Magnetic sensors and gradiometers for detection of objects

Disertační práce popisuje vývoj nových detekčních zařízení s anizotropními magnetorezistoryThis thesis describes development of innovative sensor systems based on anisotropi

Накладные вихретоковые преобразователи: системы возбуждения оптимального электромагнитного поля (обзор)

Development of technical tools with improved metrological and operational characteristics is the actual problem of the eddy current testing. Ensuring the optimal distribution of the electromagnetic excitation field in the testing zone carries out confident detection of the defects and determination of their geometrical parameters by means of eddy current testing. The purpose of the work was to conduct an analysis of scientific and technical information in the field of eddy current testing to study of the use of electromagnetic excitation fields with a priori specified properties, as well as to generalize and systematize the accumulated experience and approaches to conduct theoretical research in this direction.A review of publications in the field of non-destructive electromagnetic testing devoted to the improvement of the excitation systems of eddy current flaw probes was carried out. The authors considered approaches in which a uniform distribution of the electromagnetic field on the control object surface was achieved by linear and non-linear optimal synthesis of excitation systems, provided the immobility of the probe relative to the testing object. Analysis of eddy current probe designs with a homogeneous excitation field created by circular, rectangular tangential and normal coils, as well as by creating a rotational excitation field was carried out. The authors studied designs of the excitation coils of probes with fields of complex configuration characterized by the original fractal geometry which can increase the probability of identifying defects that were not amenable to detection by classical probes.Studies that suggested the formation of optimal configuration fields in a given area using magnetic cores, field concentrators made of conductive materials and specially shaped screens were analyzed. The authors studied approaches to the implementation of the optimal synthesis of excitation systems of probes with uniform sensitivity in the testing zone using surrogate optimization for cases of moving testing objects taking into account the speed effect.The experience, as well as the results of theoretical studies devoted to the problem of designing eddy current probes with uniform sensitivity in the testing zone due to the uniform density distribution of the induced currents flowing in the object were generalized and systematized. As a result, the classification of probes on a number of features that characterize the excitation systems was proposed.Актуальной задачей вихретокового контроля является разработка технических средств с улучшенными метрологическими и эксплуатационными характеристиками. Уверенное обнаружение дефектов и определение их геометрических параметров средствами вихретокового контроля осуществляется при обеспечении оптимального распределения электромагнитного поля возбуждения в зоне контроля. Цель работы заключалась в проведении анализа научно-технической информации в области вихретокового контроля для изучения сведений об использовании электромагнитных полей возбуждения с априори заданными свойствами, а также обобщения, систематизации накопленного опыта и подходов к проведению теоретических исследований в данном направлении.Проведён обзор публикаций в области неразрушающего электромагнитного контроля, посвящённых совершенствованию систем возбуждения преобразователей вихретоковых дефектоскопов. Рассмотрены подходы, в которых однородное распределение электромагнитного поля на поверхности объекта контроля достигается линейным и нелинейным оптимальным синтезом систем возбуждения при условии неподвижности преобразователя относительно объекта контроля. Проведён анализ конструкций вихретоковых преобразователей с однородным полем возбуждения, созданным круговыми, прямоугольными тангенциальными и нормальными катушками, а также за счёт создания вращательного поля возбуждения. Изучались конструкции катушек возбуждения преобразователей с полями сложной конфигурации, характеризующиеся оригинальной фрактальной геометрией, которые позволяют увеличить вероятность выявления дефектов, не поддающихся обнаружению классическими преобразователями.Также проанализированы исследования, в которых предлагается формирование полей оптимальной конфигурации в заданной зоне с применением магнитопроводов, концентраторов поля из проводящих материалов и экранов специальной формы. Изучались подходы к реализации оптимального синтеза систем возбуждения преобразователей с равномерной чувствительностью в зоне контроля с использованием суррогатной оптимизации для случаев движущихся объектов контроля с учётом эффекта скорости. Обобщён и систематизирован опыт, а также результаты теоретических исследований, посвящён-ных проблеме проектирования вихретоковых преобразователей с равномерной чувствительностью в зоне контроля, обусловленной однородным распределением плотности индуцированных токов, протекающих в объекте. Предложена классификация преобразователей по ряду признаков, характеризующих их системы возбуждения

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

Challenges in improving the performance of eddy current testing: Review

Eddy current testing plays an important role in numerous industries, particularly in material coating, nuclear and oil and gas. However, the eddy current testing technique still needs to focus on the details of probe structure and its application. This paper presents an overview of eddy current testing technique and the probe structure design factors that affect the accuracy of crack detection. The first part focuses on the development of different types of eddy current testing probes and their advantages and disadvantages. A review of previous studies that examined testing samples, eddy current testing probe structures and a review of factors contributing to eddy current signals is also presented. The second part mainly comprised an in-depth discussion of the lift-off effect with particular consideration of ensuring that defects are correctly measured, and the eddy current testing probes are optimized. Finally, a comprehensive review of previous studies on the application of intelligent eddy current testing crack detection in non destructive eddy current testing is presented

Non-Destructive Techniques Based on Eddy Current Testing

Non-destructive techniques are used widely in the metal industry in order to control the quality of materials. Eddy current testing is one of the most extensively used non-destructive techniques for inspecting electrically conductive materials at very high speeds that does not require any contact between the test piece and the sensor. This paper includes an overview of the fundamentals and main variables of eddy current testing. It also describes the state-of-the-art sensors and modern techniques such as multi-frequency and pulsed systems. Recent advances in complex models towards solving crack-sensor interaction, developments in instrumentation due to advances in electronic devices, and the evolution of data processing suggest that eddy current testing systems will be increasingly used in the future