Eddy Current Method Research Articles

Eddy Current Identification Methods and Applications in the Chemical Industry: A Mini-Review.

As one of the most common fluid patterns in the fluid flow process of chemical production, a vortex has been successfully demonstrated to be a structure that promotes interphase mixing and enhances heat and mass transfer. Therefore, it is essential to reveal the vortex evolution laws in order to realize more efficient and less energy-consuming chemical production. In this Mini-Review, the vortex identification criteria are introduced in detail and categorized according to their development history. The application of vortex identification technology and its application in the chemical industry are explored with a large number of examples. This review enhances our understanding of vortex structures and provides plenty of innovative ideas for the study of chemical industry production.

Research of Ni—Al metal films using various physical methods

Ni—Al films obtained by resistive thermal evaporation using a "ВУП-5" vacuum station are studied. The main stages of film synthesis are established. The speed of propagation of the synthesis wave front and the radial speed of the islands are determined. Surface grain analysis and Fourier analysis are performed, providing information on the structural properties of the surface. The electrical conductivity of the thin metal film under study is determined. Keywords:Ni—Al thin metal film, resistive method, film synthesis, microstructure, coalescence, island structure, eddy current method

Application of the eddy current method for flaw detection of conductive tracks of printed circuit boards

The article discusses the creation and testing of a hardware-software complex aimed at examining the conductive paths on printed circuit boards. The complex includes a tiny eddy current transducer and a measuring system specifically designed to work with the transducer. The proposed system, which combines software and hardware components, allows for the examination of small sections of metal objects. It enables the monitoring of electrical conductivity and the determination of conductivity distribution across the object’s surface and depth. The article provides detailed explanations of the key features of the measuring system and presents the experimental findings obtained by testing different printed circuit boards. These boards were examined under various conditions, including defect-free ones and those intentionally modified to simulate defects. Dependences between the eddy current transducer signal and the different conductive tracks were established, elucidating the relationship between the transducer’s response and the properties of the tracks.

Eddy current analysis for predicting deterioration stages in alumina former radiant coils

The alumina former radiant coil is typically used as a high-temperature material. It is inevitable that the material undergoes deterioration after prolonged use. This deterioration is primarily caused by damage from the service environment and initiates carburization, resulting in a loss of its mechanical properties. Currently, the damage to the materials is only discovered when they are already broken and a precise non-destructive testing method to determine the extent of material deterioration before the damage occurs has not successfully been developed. Therefore, this research aims to study and analyze the deterioration and the causes of damage to alumina former radiant coil materials. Additionally, the study was conducted to establish a relationship between the extent of deterioration and the impedance phase angle using the eddy current test method. The experimental analysis included both as-received and in-service materials of alumina former radiant coil, which consisted of 45 % nickel by weight, 30 % chromium by weight and 4 % alumina by weight. The additional testing methods included microstructure and elemental analysis, deterioration distance measurement and impedance phase angle measurement. The results indicated that the deterioration was primarily caused by damage to the oxidation layer, facilitating the diffusion of carbon and initiating a carburization reaction on the surface of the coil. These factors unavoidably reduced the corrosion resistance of alumina former radiant coil materials. Furthermore, the reduction in chromium content as materials entered the deterioration stage led to increased hardness in the carburization zone and reduced hardness in the oxidation zone. This deterioration caused the material to exhibit ferromagnetic behavior. It was observed that as the area of deterioration increased, the size of the ferromagnetic regions also increased. Resulting in, the eddy current testing results show a variation in the impedance phase angle. Therefore, the relationship can be concluded that the impedance phase angle increases in the counterclockwise direction, corresponding to a greater extent of deterioration. The benefit of this paper is to forecast the level of the severity of deterioration quantitatively when using eddy current testing.

