terms of SNR improvement.

A tomografia ultrassônica é um método não destrutivo que possibilita o mapeamento de uma seção interna do objeto estudado a partir de múltiplas projeções de resultados de ensaios de ultrassom a fim de identificar algumas de suas propriedades físicas, descontinuidades e/ou defeitos. Este trabalho consiste em estudar o método da tomografia ultrassônica aplicada na detecção de não homogeneidades em elementos de concreto. Para tal fim, realizaram-se diversos ensaios experimentais em prismas de concreto variando-se parâmetros como a qualidade do concreto, presença de vazios e armaduras, o arranjo dos transdutores, a frequência e a polarização das ondas ultrassônicas. Além dos ensaios, foi desenvolvida uma aplicação computacional que permitisse gerar imagens tomográficas de várias seções do elemento estudado, em diferentes planos e profundidades simultaneamente, a partir das velocidades de propagação dos pulsos de ultrassom. Como resultado conseguiu-se determinar as condições mais confiáveis nos procedimentos de medição, avaliar o grau de homogeneidade de prismas com diferentes resistências e avaliar a sensibilidade dos ensaios de ultrassom na presença de não homogeneidades como vazios, fissuras e aço de reforço. Finalmente, como conclusão desta pesquisa confirma-se o grande potencial que possui a técnica de tomografia ultrassônica aplicada em estruturas de concreto na detecção de não homogeneidades. / Ultrasonic tomography is a non-destructive method that enables the mapping of an internal section of the object studied from multiple projections of results of ultrasound tests to identify some of their physical properties, discontinuities and/or defects. This work is to study the method of ultrasonic tomography applied to the detection of inhomogeneities in concrete elements. To this end, there have been several experimental tests on concrete prisms varying parameters such as the concrete quality, the presence of voids and reinforcement, the arrangement of the transducers, the frequency and polarization of the ultrasonic waves. In addition to the tests, a computer application was developed that allows to generate tomographic images of various sections of the study element and depths in different planes simultaneously from the propagation speed of the ultrasonic pulses. It was possible to determine the most reliable conditions in the measuring procedures to assess the degree of homogeneity of prisms having different resistances and to evaluate the sensitivity of ultrasound tests in the presence of inhomogeneities such as voids, cracks and reinforcing steel. Finally, as a conclusion of this research confirms the great potential that has the ultrasonic tomography technique applied in concrete structures in the detection of inhomogeneities.

Les Essais Non Destructifs (END) par ultrasons permettent de caractériser le béton, sans le dégrader en raison de leurs liens avec ses propriétés mécaniques et sa composition. Cependant, les signaux mesurés résultant de diffusions successives et multiples des ondes sont complexes à analyser. Afin d’optimiser les techniques ultrasonores, il est nécessaire de mieux comprendre les interactions onde-matière dans ce type de milieu et de modéliser au mieux les phénomènes associés. Afin d’aller au-delà des limites des modèles analytiques d’homogénéisation, dans ce travail de thèse un modèle numérique bidimensionnel décrivant la propagation d’ondes ultrasonores dans un milieu hétérogène, adapté au béton, est construit dans le logiciel SPECFEM2D. Ce modèle est comparé à des modèles analytiques, et validé expérimentalement à l’aide d’un milieu synthétique à forte hétérogénéité en comparant les deux paramètres effectifs cohérents : vitesse de phase et atténuation. Il permet également de prendre en compte la viscoélasticité du mortier par l’intermédiaire d’un facteur de qualité. Celui-ci est déterminé à partir des mesures effectuées pour une série de mortiers étudiés.L’outil numérique complet peut être utilisé à plusieurs fins: d’une part, la réalisation d’études afin d’évaluer l’influence de certains paramètres sur la propagation d’onde (la forme et la distribution des granulats), et d’autre part, la simulation des configurations de mesure mises en œuvre sur structure afin de les optimiser en fonction des paramètres qui interviennent, en particulier la fréquence des ondes. Cette meilleure maîtrise des mesures permettra de conduire à terme à l’amélioration du diagnostic. / Ultrasonic non-destructive testing (NDT) is used to characterize concrete, without degrading it, because of its relationship to its mechanical properties and composition. However, the measured signals resulting from successive diffusions and thus from multiple scattering are therefore complex to analyze. In order to optimize ultrasonic techniques, it is thus necessary to better understand the wave-material interactions in this type of medium and to better model the associated phenomena. In order to go beyond the limits of analytical homogenization models, in this thesis a two-dimensional numerical model describing the propagation of ultrasonic waves in a heterogeneous medium, adapted to concrete, is built in the SPECFEM2D software package. This model is compared to analytical models, and validated experimentally using a synthetic medium with high heterogeneity by comparing the two effective parameters of coherent waves: phase velocity and attenuation. This numerical model also makes it possible to take into account the viscoelasticity of the mortar by means of a quality factor. This quality factor is determined from measurements made for a series of mortars that we study. The complete set of numerical tools developed in this work can be used for several purposes: firstly, to carry out studies to evaluate the influence of certain parameters on wave propagation (the shape and distribution of aggregates), and secondly, the simulation of the measurement configurations implemented for a structure in order to optimize them in terms of the parameters involved, in particular the wave frequency. This better control of the measures will ultimately lead to better diagnosis.

