A model development for reconstruction of three-dimensional defects based on MFL signals

Corrosion has been statistically placed as the primary cause for pipeline failures well beyond other factors. The inability to accurately size corrosion defects located in pipelines can result in erroneous integrity strategies with fatal consequences, even when appropriate inspection processes have been conducted. Underestimation or overestimation of the defect size causes on one hand pipeline failures and on the other unnecessary assessments. Several strategies for defect sizing based on MFL signals have been developed in recent years. However, the industry still urges for reliability improvements. The current thesis develops a model based on calibration curves for the reconstruction of defects, based on MFL signals. A thorough study of different parameters involved allows for the understanding of the relationships between defect dimensions and MFL signal features. The methodology of this research includes theoretical, numerical and experimental assessments resulting in the development of a reliable three-dimensional model. Calibration curves are reported for inner as well as for outer defect configuration. Such curves permit the accurate establishment of the defect length and depth by means of the signal duration and amplitude. The results of this study for a single defect can be further implemented in order to investigate the superposition of MFL signals coming from adjacent defects. The MFL signal superposition is demonstrated through simulations and experiments.Nach der Statistik ist Korrosion, neben anderen Faktoren, die primäre Ursache für Rohrleitungsversagen. Die Unfähigkeit, Korrosionsfehler in Rohrleitungen genau zu dimensionieren, kann zu fehlerhaften Integritätsstrategien mit fatalen Folgen führen, selbst wenn geeignete Prüfprozesse angewendet werden. Eine Unterschätzung oder Überschätzung der Fehlergröße führt einerseits zu Pipelineversagen und andererseits zu unnötigen Untersuchungen. In den letzten Jahren wurden verschiedene Strategien zur Fehlergrößenbestimmung basierend auf Signalen des magnetischen Streuflusses entwickelt. Die Industrie drängt jedoch weiterhin auf eine Verbesserung der Zuverlässigkeit durch diese Technik. In der vorliegenden Arbeit werden Kalibrierkurven für die Rekonstruktion von Fehlstellen basierend auf Signalen des magnetischen Streuflusses beschrieben. Eine gründliche Untersuchung der verschiedenen Einflussparameter ermöglicht die Beziehungen zwischen den Dimensionen der Fehlstellen und Signalmerkmalen des magnetischen Streuflusses zu verstehen. Die Methodik dieser Forschung umfasst theoretische, numerische und experimentelle Bewertungen, die zur Entwicklung eines zuverlässigen dreidimensionalen Modells führen. Kalibrierkurven werden sowohl für Innen- als auch für Außenfehler angegeben. Solche Kurven ermöglichen die genaue Ermittlung der Fehlstellenlänge und -tiefe anhand der Signallänge und -amplitude. Die Ergebnisse, die in dieser Studie für Einzelfehler gewonnen wurden können verwendet werden, um Untersuchungen an benachbarten Fehlstellen durchzuführen, bei denen sich die Signale des magnetischen Streuflusses überlagern

Improvements to ultrasonic imaging with post-processing of full matrix capture data

Ce mémoire présente les comparaisons entre les différentes méthodes de reconstruction "Total Focusing Method" (TFM) et des différents algorithmes modifiés qui utilisent les données obtenues avec la "Full Matrix Capture" (FMC) dans le but d'améliorer certains points clés présents dans les méthodes d'imageries, tel que les problèmes de reconstructions en sous-résolution ou bien des améliorations sur la détection. Les algorithmes conçus sont comparés en analysant les mêmes données pour les différents cas. De ces cas, l'imagerie de défauts isolés et puis ensuite celle d'une séquence de défauts très rapprochée ont été effectuées. Différentes recherches ont été effectuées sur les performances des algorithmes de reconstruction TFM en basse résolution. Ce mémoire montre que tous les types d'algorithmes présentés, soit la TFM standard, la TFM avec enveloppe d'Hilbert, la TFM intégration, la TFM intégration avec enveloppe d'Hilbert, la TFM restreinte en angle, la Migration et la Migration d'Hilbert sont toutes des méthodes valides de post-traitements des données capables d'imager convenablement les défauts présentés. Les différentes méthodes de reconstruction démontrent également des habilitées dépassant celles de la TFM standard dans certains points clés, en ayant seulement quelques points négatifs, tel que les temps de traitement ou bien l'augmentation du bruit de l'image.This study shows the comparison between standard Total Focusing Method (TFM) and various modified algorithms using the data obtained from the Full Matrix Capture (FMC) in order to improve on some key points present in the aforementioned standard method of imaging, such as sub-resolution problems and improvements on detection. The designed algorithms were compared by processing the same data for different cases. Off those cases, the imaging of isolated defects and then imaging an array of close defects were analyzed. Further work have also been done on the performance of TFM algorithms in low resolution settings. The study has shown that all presented algorithms, which are the standard TFM, the Hilbert envelope TFM, the integration TFM, the Hilbert integration TFM, the angle restricted TFM, the Migration and the Hilbert Migration are all valid image post-processing reconstruction methods able to properly detect the defects presented. The different reconstruction methods used have also shown to outperform the standard TFM in a few key points, while having a few negative points such as the processing time and the increase noise

