A review of miniaturised Non-Destructive Testing technologies for in-situ inspections

Non-destructive testing (NDT) techniques have become attractive trends of product manufacturing, installation and post-maintenance in the aerospace, automotive and manufacturing industry, because of its benefits such as cost saving, easy to use and high efficiency etc. With the industrial products becoming large-scale, high integration and complication, developing the NDT miniaturisation technique for in-situ inspections is highly demanded and becoming an inevitable trend. However, in-situ inspection using NDT have been limited by a number of factors, such as the heavy weight, large size or complex structure etc. This paper aims to systematically identify and analyse the current state-of-the-art of NDT miniaturisation techniques in research and innovation, and discuss the challenge and prospect of miniaturisation of the commonly used NDT techniques

Radio frequency non-destructive testing and evaluation of defects under insulation

PhD ThesisThe use of insulation such as paint coatings has grown rapidly over the past decades. However, defects and corrosion under insulation (CUI) still present challenges for current non-destructive testing and evaluation (NDT&E) techniques. One of such challenges is the large lift-off introduced by thick insulation layer. Inaccessibility due to insulation leads corrosion and defects to be undetected, which can lead to catastrophic failure. Furthermore, lift-off effects due to the insulation layers reduce the sensitivities. The limitations of existing NDT&E techniques heighten the need for novel approaches to the characterisation of corrosion and defects under insulation. This research project is conducted in collaboration with International Paint®, and a radio frequency non-destructive evaluation for monitoring structural condition is proposed. High frequency (HF) passive RFID in conjunction with microwave NDT is proposed for monitoring and imaging under insulation. The small-size, battery-free and cost-efficient nature of RFID makes it attractive for long-term condition monitoring. To overcome the limitations of RFID-based sensing system such as effective monitoring area and lift-off tolerance, microwave NDT is proposed for the imaging of larger areas under thick insulation layers. Experimental studies are carried out in conjunction with specially designed mild steel sample sets to demonstrate the detection capabilities of the proposed systems. The contributions of this research can be summarised as follows. Corrosion detection using HF passive RFID-based sensing and microwave NDT is demonstrated in experimental feasibility studies considering variance in surface roughness, conductivity and permeability. The lift-off effects introduced by insulation layers are reduced by applying feature extraction with principal component analysis and non-negative matrix factorisation. The problem of thick insulation layers is overcome by employing a linear sweep frequency with PCA to improve the sensitivity and resolution of microwave NDT-based imaging. Finally, the merits of microwave NDT are identified for imaging defects under thick insulation in a realistic test scenario. In conclusion, HF passive RFID can be adapted for long term corrosion monitoring of steel under insulation, but sensing area and lift-off tolerance are limited. In contrast, the microwave NDT&E has shown greater potential and capability for monitoring corrosion and defects under insulation

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

The Application of Electromagnetic NDT Method to the inspection of Non- ferrous Cast Materials

Inspection of non-ferrous cast material is routinely carried out looking for casting defects inherent for the manufacturing process. The NDT methods employed are Radiography and Ultrasonics, primarily for sub-surface or internal defects and Penetrants fo r surface breaking defects. Electromagnetic techniques have not been used on cast material except maybe for conductivity determination. This limitation resulting fi7om the surface roughness normally associated with cast surfaces and the fact the other techniques mention above have been very successful in finding and evaluating the discontinuities sought. The possible application of Electromagnetic techniques on surfaces in the as-cast condition of non-ferromagnetic material came about because of specific problems experienced by industry. Two major investigations were offered namely; 1) Investigation of CNC material - CuNiCr [1.6%Cr] castings exhibiting oxide entrapment in the form of networks. 2) Investigation of NAB - Nickel Aluminium Bronze exhibiting selective phase corrosion on immersion in seawater. The detection and measurement of both oxide entrapment and phase selective corrosion was difficult and in cases impossible with conventional NDT methods employed for quality control of these material/component types. Time of Flight DiMaction Ultrasonics did give some 50% detectability of phase selective corrosion, but the method was found to be expensive and very time consuming. The metallurgical properties of the material and morphology of the defects have been studied for both Cupro Nickel Chromium and Nickel Aluminium Bronze cast alloys. An investigation was then conducted to study the effects of eddy current signals and their potential in detecting, both linear and cluster type defects which were predominantly interdendritic with some reported as intergranular in nature. For inspecting Cupro Nickel Chromium castings two successful eddy current methods have been developed. Detection of surface flaws was achieved by high frequency [2MHzj examination and subsurface flaws by using low frequencies [1--'IKHz] but using specifically developed sensors that provided good penetration but maintained sensitivity to the fine defects. In the case of Nickel Aluminium Bronze material, the investigation was to look at electromagnetic techniques, which best utilizes the inherent feature of permeability/conductivity associated with this non- ferromagnetic material and any changes that phase selective corrosion may produce. Some meaningful results were obtained using a combination of edd'y current excitation with detection via magneto -re s istive sensors. Testing through 30-40mm of material to detect small magnetic variation produced by only 1-2 mm of corrosion penetration was difficult to quantify. Detection and assessment however appeared hopeful when examination was carried out from the corroded surface. With quantifiable samples a meaningful technique using eddy current excitation and magneto-resistive sensor for detection can be developed