STUDY OF THE RELATIONSHIP BETWEEN FATIGUE CHARACTERISTICS AND ELASTIC MODULUS OF METASTABLE AUSTENITIC STEELS

This work is devoted to studying the influence of cyclic deformation on the elastic moduli of metastable austenitic steel. The estimated calculation of the modules of the strain-induced martensite and the modules of the matrix of the material (austenite) in the Voigt approximation. The modulus calculations were made according to the ultrasonic wave velocity measurements taking into account changes in the density of the material due to the difference in the volumes of the unit cells of the matrix and the ??-martensite. The volume fraction of ??-martensite and its change during cyclic deformation were determined by the eddy-current method. The influence of the strain cycle amplitude on the increase in the volume fraction of martensite was studied. The dependences of the relative change in Young's modulus, shear modulus, volume compression modulus on the number of loading cycles for metastable steel 12Kh18N10T are given. Relationships between the moduli change and the characteristics of cyclic loading of steel are obtained: the hardening of the material and the energy density in the cycle, used to calculate the service life using the methods of deformable solid mechanics. Studies shown that the critical change in the modules corresponding to the appearance of a microcrack depends on the strain cycle amplitude.The maximum change in the modules of metastable steel 12Kh18N10T was 4.5%; that by an order more than in steels that don't undergo phase transformations. A high degree of correlation between the change in elastic moduli and the fatigue characteristics of metastable austenitic steel is revealed: the hardening of the material and the energy density in the cycle. Correlations between the fatigue life of 12Kh18N10T steel and the change in elastic modulus – shear modulus and Young's modulus are obtained, which makes it possible to assess the state of the studied steel based on acoustic measurements.

MODERN PRACTICE OF USING NON-DESTRUCTIVE TESTING METHODS IN TIRE PRODUCTION

Improving the competitiveness of Russian tires requires improving the organization of the quality control system in production. The purpose of the article is to analyze the current state of the application of tire quality control methods in production. A common way to diagnose tires in the Russian industry is random control by road tests and bench tests, leading to the destruction of the product. At the same time, non-destructive testing is widely used in the global tire industry. Tire structural strength, material homogeneity, stiffness and geometric characteristics of tires are checked on test benches, which are the result of defects that can be diagnosed in a “non-invasive” way, i.e. non-destructive testing methods. Visual-optical, eddy current, ultrasonic and radiation methods of non-destructive testing are the most optimal for diagnosing continuity and obtaining the physical and mechanical characteristics of rubber and cord. Continuous flaw detection control of tires allows for the lowest cost diagnostics of hidden defects and timely improvement of the technological process. The interferometric method of non-destructive testing can be considered as an intelligent predictive diagnostics of hidden defects, bubbles, delamination, foreign inclusions in tires with nanometer accuracy. Patents and practical developments of Russian inventors in the field of interferometry testify to the high potential of mass production of domestic flaw detectors for their use in tire factories.

Thickness Measurement of Titanium-Alloy Sheets Based on the Resistance-Frequency Eddy Current Method

Thickness Measurement of Titanium-Alloy Sheets Based on the Resistance-Frequency Eddy Current Method

Application of the support vector machines method for metal analyse by an eddy current system

AbstractThe eddy current method of control analyzed and the possibility of its use for the identification of metals and alloys substantiated. It is shown that this can be done by modernizing the eddy current radio engineering system with dynamic scanning of metal samples, which consists in the use of modern microcontrollers with high‐precision ADC operation. The structural of the modernized system is presented, some aspects of processing the received response signal are considered, which made it possible to highlight the information coefficients that would represent the metal or alloy as a generalized image. It is proposed to use machine learning methods to compare an unknown sample of a metal or alloy under study with those available in the collected database, which is shown on the example of the support vector machine method, which allows for real‐time identification of metals and alloys, to carry out express control, without human intervention in the identification process.