Advances in Potential Drop Techniques for Non-Destructive Testing

In the field of Non-Destructive Testing, Potential Drop (PD) techniques have been used for decades, especially in the petrochemical and power generation industries, for monitoring crack growth and wall thickness variations due to corrosion and/or erosion in pipes, pressure vessels and other structures. Inspection is carried out by injecting currents in the specimen to be tested and measuring the arising electrical potential di erence between two or more electrodes placed on its surface. The presence of a defect generally increases the resistance and hence the measured voltage drop; inversion of these data can give information on the size and shape of the defect. However, while the principle underlying these techniques is relatively simple, some di culties have been encountered in their practical applications. Many commercial systems based on PD methods, for instance, require the injection of very large currents in order to obtain su ciently large signals; doubts have been raised on the stability of these methods to variations in the contact resistance between the electrodes and the inspected material. The present work aims to show that some of these problems can be easily overcome, and to evaluate the capabilities of PD techniques for crack sizing and corrosion mapping. After a brief review of the advantages, disadvantages and applications of the main electromagnetic methods for Non-Destructive Testing, an experimental setup for Potential Drop measurements which was developed for this work and which uses small alternating currents (AC) is described. The setup is benchmarked against existing PD systems and then used to validate a model that allows AC PD simulations to be run with a commercial Finite Element code. The results of both numerical simulations and experimental measurements are used to investigate the possibility of sizing defects of complex geometry by repeating the analysis at several di erent frequencies over a broad range, and of reconstructing the depth pro le of surfacebreaking defects without the need for assumptions on their shape. Subsequently, the accuracy to which it is possible to obtain maps of corrosion/erosion on the far surface of an inspected structure is discussed, and results obtained with an array probe that employs a novel arrangement of electrodes are presented. Finally, conclusions are drawn and suggestions for further research are made

Ultrasonic sensor platforms for non-destructive evaluation

Robotic vehicles are receiving increasing attention for use in Non-Destructive Evaluation (NDE), due to their attractiveness in terms of cost, safety and their accessibility to areas where manual inspection is not practical. A reconfigurable Lamb wave scanner, using autonomous robotic platforms is presented. The scanner is built from a fleet of wireless miniature robotic vehicles, each with a non-contact ultrasonic payload capable of generating the A0 Lamb wave mode in plate specimens. An embedded Kalman filter gives the robots a positional accuracy of 10mm. A computer simulator, to facilitate the design and assessment of the reconfigurable scanner, is also presented. Transducer behaviour has been simulated using a Linear Systems approximation (LS), with wave propagation in the structure modelled using the Local Interaction Simulation Approach (LISA). Integration of the LS and LISA approaches were validated for use in Lamb wave scanning by comparison with both analytical techniques and more computationally intensive commercial finite element/diference codes. Starting with fundamental dispersion data, the work goes on to describe the simulation of wave propagation and the subsequent interaction with artificial defects and plate boundaries. The computer simulator was used to evaluate several imaging techniques, including local inspection of the area under the robot and an extended method that emits an ultrasonic wave and listens for echos (B-Scan). These algorithms were implemented in the robotic platform and experimental results are presented. The Synthetic Aperture Focusing Technique (SAFT) was evaluated as a means of improving the fidelity of B-Scan data. It was found that a SAFT is only effective for transducers with reasonably wide beam divergence, necessitating small transducers with a width of approximately 5mm. Finally, an algorithm for robot localisation relative to plate sections was proposed and experimentally validated