Eddy Current Probe Research Articles

Effects of Mechanical Scanning Speeds on Eddy-Current Detection of Cavity Defects

This article presents a distributed current-source (DCS) model considering the perturbation of the eddy-current (EC) field and its EC-generated magnetic flux density (MFD) caused by the defect in a moving conductor. The perturbed EC field, which is formulated into two subproblems (with and without a defect) in state space, is iteratively solved for the transient responses of a 3-D EC system and used to analyze the parametric effects on the fine and coarse detection of cavity defects. The DCS model improves the computational efficiency by reducing the solution domain and the number of experiments for parameter optimization, leading to the development of an EC probe consisting of an MFD sensor and a pair of rectangular electromagnets. Experimentally evaluated on a testbed configured on a computer numerical control (CNC) lathe for 2-D area scanning, the findings demonstrate the feasibility of mechanical scanning at a high speed to improve EC detection efficiency.

Mitigation of the effect of variations in the electrical conductivity of the material via two-frequency eddy current testing of the thickness of the electrically conductive wall under significantly varying influence parameters

The paper analyzes feasibility of the two-frequency eddy current method for measuring the thickness of an electrically conductive wall under significantly varying test and influence parameters of the test object — the lift-off between the eddy current probe and the test object surface, and the electrical conductivity of the material. An analytical solution was used to determine the dependence of the two-frequency signal of the surface eddy current probe on the influence parameters of the test object. The informative parameters used to simultaneously mitigate the effect of the two influence parameters were the amplitude of the added high-frequency voltage to determine the lift-off, the phase of the added low-frequency voltage to determine the wall thickness, and the phase of the added high-frequency voltage to suppress variations in the electrical conductivity of the material. The calculated dependences of the informative parameters on the test and influence parameters were analyzed. The use of nonlinear functions of the inverse transformation of the informative parameter into the test parameter was shown to efficiently mitigate the effect of variations in the lift-off on measurement results. A method to suppress variations in the electrical conductivity of the test object material is proposed. It implies the correctionof the phase of the added low-frequency voltage by the correction value calculated from the parameters of the lift-off and wall thickness, and high-frequency phase variation caused by varying the electrical conductivity of the material.

Накладні вихрострумові перетворювачі подвійного диференціювання як ефективний засіб вирішення проблем неруйнівного контролю

Накладні вихрострумові перетворювачі подвійного диференціювання як ефективний засіб вирішення проблем неруйнівного контролю

Nondestructive evaluation by eddy current and ultrasonic technique of 475�C embrittlement effects in dss duplex stainless steels and corrosion behavior

In this paper, a non-destructive evaluation of the embrittlement effect in duplex stainless steel DSS 2205 aged from 5 h to 100 h at a temperature of 475 ° C was performed by Eddy current and ultrasonic techniques, in addition the corrosion behavior was carried out after heat treatment at 475°C. The experimental results show that an inverse behavior was observed between normalized impedance and hardness in aging time at 475°C; when the normalized impedance of the Eddy current probe was decreased, hardness was increased with aging time. The longitudinal ultrasonic velocity and transversal velocity were calculated in this study for each sample. The Young’s modulus and the Shear modulus were computed from the two velocities. The investigation carried out shows a sensitivity of Eddy current and ultrasonic technique to the microstructure changing observed at 475 ° C, due to embrittlement in duplex stainless steel. The effect of heat treatment at 475°C on the corrosion behavior was also evaluated by Eddy current on a long time and revealed the important changing in corrosion resistance due to spinodale decomposition of the ferrite phase.

Impact of Whirl and Axial Motion on Ball Bearing Turbocharger Dynamics

Ball bearing turbochargers (TCs) incorporate an angular contact ball bearing cartridge to reduce friction and oil consumption, improving the efficiency of internal combustion engines. In this investigation, axial and radial TC rotor motion was experimentally measured and used to develop a model of the TC rotor-bearing system, allowing for a detailed analysis of the TC bearing under varying operating conditions. In order to achieve the experimental objectives of this investigation, eddy-current proximity probes were used to measure the radial motion at the turbine and compressor sides of the TC. The measured radial motion shows whirl with subharmonics at low speed. The measured axial motion of the rotor was found to increase with TC speed. In order to analytically investigate the bearing dynamics, a complete TC model was developed that includes the mass distribution and flexibility of the TC compressor, shaft and turbine, and squeeze-film dampers (SFDs) that support the bearing cartridge. The model was used to replicate the whirl and axial motion of the test rig and then to determine which model parameters could be adjusted to minimize whirl without negatively affecting the bearing dynamics. Simulation results revealed that centrifugal effects cause a change in the bearing internal geometry, with a small clearance becoming a preload at higher speeds. When this effect is coupled with less compliant SFDs, the subharmonics are reduced and the overall sliding and number of large load cycles at the ball–race contacts are minimized, contributing to lower bearing friction and improved overall life.

