A Novel High Sensitivity Sensor for Remote Field Eddy Current Non-Destructive Testing Based on Orthogonal Magnetic Field

Remote field eddy current is an effective non-destructive testing method for ferromagnetic tubular structures. In view of conventional sensors’ disadvantages such as low signal-to-noise ratio and poor sensitivity to axial cracks, a novel high sensitivity sensor based on orthogonal magnetic field excitation is proposed. Firstly, through a three-dimensional finite element simulation, the remote field effect under orthogonal magnetic field excitation is determined, and an appropriate configuration which can generate an orthogonal magnetic field for a tubular structure is developed. Secondly, optimized selection of key parameters such as frequency, exciting currents and shielding modes is analyzed in detail, and different types of pick-up coils, including a new self-differential mode pick-up coil, are designed and analyzed. Lastly, the proposed sensor is verified experimentally by various types of defects manufactured on a section of a ferromagnetic tube. Experimental results show that the proposed novel sensor can largely improve the sensitivity of defect detection, especially for axial crack whose depth is less than 40% wall thickness, which are very difficult to detect and identify by conventional sensors. Another noteworthy advantage of the proposed sensor is that it has almost equal sensitivity to various types of defects, when a self-differential mode pick-up coil is adopted

Ein Beitrag zur Entwicklung eines portablen Systems zur bewegungsinduzierten Wirbelstromprüfung

Die zerstörungsfreie Prüfung ist von besonderer Bedeutung im Lebenszyklus technischer Produkte. Insbesondere bei sicherheitsrelevanten Komponenten in Flugzeugen, Zügen, Pipelines oder Kraftwerken helfen Verfahren der zerstörungsfreien Prüfung, Qualitätsmängel bereits während des Herstellungsprozesses oder in regelmäßigen Wartungskontrollen zu erkennen, ohne deren Funktion zu beeinträchtigen. Heute erfordern steigende Qualitäts- und Sicherheitsanforderungen sowie die Entwicklung neuer Materialien für moderne Leichtbaukonstruktionen immer zuverlässigere Prüfverfahren, um den ordnungsgemäßen Betrieb von Bauteilen und technischen Anlagen zu gewährleisten. Für die Untersuchung von Bauteilen aus metallischen Werkstoffen kommen häufig Wirbelstromprüfverfahren zum Einsatz. Im Gegensatz zu klassischen Induktionsverfahren werden die Wirbelströme bei der bewegungsinduzierten Wirbelstromprüfung durch die Relativbewegung zwischen einer Magnetfeldquelle und einem elektrisch leitfähigen Prüfkörper hervorgerufen. Die dabei auftretenden physikalischen Effekte ermöglichen die Detektion von Fehlern im Prüfkörper. Gegenstand dieser Arbeit ist die Entwicklung eines Prinzips für ein portables System zur bewegungsinduzierten Wirbelstromprüfung, welches für den Einsatz als handgeführtes Prüfgerät zur Untersuchung von Bauteilen an ihrem Einsatzort geeignet ist. Nach einer Einführung in die zerstörungsfreie Prüfung und die in der Industrie am häufigsten eingesetzten Prüfverfahren, werden die bekannten Verfahren der bewegungsinduzierten Wirbelstromprüfung vorgestellt. Basierend auf den Erkenntnissen vorangegangener Studien im Bereich der bewegungsinduzierten Wirbelstromprüfung, erfolgt die Präzisierung der Anforderungen an das zu entwickelnde Sensorsystem und die Diskussion möglicher Lösungsvarianten. Im Rahmen dieser Ideenfindung werden zwei favorisierte Lösungsvarianten beschrieben, für die jeweils ein Messsystem zur experimentellen Validierung entwickelt und aufgebaut wird. Außerdem werden die angewendeten Verfahren der Messdatenauswertung erläutert. Das für den Anwendungszweck besser geeignete Prinzip wird anhand eines Variantenvergleichs ermittelt. Weiterführende Experimente mit dem ausgewählten Sensorsystem dienen dazu, Handlungsempfehlungen für dessen Einsatz als handgeführtes Prüfgerät abzuleiten. Darüber hinaus werden verschiedene Möglichkeiten zur Darstellung und Interpretation von Prüfergebnissen aufgezeigt.Non-destructive testing is of crucial importance in the product life cycle of technical products. Especially in the case of safety-relevant components in aircraft, trains, pipelines or power plants, non-destructive testing methods help to detect quality defects already during the manufacturing process or in regular maintenance checks without impairing their function. Today, increasing quality and safety requirements as well as the development of new materials for modern lightweight constructions require ever more reliable test procedures in order to guarantee the proper operation of components and technical systems. Eddy current testing methods are used to inspect components made of metallic materials. In contrast to classical induction methods, eddy currents in motion-induced eddy current testing are caused by the relative motion between a magnetic field source and an electrically conductive specimen. The resulting physical effects enable the detection of defects in the specimen. The subject of this work is the development of a principle for a portable system for motion-induced eddy current testing, which is suitable for use as a hand-held testing device to inspect components at their place of use. After an introduction to non-destructive testing and the testing methods most frequently used in industry, the known methods of motion-induced eddy current testing are presented. Based on the findings of previous studies in the field of motion-induced eddy current testing, the requirements for the sensor system to be developed will be specified and possible solution variants discussed. In the context of this brainstorming, two favoured solution variants are described, for each a measuring system for experimental validation is developed and set up. In addition, the applied methods of measurement data evaluation are explained. The principle most suitable for the application purpose will be determined based on a comparison of variants. Further experiments with the selected sensor system serve to derive recommendations for its use as a hand-held test device. In addition, various possibilities for the presentation and interpretation of test results are shown