Ground penetrating radar (GPR) technology has existed for many decades, but it has only been in the last 20 to 30 years that it has undergone great development for use in near surface ground investigations. The early 1980's saw the first major developments in the application of GPR for pavements (i.e. engineered structures designed to carry traffic loads), and it is now an established investigation technique, with generic information included in several national standard guidance documents. Analysis of GPR data can provide information on layer depths, material condition, moisture, voiding, reinforcement and location of other features. Assessing the condition of pavements, in order to plan subsequent maintenance, is essential to allow the efficient long-term functioning of the structure and GPR has enhanced and improved the range and certainty of information that can be obtained from pavement investigations. Despite the recent establishment of the technique in pavement investigation, the current situation is one in which GPR is used routinely for pavement projects in only a minority of countries, and the specialist nature of the technique and the sometimes variable results that are obtained can mean that there is both a lack of appreciation and a lack of awareness of the potential information that GPR can provide. The fact that GPR is still a developing technique, and that many aspects of its use are specialised in their nature, means that there are also several technical aspects of GPR pavement investigations which have not been fully researched, and knowledge of the response of GPR to some material conditions has not been fully established. The overall aim of this EngD research project was to provide improved pavement investigation capabilities by enhancing the methodologies and procedures used to obtain information from GPR. Several discrete research topics were addressed through various research methods including a literature review, fieldwork investigations, experimental laboratory investigations and a review of previously collected data. The findings of the research allowed conclusions and recommendations to be made regarding improved fieldwork methodologies, enhancing information and determining material condition from previously collected GPR data, assessing the effect of pavement temperature and moisture condition on GPR data and also on managing errors and uncertainty in GPR data. During the EngD project, a number of documents and presentations have been made to publicise the findings both within the EngD sponsoring company (Jacobs) and externally, and an in-house GPR capability has been established within Jacobs as a direct result of the EngD project.

Concrete structures are susceptible to deterioration over time and it is vital to continually assess concrete structures to maintain the structural integrity and prolong the service life. In recent years there has been an increased interest in non-destructive testing of concrete, i.e. assessing the state of the concrete without causing any damage to the structure in the process. There are many different techniques that falls under the term non-destructive testing and one of these that have gained prominence during the last few years is Georadar or ground penetrating radar, often shortened as GPR. GPR is a technique where microwaves are sent into the surface of the concrete by a device, the waves will reflect back to the device when encountering interfaces of areas with different electric properties. The waves are then received by the same device indicating the internal structure of the concrete. This makes the technique an excellent way to find reinforcement bars as the electric properties of concrete and metal strongly differ. In theory though, the technique should also be able to detect other internal differences in concrete, such as voids and corrosion areas but further research is still needed in these areas. This aim of this report is to evaluate ground penetrating radar as a non-destructive technique for assessment of concrete structures. In order to do this different tests has been conducted to evaluate the general performance and usability with a literature review introducing the science behind and what conclusions other researches has reached and using a testing methodology to reach the results. The tests can in a simple way be divided into two parts, first lab tests on a slab in a controlled setting where the internal structure was known, and then two shorter field trips in order to evaluate the performance properly insitu. The results were, to some extent, ambiguous. Although it was found that GPR is an excellent method for finding and locating near-surface reinforcement it was also concluded that the results could vary significantly depending on the location. In one of the field trips the performance of the GPR technique was compared to the performance of traditional cover meter and in this case the portability of the cover meter outperformed the somewhat clunky handling of the GPR. The concrete cover measurement using post-processing of the radar data gave a rough estimate, but once again evaluation still relied on the insitu conditions and the estimate were sometimes questionable. Finding reinforcement below the first layer yielded differing results and it was concluded that further tests were needed to fully evaluate the capabilities of the technique in this regard. The conclusions of the thesis was that although the tests show some potential for the method the results expected from GPR would strongly depend on suitability of the project and experience of the user. One important limiting factor was the availability of devices. For the current project only one specific device was used, it was theorized that another GPR device could get better results depending on the purpose. Furthermore, the lack of experience was also considered to be a limiting factor that might have had an effect on the results. For future research more tests on lower reinforcement and tests on detection of deterioration were suggested. Comparative studies with other similar non-destructive techniques were also considered to be an area of possible interest.