Characteristics of Eddy Current Attenuation in Double-Layer Metallic Plate and Measurement of Gap Thickness

ABSTRACT Multilayer metallic plate is made by stacking homogeneous or heterogeneous metallic plates and connecting them with fasteners. The air-gap thickness between the adjacent layers affects the performance of the plate structure. The eddy current testing (ECT) technology has been used for the nondestructive testing of multilayer plate. However, the effect of air gap on the characteristics of eddy current (EC) attenuation in multilayer plate remains unclear and the study of the relation between the response of the EC probe and the gap thickness is very limited. The computation results of the paper show that the air gap in a double-layer plate reduces the amplitude of EC density in the bottom layer and decreases the rate of EC attenuation in the top layer. The mechanism is revealed. The effect of gap thickness on probe response is investigated. It is found that the presence of air gap makes the EC response either larger or smaller, depending on the working frequency. The reason is explained based on the characteristics of EC attenuation. Thereupon, the experiment of measuring gap thickness using the ECT is carried out.

Towards Enhanced Eddy Current Testing Array Probes Scalability for Powder Bed Fusion Layer-Wise Imaging

This work presents a new eddy current testing array probe and readout electronics that target the layer-wise quality control in powder bed fusion metal additive manufacturing. The proposed design approach brings important benefits to the sensors' number scalability, exploring alternative sensor elements and minimalist signal generation and demodulation. Small-sized, commercially available surface-mounted technology coils were evaluated as an alternative to usually employed magneto-resistive sensors, demonstrating low cost, design flexibility, and easy integration with the readout electronics. Strategies to minimize the readout electronics were proposed, considering the specific characteristics of the sensors' signals. An adjustable single phase coherent demodulation scheme is proposed as an alternative to traditional in-phase and quadrature demodulation provided that the signals under measurement showed minimal phase variations. A simplified amplification and demodulation frontend using discrete components was employed together with offset removal, vector amplification, and digitalization implemented within the microcontrollers' advanced mixed signal peripherals. An array probe with 16 sensor coils and a 5 mm pitch was materialized together with non-multiplexed digital readout electronics, allowing for a sensor frequency of up to 1.5 MHz and digitalization with 12 bits resolution, as well as a 10 kHz sampling rate.

Surface EDDY current probes of double differential type as an effective tool to solve non-destructive inspection problems

Surface EDDY current probes of double differential type as an effective tool to solve non-destructive inspection problems

Experimental study of different innovative measurement methodologies applied to a canned pulsed eddy current testing probe suitable for dilation measurement of test specimens

A compact pulsed eddy current testing probe is being developed for the online dilation measurement of test specimens, examined in the high-temperature environment of material testing reactors. The probe has to be canned with metallic clad to protect it from the corrosive sodium-potassium coolant medium present in the material testing reactor. Electromagnetic modelling of the probe was carried out to compute the distribution of time-dependent eddy current density in the vicinity of the probe. It is understood that the slope of the pulsed eddy current signals in the specific time zone where the lift-off point of intersection occurs show a good correlation to the distance between the face of the probe and the test specimen. This paper discusses the experimental study of employing different measurement methodologies at room temperature with the canned pulsed eddy current probe to evaluate its feasibility for dilation measurement. It is observed that a phenomenon of a divergence of signals, akin to the lift-off point of intersection, occurs just after the transient part of the pulsed eddy current signals. Slope analysis of these diverging pulsed eddy current signals was carried out for characterisation of the probe in the air medium as well as the metallic medium present in the gap between the probe face and the test specimen.

Study on the Relationship Between Thickness Measurement and Strength Defect of Buried Pipeline

Based on the principle of electromagnetic eddy current testing, aiming at the problems of heavy workload and difficult location of defects in the periodic inspection of buried pipelines, the eddy current distribution of pipelines, probes, and defects is modeled and simulated by using ANSYS EM simulation software, the correlation model between pipeline parameters, excitation signals, and received signals is established, and the quantitative relationship between pipeline wall thickness parameters and eddy current distribution is clarified. Based on the accuracy and engineering application ability, the through pipe wall thickness detection device is optimized, and the structure of the eddy current probe is improved. The experimental results show that the improved eddy current probe can improve the detection accuracy of 6.9% in detecting the induced eddy rheology in the workpiece and effectively improve the efficiency of pipe wall thickness defect location and pipe radius detection, which can provide a new reference for the regular detection and troubleshooting of buried pipelines.

