Eddy Current Testing Technique Research Articles

An Online Monitoring Method for High- Temperature Environments Combining Eddy Current Testing and Electromagnetic Acoustic Transducer Techniques

An Online Monitoring Method for High- Temperature Environments Combining Eddy Current Testing and Electromagnetic Acoustic Transducer Techniques

Modelling the Influence of the Tube Support Plate on the Eddy Current Testing of the Steam Generator: Numerical Tools and Experimental Validation

Eddy current testing (ECT) of Steam Generator (SG) tubes is part of the maintenance program of Nuclear Power Plants. Tube Support Plates (TSP) are usually only considered as extraneous signals for tube inspection. However, for long-term operation of SGs, there is a safety concern related to the build-up of deposits in the TSPs flow holes. The clogging-up of the TSPs flow holes affect the safe thermal-hydraulic operation of SGs. The deposits come from the feedwater train and are mostly iron oxides (magnetite) with a weak electrical conductivity and magnetic permeability. The ability of ECT probes to detect and characterize TSPs deposits is therefore of great interest. The most common and industrial ECT technique, the bobbin coil, averages the surrounding electromagnetic field over 360°, whereas the geometry of tri-foiled and quadri-foiled TSPs, and thus of clogging, is rather complex and non-axisymmetric, hence motivating the evaluation of the performance of conventional ECT rotating probes used for SGs tubes inspection. Although simulation is a powerful tool to support such a study, it requires dedicated models to be made available to NDT experts, and CEA develops ECT physical models in CIVA for this purpose. In addition to standard fast CIVA modules based on 3D semi-analytical or 2D numerical calculations restricted to canonical or axisymmetric parts, respectively, CEA develops a module dedicated to the simulation of SG tube inspection based on a 3D numerical simulation. This module allows tube deformation such as ovalization, bending or tube expansion. It also allows the addition of external objects such as anti-vibration bars, different geometries of tube support plates and now their clogging by deposits. This model is used to study various influent parameters and to perform benchmarks in the framework of a scientific collaboration between the CEA and the IRSN, related for example to the inspection of the U-bend tubes or of a friction wear under the anti-vibration bars. Here, the specificity of the TSPs and their clogging justifies further investigations between CEA and IRSN to qualify the simulation model before evaluating the influence of material and geometry properties of the deposit as well as the performance of the inspection techniques. We present the main characteristics of the simulation module in CIVA.

Model-based cylinder radius and permeability estimation using eddy current testing

The material quality of metallic cylinders including microstructure is reflected in their physical properties. Eddy current testing techniques play an important role in the measurement of metallic cylinder measurement. In this paper, a cylinder radius and permeability estimation method is proposed based on the combined analytical and optimisation method. The Dodd and Deeds analytical model has been first simplified, which suggests an approximate linear relationship between the cylinder radius, permeability and coil inductance. Based on the proposed relation, the pre-estimated radius and permeability are used as the initial guess for the modified Newton–Raphson algorithm to solve the least squares problem between the measured and calculated coil inductance spectra. This method avoids the local minimum issue that occurs otherwise, to some extent. The effectiveness of the proposed method has been evaluated by numerical simulations and experiments, which indicates that fast estimation can be achieved with high accuracy.

Detection of crack on a mild steel plate by using a magnetic probe incorporating an array of fluxgate sensors

Magnetic flux leakage (MFL) and eddy current testing (ECT) are two of the most commonly used techniques to detect cracks in ferromagnetic materials. The MFL technique excels in determining the locality of a crack, while the ECT technique can provide useful information regarding the dimension and orientation of cracks. The objective of this research is to propose a simultaneous application of both MFL and ECT techniques in a single probe and to improve the visual resolution of the defect by superimposing signals from a sensor array. A magnetic probe was developed with an array of fluxgate sensors and two excitation coils. Line scan measurements and 2D mapping of artificial slits with different depths were conducted on a mild steel SS400 plate with a thickness of 12 mm to evaluate the performance of the developed probe. The line scan measurement results demonstrated the ability of the probe to detect the presence of artificial slits on the sample and to predict the depth of the slits, especially at the 110-Hz excitation frequency. Then, from the 2D mapping results, the location of the slit was determined. Furthermore, by obtaining a superimposed 2D map generated by each sensor, an improved 2D map resolution with lower background noise was obtained.

A hybrid nondestructive testing method of pulsed eddy current testing and electromagnetic acoustic transducer techniques based on wavelet analysis

It is found that the electromagnetic acoustic testing (EMAT) signal itself contains part of the pulsed eddy current testing (PECT) signal. Therefore, if the pulsed eddy current signal embedded in the electromagnetic ultrasound signal can be effectively extracted and used, the hybrid nondestructive testing method of electromagnetic ultrasound and pulsed eddy current can be truly realized. Based on the above concept, the authors have obtained some preliminary results through simple signal processing try, and which gave us a promising hope of this hybrid method. To further verify the validity and strengthen the usability of the hybrid method, more effective signal separation and extraction way to the hybrid detection signals is expected, which is the core step. In this study, a new signal separation and extraction method is proposed for the hybrid detection signals in the PECT/EMAT nondestructive testing method based on wavelet analysis strategy. The effectiveness and merits of the proposed signal separation method compared to the previous way is verified through the numerical simulation as well as experiment.