EDDY CURRENT METHOD FOR STUDYING INHOMOGENEITIES AND DEFECTS IN THIN METAL FILMS

The variety of structure and specific properties associated with the small thickness of thin metal films lead to the fact that their physical characteristics differ significantly from the characteristics of the same materials in the bulk state. To determine the characteristics of thin metal films, the development of new non-destructive research methods is relevant. The article substantiates the advantages of the eddy current testing method for studying the surface of thin metal films of various metals. The design of a subminiature eddy current transducer designed to study the electrical conductivity, thickness and degree of damage of thin metal films is presented, and a hardware and software complex is designed that allows the control of the developed transducer. The study of metal films made it possible to show the inhomogeneity of the distribution of the substance over the surface of the substrate. The dependence of the signal amplitude of the developed transducer on the film thicknesswas also determined. To verify the results obtained, studies of the light transmittance of the films were carried out using the photometric method. Comparison of the measurement results obtained by the two methods showed a high degree of agreement betweenthe two developed methods for studying films.

Classification and Sizing of Surface Defects in Pipelines Based on the Results of Combined Diagnostics by Ultrasonic, Eddy Current, and Visual Inspection Methods of Nondestructive Testing

Classification and Sizing of Surface Defects in Pipelines Based on the Results of Combined Diagnostics by Ultrasonic, Eddy Current, and Visual Inspection Methods of Nondestructive Testing

Metal Thickness Measurement System Based on a Double-Coil Eddy-Current Method With Characteristic Ratio Detection

Eddy-current sensor systems have been employed to determine the real-time thickness distribution of metal films and the thickness at endpoint detection in metal chemical mechanical polishing (CMP) processes, to achieve global planarization and avoid over-polishing or under-polishing. However, the large lift-off distance of 3.5 mm between the sensor coil and metal film gradually decreases with continuous wear of the polishing pad, which has a strong negative impact on the sensitivity and accuracy of the thickness measurement. In this study a double-coil eddy-current sensor system, with novel characteristic ratio detection capability, is proposed for metal film thickness measurement and compared with a traditional amplitude-based method. The linear relationship between the characteristic ratio and metal film thickness that is immune to lift-off distance is demonstrated both theoretically and experimentally. The experimental results show that the proposed method performs better than the amplitude-based method, reducing the effect of lift-off distance variation and obtaining an excellent linear measurement range from 24 to 2095 nm. The measurement accuracy is as high as 2.1 nm with an excitation frequency of 1.39 MHz and a large lift-off distance of 3.5 mm. The relative measurement error is less than 1.2% and the endpoint thickness ranges from 100 to 180 nm in the Cu-CMP process, when the lift-off distance varies from 3.6 to 3.3 mm.

Detection of quenching cracks in 100Cr6 bearing steel by the eddy current method


 The article describes the research results in the identification and location of hardening cracks in 100Cr6 bearing steel using a proprietary control and measurement device for non-destructive testing using the eddy current method, Wirotest M2, and the automatic AutoWir-S1 station. A contact head with a frequency of 861 kHz was used for testing. The system recorded changes in voltage amplitude and resonance frequency. A clear decrease in the values of both parameters indicated the presence of discontinuities. The edge effect caused an increase in the voltage amplitude and a decrease in frequency, but these changes did not affect the detection of cracks. The smallest crack detected had a maximum width of approximately 20 µm and was invisible to the naked eye. The obtained surface charts clearly illustrate the course and location of individual discontinuities.

High precision thickness evaluation of thermal barrier coating with high frequency eddy current testing method