Sistemas de ensaios não destrutivos por ondas guiadas despertam cada vez mais a atenção tanto da indústria, como da academia. Isso deve-se, principalmente, às possibilidades que as ondas guiadas permitem, como maior área de triagem que o ultrassom convencional. Porém a técnica tem suas limitações, já que esta apenas gera uma estimativa da localização de um defeito e não a sua dimensão. Nessa limitação, algoritmos tomográficos apresentam uma possibilidade de avanço da técnica, pois permitem determinar não só a localização de corrosões e defeitos, mas também seu dimensionamento. Este trabalho apresenta tomografia de difração como uma alternativa para avaliação de integridade estrutural. Primeiramente, utilizou-se análise por métodos numéricos para mostrar a validade dos algoritmos e posteriormente foi realizado um experimento em uma chapa real com o objetivo de reconstruir a imagem do defeito. / Guided waves nondestructive testing systems are increasingly attracting industrial and academic attention. The mainly reason for this attention is the possibility of screening a large area than conventional ultrasound technique. However, Guided Waves Testing has limitations, since it gives only an estimation of the location of a defect, but not the dimensions. Tomographic algorithms come up with an improvement of the technique, because it allows discovery not only the location of corrosions and defects, but the dimensions too. This work brings Diffraction Tomography as an alternative to structural health monitoring. First, a numerical analysis was implemented to demonstrate the validity of the algorithms, after that an experiment in a real plate was made with the objective to recover the defect image.

A operação segura e eficiente em unidades de produção de petróleo e gás depende do desempenho de seus dispositivos, componentes e estruturas. Dutos rígidos são importantes componentes utilizados na indústria offshore, comumente empregados como flowlines e risers. Durante a vida em serviço destes componentes, eles sofrem tensões axiais cíclicas associadas a sua movimentação, ao processo de extração de petróleo e ao vórtice das marés. O aço inoxidável superduplex surgiu na última década como um material alternativo para ambientes quimicamente agressivos, mas quando catodicamente protegidos contra a corrosão, esses aços são vulneráveis a fragilização por hidrogênio. Este trabalho tem como objetivo, através da técnica de Ensaio Não Destrutivo de ultrassom phased array, monitorar o crescimento de defeitos internos e externos criados intencionalmente próximos à raiz e ao reforço da solda de um tubo de aço superduplex (UNS S32750) de 6´´ submetido a fadiga tração-tração e fragilização induzida por hidrogênio devido à proteção catódica. As inspeções foram realizadas periodicamente com varreduras de 30 a 75° ao longo da circunferência da solda, por um transdutor linear 1-D de 16 elementos e 5MHz acoplado a uma sapata de 36°. Os resultados obtidos foram utilizados para alimentar análises de integridade estrutural, obtenção da curva da/dN x ΔK. / Safe and efficient operation in oil and gas production units depends on the performance of your devices, components and structures. Rigid pipelines are important components in the offshore industry, common used as flowlines and risers. During a life in service of components, they suffer cyclical axial stresses associated with their movement, by the oil extraction process and tidal vortex. Super duplex stainless steel has emerged in the last decade as an alternative material for chemically aggressive environments, but when cathodically protected against corrosion, it is vulnerable to hydrogen embrittlement. This work aims to, through the ultrasonic non-destructive testing by phased array monitor the growth of internal and external defects created intentionally close to the root and reinforcement of the weld of a superduplex steel tube (UNS S32750) with diameter of 6" submitted to tensile-traction fatigue and hydrogen-induced embrittlement due to cathodic protection. The inspections were performed periodically with 30 to 75° scans along the circumference of the weld, by a linear transducer of 1-D, 16-element and 5MHz coupled to a wedge of 36°. The obtained results were used to feed structural integrity analyzes, obtaining the curve of da/dN x ΔK.