Eddy current convergence probes with self-differential and self-nulling characteristics for detecting cracks in conductive materials

Eddy current convergence probes with self-differential and self-nulling characteristics for detecting cracks in conductive materials

Differential Koch Planar Eddy Current Probe Sensitivity Boosting by Iron Particulate Sheet

Differential Koch Planar Eddy Current Probe Sensitivity Boosting by Iron Particulate Sheet

Study on the Crack Detectability Based on Koch Differential Pick-up Planar Eddy Current Probe

Study on the Crack Detectability Based on Koch Differential Pick-up Planar Eddy Current Probe

Real‐Time Strain Detection Technology for Steel Structures Based on Eddy Current Effect

To avoid strains in steel structures in special equipment caused by excessive alternating loads, which cause stress concentrations in local areas and reduce the strength and pressure‐bearing capacity of the steel structures, a method for evaluating the strain state of the steel structures using the eddy current effect is proposed, and the relevant testing device is developed. The RMS voltage and tension values were tested and fitted linearly with sampling time, and their linear correlations after fitting were 0.9978560 and 0.9967905, respectively. To investigate the method’s practical application, the effect of strain on the impedance of the eddy current probe was first studied theoretically, followed by the design and fabrication of a strain detection device comprised of an eddy current probe and a signal processing system. Finally, tensile strain experiments were carried out on 5 mm thick standard Q235 steel tensile specimens using a universal tensile machine and the linear equation of RMS voltage versus strain was obtained analytically. Theoretical and experimental tests have shown that the device can detect each strain stage and quantify the strain within the elastic stage by fitting a linear equation.

Reducing the Impact of Influence Factors on the Measurement Results from Single-Coil Eddy Current Sensors

Single-coil eddy current sensors (SCECS) form a separate and independent branch among the existing eddy current probes. Such sensors are often used for aviation and aerospace applications where the conditions accompanying the measuring process are harsh and even extreme. High temperatures (up to +600 °C in the compressor and over +1000 °C in the turbine of gas turbine engines), the complex shape surfaces of the monitored parts, the multidimensional movement of the power plants' structural elements, restrictions on the probes number and their placement in the measuring zone are the main factors affecting the reliability and accuracy of the measurement results obtained by the sensors. The article provides an overview of the relevant approaches and methods for reducing the impact of influence factors on the measurement results from SCECS based on the extensive experience of more than 30 years of research and development being carried out in the Institute for the Control of Complex Systems of Russian Academy of Sciences. The scope of the solutions discussed in the article is not limited to SCECS measurement systems only but can also be extended to the systems with primary transducers of other designs or other physical principles.

Possibility of eddy current testing of low-conductive heterogeneous media

The possibility of copper ore quality testing for proportion of minerals containing copper in it by the eddy current method has been studied. Copper ore is presented as a low-conductivity heterogeneous medium consisting of two homogeneous ore constituents (enclosing rock and copper mineral). These constituents have significantly different specific electrical conductivity (SEC). For the analysis, the effective medium approximation is used. In this case a heterogeneous ore can be considered homogeneous with an effective SEC, which depends on the quantitative composition of its constituents. To solve this problem, the surface parametric eddy current probe (ECP) of a local type has been developed. Its design is optimized for operation at high frequencies (units – tens of MHz). ECP winding consists of 10 turns with a diameter of 11 mm, which wound up in one layer on a dielectric frame. The ECP signals in the complex plane from samples of copper ore with different content of copper mineral (chalcopyrite) in the resonant operation mode are studied using eddy current flaw detector of Eddycon C type. The operating frequencies are 5, 7 and 9 MHz. It has been established that with increasing frequency in the specified range, signals amplitude has a pronounced tendency to decrease. It is shown that as the frequency increases from 5 to 7 MHz, the phase sensitivity of the developed ECP to the content of chalcopyrite in the ore also decreases. Thus, the phase angle between signals from ore samples with low and high chalcopyrite content at the frequency of 5 MHz is 110°, and at the frequency of 7 MHz – 87.5°. With a further frequency increase to 9 MHz, the phase sensitivity remains practically unchanged, and the amplitude of the signals continues to decrease. This can be explained by a decrease of the ECP sensitivity to SEC changes with a transition to the over-extreme operating point of the complex plane by operating frequency increase. The fundamental possibility of using the eddy current method for the quantitative testing of chalcopyrite in copper ore has been confirmed. Prospects for further research related to the development of an integral-type ECP, in particular, screen ones, whose signals are determined by the content of chalcopyrite in copper ore samples as a whole, are formulated.

