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

Magnetic Flux Leakage techniques for detecting corrosion of pipes

Oil and gas pipelines are subjected to corrosion due to harsh environmental conditions as in refinery and thermal power plants. Interesting problems such as internal and external corrosion, emerging from the increasing demand for pipeline protection have prompted this study. Thus, early detection of faults in pipes is essential to avoid disastrous outcomes. The research work presented in this thesis comprises investigations into the use of magnetic flux leakage (MFL) testing for pipe in extreme (underwater and high temperature) conditions. The design of a coil sensor (ferrite core with coil) with a magnetic circuit is carried out for high temperature conditions. The sensor thus developed lays the ground for non-destructive evaluation (NDE) of flaws in pipes through the MFL technique. The research focusses on the detection and characterization of MFL distribution caused by the loss of metal in ferromagnetic steel pipes. Experimental verifications are initially conducted with deeply rusted pipe samples of varying thicknesses in air. AlNiCo magnets are used along with Giant Magneto Resistance (GMR) sensor (AA002-02). The experiment is further repeated for saltwater conditions in relation to varying electrical conductivity with radio frequency identification (RFID) technique. A further study carried out in the research is the correlation between magnetic and underwater data communication. The study has resulted in the development and experimental evaluation of a coil sensor with its magnetic response at room and high temperatures. This makes the system effective under high temperature conditions where corrosion metal loss needs to be determined

Magnetic Flux Leakage techniques for detecting corrosion of pipes

Oil and gas pipelines are subjected to corrosion due to harsh environmental conditions as in refinery and thermal power plants. Interesting problems such as internal and external corrosion, emerging from the increasing demand for pipeline protection have prompted this study. Thus, early detection of faults in pipes is essential to avoid disastrous outcomes. The research work presented in this thesis comprises investigations into the use of magnetic flux leakage (MFL) testing for pipe in extreme (underwater and high temperature) conditions. The design of a coil sensor (ferrite core with coil) with a magnetic circuit is carried out for high temperature conditions. The sensor thus developed lays the ground for non-destructive evaluation (NDE) of flaws in pipes through the MFL technique. The research focusses on the detection and characterization of MFL distribution caused by the loss of metal in ferromagnetic steel pipes. Experimental verifications are initially conducted with deeply rusted pipe samples of varying thicknesses in air. AlNiCo magnets are used along with Giant Magneto Resistance (GMR) sensor (AA002-02). The experiment is further repeated for saltwater conditions in relation to varying electrical conductivity with radio frequency identification (RFID) technique. A further study carried out in the research is the correlation between magnetic and underwater data communication. The study has resulted in the development and experimental evaluation of a coil sensor with its magnetic response at room and high temperatures. This makes the system effective under high temperature conditions where corrosion metal loss needs to be determined

Pulsed magnetic flux leakage techniques for crack detection and characterisation

Magnetic flux leakage (MFL) techniques have been widely used for non-intrusively inspecting steel installations by applying magnetization. In the situations where defects may take place on the near and far surfaces of the structure under inspection, current {MFL} techniques are unable to determine their approximate size. Consequently, an extra transducer may have to be included to provide the extra information required. This paper presents a new approach termed as pulsed magnetic flux leakage (PMFL) for crack detection and characterisation. The probe design and method are introduced. The signal features in time�frequency domains are investigated through theoretical simulations and experiments. The results show that the technique can potentially provide additional information about the defects. Lastly, potential applications are suggested

Magnetic Leakage Internal Detection Device and Series-Parallel Detection Method for Small Diameter Ferromagnetic Spiral Heat Exchanger Tubes

Based on the calculation of magnetic circuit of the detection probe, this article designs a kind of magnetic leakage detection device and series-parallel detection method of small diameter spiral heat exchange tube to realize the safety detection of small diameter spiral heat exchange tube. The detection device includes a detection probe and a probe drive mechanism, which drives the detection probe to move in the spiral heat exchange tube. The detection probe includes an intermediate connector, a magnetizer which is arranged coaxially at both ends of the intermediate connector in turn, a steel ball support body and an end connector. The designed detection probes are mixed in series and parallel, and multiple detection probes are put together in series to be placed in a spiral heat exchange tube to form a group of detection probes in series. Then, multiple groups of detection probes in series are placed in each spiral heat exchange pipe, forming a series-parallel combination, which can detect multiple spiral heat exchange pipes at the same time and improve the detection efficiency greatly