Componentes metálicos em operação podem estar sujeitos a diversas condições de operação deletérias. Visando avaliar os riscos de operação para evitar falhas, a análise de integridade estrutural é uma ferramenta amplamente aplicada e requer constante evolução. Por utilizar dados de ensaios não destrutivos, essa ferramenta requer cada vez mais precisão, para aprimorar seus resultados e reduzir ao máximo as falhas de componentes em operação. Por apresentar menor tempo de inspeção e maior probabilidade de detecção, o Phased Array surge como alternativa às técnicas convencionais de ultrassom. Dentre as técnicas de Phased Array, o Total Focusing Method (TFM) apresenta um dos resultados mais promissores, apresentando grande vantagem sobre técnicas convencionais de ultrassom e de Phased Array devido a sua melhor precisão e fácil interpretação dos resultados. Neste trabalho, o TFM foi aplicado em diversos blocos contendo descontinuidades usinadas, as quais simulam diferentes tipos de defeitos. O foco do TFM foi gerar blocos em três dimensões (3D) dos defeitos, facilitando a interpretação dos resultados, além da possibilidade da inserção desses blocos em softwares de análise de integridade estrutural, melhorando a precisão dos resultados. O TFM foi aplicado através do tratamento de dados de um sensor linear de Phased Array, com frequência de 5 MHz e com 64 elementos ativos. Nesse trabalho, foram desenvolvidas e aplicadas novas etapas no algoritmo do TFM para melhorar a precisão dos resultados, como a compensação da perda de energia e o half-skip. As etapas adicionais aplicadas ao algoritmo do TFM geraram bons resultados para entalhe e furos usinados nos blocos de aço carbono. Além dos blocos com defeitos usinados, foi realizada a inspeção de um bloco de aço inoxidável austenítico soldado. Para o bloco soldado, os resultados não foram satisfatórios, não sendo possível detectar defeitos existentes. Após a aplicação do TFM, foi simulado o deslocamento do sensor ao longo da peça, gerando diversas imagens 2D, as quais foram conectadas via isosuperfícies, gerando sólidos 3D dos defeitos presentes em cada bloco. Por fim, esses blocos foram exportados para um software CAD, apresentando excelente correspondência. / Metallic components in operation can be submitted to several harming operation conditions. Aiming to evaluate the operational risks to avoid failure, the structural integrity analysis is a widely applied tool and requires constant evolution. As it uses non-destructive testing data, this tool requires increasingly precision, to enhance its results and reduce the majority of the operating components failures. Because of the shorter inspection time and greater probability of detection, Phased Array is an alternative to conventional ultrasonic techniques. Among the techniques of Phased Array, the Total Focusing Method (TFM) presents one of the most promising results, offering great advantage over conventional ultrasonic and Phased Array techniques due to its better precision and easy interpretation of results. In this work, the TFM was applied to many blocks, which contain machined discontinuities simulating several defects. The objective of applying the TFM was to generate three-dimensional (3D) blocks, turning the interpretation of the results easier and giving the possibility to insert these blocks into a structural integrity analysis software, enhancing the results precision. The TFM algorithm was applied through treatment of data from a 5 MHz linear Phased Array sensor with 64 active elements. In this work, it were developed and applied new steps in the TFM algorithm, as energy loss compensation and half-skip interaction, to improve its precision. The additional steps applied to the TFM algorithm achieved great results for notch and holes machined in carbon steel blocks. In addition to the blocks with machined defects, a welded austenitic stainless steel block was inspected. For the welded block, the results were not satisfactory and it was not possible to detect the present defects. After the application of the TFM, the displacement of the transducer along the block was simulated, generating several 2D images, which were connected via isosurfaces, generating 3D solids corresponding to the defects present in each block. To conclude, these blocks were exported to a CAD software, presenting excellent matching.