Consisting of a top ceramic coating (TC) and a bond coating (BC) layer, thermal barrier coating (TBC) is a key component of the heavy duty gas turbine blade to protect the substrate material from high working temperature. Thinning of the top coating and the thermally grown oxide (TGO) layer formed between TC and BC cause TBC thickness reduction, and may significantly affect the in-service performance of TBC. High frequency eddy current testing (HF ECT) is considered as an efficient technique for nondestructive evaluation (NDE) of the TBC thickness, but its measurement accuracy is not satisfied up to now. Aiming to realize a high precision TBC thickness evaluation with HF ECT signals, a numerical method for simulating HF ECT of TBC was developed and implemented with consideration of the dielectric properties of TC and TGO material. Through numerical simulations with the developed code, an ECT probe of optimized configuration and robust against lift-off variation was designed and fabricated for the TBC thickness evaluation. A HF ECT measurement system is then setup to investigate the validity of the prototype ECT probe and sizing method experimentally. It was found that the thickness of the TC layer can be evaluated within 10 μm accuracy for the plate TBC specimens, which reveals the HF ECT method and new ECT probe are efficient for NDE of the TBC thickness.

Distinguishing evaluation of plastic deformation and fatigue damage using pulsed eddy current testing

The vessels and pipes of nuclear power structures are subjected to complex forces. The structures suffer sudden loads that lead to plastic deformation and cyclic loads that result in fatigue damage. In practice, two types of microscopic damage may occur simultaneously. The effect of plastic deformation on material fatigue properties remains unclear, and there is a lack of effective methods to distinguish plastic deformation and fatigue damage. To address these issues, the fatigue life curve of 304 stainless steel is experimentally measured, and the influence of fatigue life due to the presence of plastic deformation under a certain load is investigated. It's identified that preset plastic deformation below 15% will increase the fatigue life of the structure. Additionally, a pulsed eddy current signal processing and reconstruction method based on the empirical modal decomposition (EBD) method is proposed. Finally, the pulsed eddy current signal characteristics of plastic deformation and fatigue damage are analyzed, and a distinguishing evaluation method of fatigue damage with preset plastic deformation is established.

Method to minimize the radial displacement dependency of an eddy-current based cross-sectional area measurement of hot-rolled rod and wire

The cross-sectional area of hot-rolled rod and wire must be measured to meet tight tolerances and high requirements of customers. An eddy-current based method utilizes a pass-through coil as a sensor element. It can measure the cross-sectional area by using the almost linear relationship between the coil reactance and the cross-sectional area of the rolled material. The lateral movement of the rod inside the coil causes deviations in the measured cross-section which must be minimized. This work outlines a successful approach for measuring the rod position within the coil using two differential pickup coils and minimizing the deviation using a simple algorithm.

Surface Profile Reconstruction of Complex Cracks Using the Signals of Rotating Eddy Current Testing Through the Eddy Current Imaging Method

In industry, natural cracks usually exist in complex forms such as adjacent, colony, irregular and crossing. Mere magnetic field is inadequate to accurately evaluate the complex cracks using eddy current testing. In this study, an improved eddy current imaging method using the signal of rotating eddy current testing was proposed to reconstruct the surface profile of complex cracks. A transformation method was adopted to transform the signals of rotating eddy current testing into those under uniform eddy current testing at the desired orientation. The deconvolution of the transformed signals and square current dipole was carried out to obtain eddy current images at eight orientations around complex cracks. By accumulating the eddy current images, the surface profile of the complex cracks was reconstructed. Simulations and experiments were carried out to illustrate, validate, and test the proposed method. The results indicated that the obtained surface profiles were clearer than those obtained by previous method using uniform eddy current testing. The improved method was effective for artificial complex slits and irregular stress corrosion crack colonies. Moreover, its performance was stable for the cracks with different angles and depths.

Electromagnetic testing of multi‐strand stay cables: novel technique and instrumentation

AbstractSteel stay cables are widely applied in various civil constructions. In recent decades, the so‐called multi‐strand stay cables have become widely used, particularly in the construction of cable‐stayed bridges. Conventional method of stay‐cable diagnostics utilizes magnetic rope testing instruments. However, because of the large diameter of multi‐strand stay cables, the appropriate magnetic instrument should have an inappropriate high mass and create a significant force of attraction between the magnetic head and the stay cable, which likely would cause damage to the cable's outer protective shell. Alternatively, the eddy current method can be used for testing of stay cables. The special probe was developed that provides equal sensitivity to surface and subsurface breaks of the strands and reduces a disturbance of irregularity of magnetic properties along the cable. On the basis of this probe, a specific electromagnetic instrument was designed for nondestructive testing of multi‐strand stay cables. The instrument was tested on a multi‐strand mock‐up and applied for inspection of the stay cables of bridges. Results of this are discussed in the article.