Design and Performance Research of a New Dual-Excitation Uniform Eddy Current Probe.

A dual-excitation uniform eddy current probe, composed of two excitation coils placed tangentially and one detection coil placed horizontally, is developed to solve the difficulties of detection rate and direction recognition of crack defect. Firstly, a probe simulation model is established using COMSOL Multiphysics, and the differences of eddy current distribution between the dual-excitation probe and the traditional probe are investigated. Then, the influence of the distance between excitation coils on sensitivity and the test capability for crack defects with different depths and directions are investigated. Besides, the sensitivity of the dual-excitation probe is compared to that of the traditional probe made of the same coils. Finally, a physical probe and an experimental system are developed, and the performance of the dual-excitation probe is tested. The experimental results show that the probe developed in this paper exhibits a slightly higher sensitivity than the traditional probe for crack defects with different depths in the range of 0.5 mm-4.0 mm; the measurement accuracy of crack length is about 3.0 mm and can avoid missing detection of crack defects with different directions. In testing, the detection signal can be compensated to achieve precision measurement by identifying the angle of crack defects. This dual-excitation uniform eddy current probe can be used for precise quantification and direction identification of crack defect in eddy current testing.

A novel film eddy current probe having a detection coil interleaved to the excitation coil and the amplified effect by ferromagnetic amorphous alloys particles

This paper presents the development of a square-film eddy current (EC) probe with a detection coil interleaved to the excitation coil to detect cracks on the surface of aluminum. The probe with an interleaved design between the detection coil and the excitation coil can eliminates the distance between the test piece surface and both coils and improves the signal-to-noise ratio. Furthermore, iron-based ferromagnetic amorphous alloy particles (FAAP) without conductivity placed above the probe to increase the magnetic flux density and enhance the ECs induced on the surface of the test piece. Moreover, FAAP also increases the interlinkage magnetic flux to the detection coil. A finite element simulation was conducted for the film EC probe to confirm the advantages of FAAP. Furthermore, experiments with probes were conducted using an aluminum plate with artificial cracks. In addition, the measurement results were analyzed to confirm the enhancement of the crack-detection ability of the FAAP. • A film probe with a detection coil interleaved to the excitation coil to detect was proposed. • The amorphous magnetic alloy particles was installed above the film eddy current probe. • The amorphous magnetic alloy particles enhanced the eddy current induced on the test piece. • The signal amplitudes significantly increased by the amorphous magnetic alloy particles.

Research and application of deformation measurement method of hydraulic turbine head cover

Aiming at the deformation of hydraulic turbine head cover during operation, a non-contact eddy current sensor is proposed. In this method, the turbine pit wall is taken as the static reference point, a fixed support is erected on it, and the eddy current probe is fixed at the other end of the support. Measure the gap change between the eddy current sensor probe and the head cover to calculate the absolute deformation of the head cover. The effectiveness of the proposed method is verified by taking the lifting amount test of hydraulic turbine head cover in a power plant as an example. The results show that this method has the characteristics of simple test equipment, strong adaptability and high accuracy, and can be applied to the field test of hydraulic turbine head cover deformation.

Artificial Neural Networks for Inverse Problems in Damage Detection using Computational and Experimental Eddy Current

A new method for computing fracture mechanics parameters applicable for measuring tests relying on Eddy currents is proposed. This method is based on inversing Eddy current with simultaneous use of Artificial Neural Networks (ANN) for the localization and the shape classification of defects. It allows the reconstruction of cracks and damage in the plate profile of an inspected specimen to assess its material properties. The procedure consists on inverting all the Eddy current probe impedance measurements which are recorded according to the position of the probe, the excitation frequency or both. In the non-destructive evaluation by Eddy currents or in the case of an inverse problem which is difficult to solve, results from a lot of variety of concepts such as physics and complex mathematics are needed. The corresponding solution has a significant impact on the characterization of cracks in materials. On the other side, a simulation by a numerical approach based on the finite element method is employed to detect cracks in materials and eventually, study their propagation. It is shown here that this method has emerged as one of the most efficient techniques for prospecting cracks and enables the study of an increase in size of cracks and its propagation in aluminum material. Besides, it can easily predict future defects in different mechanical parts of a given material and be useful in the treatment of materials than the process of changing parts. It has been proven that it gives good results and high performance for different materials.