The objective of this research was to quantify the effects of selected parameters on the accuracy of concrete cover measurements on bridge decks. This research involved three full-factorial laboratory experiments each designed to investigate one of three primary variables. These primary variables included distance to a parallel adjacent bar, distance to a reinforcement intersection, and incorrect bar size input for the cover meter. Each experiment also involved four secondary variables known to affect cover readings. These secondary variables included actual cover depth, meter brand, antenna type, and bar size. Statistical analyses were performed to determine the significance of each factor. A margin of error of 0.125 in., corresponding to the increase in diameter between successive U.S. standard rebar sizes, was established as the threshold for practical importance in the data analysis. Three primary findings resulted from the three experiments performed in this research. For the meters and antennas tested, the results of the field-of-view experiment indicated that, if the spacing is greater than approximately 4.0 in., the returned readings are within the threshold for practical importance established for this research. The results of the proximity-to-an-intersection experiment indicated that, regardless of where the measurement is taking place in relation to an intersection, the operator can be confident that the errors will be less than 0.125 in. as long as the bar in question is above the intersecting bar. The results of the wrong-bar-size experiment indicated that, if the operator of the cover meter does not know the actual rebar size in question, the measured cover will be within 0.125 in. of the actual cover depth as long as the meter input is within one bar size of the correct value. Obtaining accurate cover measurements on bridge decks is important for quality assurance, service life prediction, and rehabilitation programming.

Différents modèles sont développés de façon à constituer des outils génériques pour la simulation de méthodes de contrôle non-destructif par ondes élastiques guidées de plaques métalliques ou composites. Diverses méthodes de contrôle de ces structures existent ou sont à l’étude. La plupart font appel à des sources ultrasonores de taille finie ; toutes sont confrontées aux phénomènes de réflexion résultant de la taille finie des objets contrôlés. Les modèles développés traitent des phénomènes de diffraction associés aux sources et de réflexion sur un bord de plaques. Comme l’interprétation des signaux mesurés lors de contrôle par ondes guidées fait souvent appel à la notion de modes guidés, les modèles sont eux-mêmes modaux. Les cas de plaques isotropes (métalliques) et anisotropes (composites multicouches) sont considérés ; une approche générale suivant l’approximation de la phase stationnaire permet de traiter tous les cas d’intérêt. Pour les premiers, la validité d’une approximation de type Fraunhofer permet de traiter très efficacement les champs directs et réfléchis rayonnés par une source. Pour les derniers, une attention particulière est portée sur le traitement des caustiques. La méthode de la phase stationnaire étant difficile à généraliser, un modèle de pinceau, de nature plus géométrique, est proposé présentant un haut degré de généricité. Il met en cascade des termes de propagation en milieu isotrope ou anisotrope et d’interaction avec une frontière. L’équivalence de la méthode de la phase stationnaire au modèle de pinceau est démontrée pour le rayonnement et la réflexion dans une plaque isotrope, cas faisant l’objet d’une validation expérimentale. / Different models are developed to provide generic tools for simulating nondestructive methods relying on elastic guided waves applied to metallic or composite plates. Various inspection methods of these structures exist or are under study. Most of them make use of ultrasonic sources of finite size; all are sensitive to reflection phenomena resulting from the finite size of the monitored objects. The developed models deal with transducer diffraction effects and edge reflection. As the interpretation of signals measured in guided wave inspection often uses the concept of modes, the models themselves are explicitly modal. The case of isotropic plates (metal) and anisotropic (multilayer composites) are considered; a general approach under the stationary phase approximation allows us to consider all the cases of interest. For the first, the validity of a Fraunhofer-like approximation leads to a very efficient computation of the direct and reflected fields radiated by a source. For the second, special attention is paid to the treatment of caustics. The stationary phase approximation being difficult to generalize, a model (so-called “pencil model”) of more geometrical nature is proposed with a high degree of genericity. It chains terms of isotropic or anisotropic propagation and terms of interaction with a boundary. The equivalence of the stationary phase approximation and the pencil model is demonstrated in the case of the radiation and reflection in an isotropic plate, for which an experimental validation is proceeded.