Ambient temperature impact on the parameters of the electrical circuit of sensing element in cluster eddy current sensor of metal chips in the lubrication systems of gas turbine engines

The detection of the wear particles in the engines lubrication systems is one of the most effective ways to assess the state of the bearing assemblies of machines and mechanisms. The most promising existing systems for online monitoring of wear particles are based on the eddy current methods for monitored parameters conversion. The reason is that such systems have the ability not only to determine the particle size, but also to recognize its magnetic properties, which makes it possible (under certain conditions) to localize the place of the defect development. At the same time, it is known that the ambient temperature changes in the monitored zone are one of the main external factors that have a significant impact on the informative parameters of eddy current converters. This is of particular importance for debris monitoring systems in high-power plants lubrication systems (e.g. gas turbine engine), where the oil temperature can vary widely (-50...+160 C). The temperature impact on the parameters of the electrical circuit of sensing element in the cluster single-coil eddy current sensor of metal chips, which is a part of the debris continuous monitoring system prototype for high-thrust aviation gas turbine engine, is studied in the article. A typical design of the single-coil sensing element is considered. The study results of the temperature effect on the sensing element inductance, as well as on the parameters of the current lead that connects the sensing element to the matching transformer and to the measuring circuit are presented. Methods for reducing the impact of temperature changes in the monitored area on the parameters of the electrical circuit of the sensing element are proposed, too.

Capabilities of eddy current ndt of soldered current-carrying joints in submersible electrical equipment

The paper shows the possibility to test the quality of soldering of small current-carrying non-ferromagnetic joints in submersible electrical equipment for oil and gas systems by the amplitude eddy current method using a highly sensitive primary transducer with a U-shaped core. The sensitivity of soldering quality testing under different conditions of generating an exciting signal is compared. It has been found that the sensitivity of NDT in the case of current amplitude stabilized in the excitation coil (current generator) is significantly higher than that in case of voltage amplitude stabilized in it (voltage generator). Possible errors in determining the level of soldering of the joints due to the variation of their cross section within the limits of tolerance according to the technology of their manufacture have been detected. Circuit solutions and software have been developed to test the level of soldering of such joins. Approbation of soldering quality testing was carried out on products manufactured under production conditions.

Analysis of formation processes of informative features in eddy current probes with pulsed excitation mode

The modern pulsed eddy current (EC) technique for flaw detection in structure inspections of aircraft and automotive elements, or other responsible constructions is typically carried out in aperiodic mode. At the same time, the unstable characteristic points of the EC signal usually used as informative parameters can restrict the potential of this excitation mode due to influence measurement errors. The article considers an application of the pulsed EC method of NDT based on the oscillatory mode. To obtain the conditions concerned with different modes of EC probe response oscillations, an equivalent scheme of the “testing object – EC probe” system was developed. The conditions represent the signal formation process and allow analyzing it for impedance and differential probes. The obtained mathematical model of the probe signals allowed for the dependence of proposed signal parameters on the characteristics of the testing object to be evaluated due to simulation. According to this, the frequency and attenuation coefficient of natural oscillations are proposed as the informative parameters. Also, the simulation results are used for developing enhanced algorithmic software for determining and analyzing the EC signals. The proposed informative parameters are experimentally investigated using a set of specimens. The obtained experimental and simulation results are correlated and it confirms the possibility of the proposed methodology to enhance the inspection procedures related to the specimen’s parameters measurements as well as the detected defect sizing.