Investigation of wireless power transfer-based eddy current non-destructive testing and evaluation

PhD ThesisEddy current testing (ECT) is a non-contact inspection widely used as non-destructive testing and evaluation (NDT&E) of pipeline and rail lines due to its high sensitivity to surface and subsurface defects, cheap operating cost, tolerance to harsh environments, and capability of a customisable probe for complex geometric surfaces. However, the remote field of transmitter-receiver (Tx-Rx) ECT depends on the Tx-Rx coils gap, orientation, and lift-off distance, despite each coil responding to the effect of sample parameters according to its liftoff distance. They bring challenges to accurate defect detection and characterisation by weakening the ECT probe’s transfer response, affecting sensitivity to the defect, distorting the amplitude of the extracted features, and responding with fewer feature points at non-efficient energy transfer. Therefore, this study proposed a magnetically-coupled resonant wireless power transfer (WPT)-based ECT (WPTECT) concept to build the relationship between Tx-Rx coil at maximum energy transfer response, including shifting and splitting (resonance) frequency behaviour. The proposed WPTECT system was investigated in three different studies viz., (1) investigated the multiple resonance point features for detection and characterisation of slots on two different aluminium samples using a series-series (SS) topology of WPTECT; (2) mapped and scanned pipeline with a natural dent defect using a flexible printed coil (FPC) array probe based on the parallel-parallel (PP) topology of WPTECT; and (3) evaluated five different WPTECT topologies for optimal response and extracted features and characterised entire parameters of inclined angular Rolling Contact Fatigue (RCF) cracks in a rail-line material via an optimised topology. Multiple feature extraction, selection, and fusion were evaluated for the defect profile and compared in the study, unattainable by other ECT methods. The first study's contribution investigated multiple resonances and principal component analysis (PCA) features of the transfer response from scanning (eight) slots on two aluminium samples. The results have shown the potential of the multiple features for slot depth and width characterisation and demonstrated that the eddy-current density is highest at two points proportionate to the slot width. The second study's contribution provided a larger area scanning capability in a single probe amenable to complex geometrical structures like curvature surfaces. Among the extracted individual and fused features for defect reconstruction, the multi-layer feed-forward Deep learning-based multiple feature fusion has better 3D defect reconstruction, whilst the second resonances feature provided better local information than the first one for investigating pipeline dent area. The third study's contribution optimised WPTECT topology for multiple feature points capability and its optimal features extraction at the desired lift-off conditions. The PP and combined PP and SS (PS-PS) WPTECT topologies responded with multiple resonances compared to the other three topologies, with single resonance, under the same experimental situation. However, the extracted features from PS-PS topology provided the lowest sensitivity to lift-off distances and reconstructed depth, width, and inclined angle of RCF cracks with a maximum correlation, R2 -value of 96.4%, 93.1%, and 79.1%, respectively, and root-mean-square-error of 0.05mm, 0.08mm, and 6.60 , respectively. The demonstrated magnetically-coupled resonant WPTECT Tx-Rx probe characterised defects in oil and gas pipelines and rail lines through multiple features for multiple parameters information. Further work can investigate the phase of the transfer response as expected to offer robust features for material characterisation. The WPTECT system can be miniaturised using WPT IC chips as portable systems to characterise multiple layers parameters. It can further evaluate the thickness and gap between two concentric conductive tubes; pressure tube encircled by calandria tube in nuclear reactor fuel channels.PTDF Nigeri