A Novel Method for Distinguishing Discontinuities In Ferromagnetic Materials Based On Eddy Current Testing Under Magnetization

Detecting inner- and outer-surface discontinuities of drill pipe is of great significance to the evaluation of the quality of the drill pipe. This paper proposes a method based on a magnetized eddy current testing technique to detect inner- and outer-surface discontinuities by analyzing the difference of the imaginary part signal characteristics of the receiving coil. For eddy current testing, the outer-surface discontinuities cause the local conductivity to be zero, while inner-surface discontinuities cause the perturbation of the magnetic permeability on the material surface. In this paper, the effects of conductivity distortion and permeability perturbation on induced eddy currents are analyzed by simulation. The conductivity distortion increases the magnetic field above the discontinuity compared to the magnetic field without the discontinuity, while the permeability perturbation reduces the magnetic field. Next, the difference in coil impedance can be used to distinguish the inner- and outer-surface discontinuities. Finally, the feasibility of the method is verified by experiments, and the results show that the inner- and outer-surface discontinuities can be discriminated.

Estimation of Thickness and Radius of Hollow Metallic Spheres With a Simplified Forward Model

The measurement of metallic spherical objects in various industrial applications has a significant role in guaranteeing safety and product quality, which can be realized by the eddy-current testing technique without contact. In this study, for the measurement of thickness and radius of non-magnetic spherical shells, the original analytical model is simplified according to the asymptotic forms of the modified spherical Bessel functions. The simplified model contains only elementary functions, and can therefore accelerates the sphere property estimation by employing the optimization approach based on the Newton-Raphson method. In numerical simulation and experimental study, the proposed method can provide accurate spherical shell radii with less computational time compared with the original analytical model.

Investigation of Microstructure and Magnetic Properties of HP40-Nb Reformer Tubes

In this paper, the results of nondestructive evaluation, structure characteristics, and magnetic properties of HP-Nb steam reformer tubes of a direct reduction unit are presented. An eddy current testing technique based on a special normal probe was performed to estimate the service life of the outer surface of the reformer tubes at a frequency of 60 kHz. The magnetic properties were investigated by vibrating sample magnetometer testing. Microstructural transformations of reference samples were performed by an optical microscope equipped with image analysis software and scanning electron microscopes. With exposure to severe operational conditions in oxidizing atmospheres and high temperature, microstructural changes such as oxidation and transformation of M23C6 and M7C3 carbide in the carburization zone, and chromium depletion in the austenite matrix, can be intensified. The tubes were inspected on a point basis and the eddy current data were presented as an impedance map. The results of the eddy current testing and vibrating sample magnetometer showed that microstructural changes due to operational conditions affect the electromagnetic response of the tubes.

Eddy Current Testing Methods and Design for Pipeline Inspection System: A Review

Non-destructive testing and complex systems integration are commonly used in transportation, aircraft, automotive, manufacturing, petrochemical, and defence. Eddy current testing (ECT) is a common non-destructive evaluation technique, especially in the coating, nuclear, and oil and gas industries. However, the eddy current testing method must continue to focus on the probe’s construction and application. It ascribed noisy data to inadequate detection and a severe false alarm problem. Nonetheless, only few academics have elaborated on the intelligent ECT crack detection method. This study provides an overview of the eddy current testing technique and the probe structure design elements that influence fracture detection accuracy. The first section describes the Eddy current testing by encircling coil system for a differential probe (ECDP) and an encircling coil for an absolute probe design (ECDP). The explanations focus mostly on the probe’s creation and detection in Rotating electromagnetic field eddy current (RoFEC). The advantages and disadvantages of eddy current testing surrounding probes are analysed. In addition, a summary of prior studies investigating testing samples of ferromagnetic pipe, steel rod, and wire rope is presented. The second segment focuses on Eddy current testing employing a Giant Magnetoresistance (GMR) sensor system, with a particular emphasis on sensor arrays, GMR, and conventional eddy current coils for crack identification. Finally, a comprehensive overview of eddy current testing methods and design for non-destructive pipeline inspection systems is presented.

Lift-Off Effect Evaluation by Using Eddy Current Testing Technique on Copper (C101)

This study aims to develop an eddy current testing (ECT) probe that generates eddy current signals when a coil is placed above copper101 metal testing with and without nonconductive coating and the presence of lift-off height, i.e., 0, 2.5, 5.0, 7.5, and 10.0 0.5 mm. Then, the metal test with a variety of thicknesses, i.e., 1.5, 3.0, and 5.0 0.5 mm, and with varies of surface defects, i.e., 10, 20, and 30  0.5 mm, engraved on the metal testing. The coil probe is a rodshaped solenoid coil designed with an iron core with 65 mm length, 5 mm area, and 200 N turns. It demonstrates how the rod-shaped solenoid coil may be used to detect various surface defects on copper101 (C101). The optimal frequencies for C101 are 7.850 MHz. In conclusion, the output voltage signals for larger surface defect sizes increase but decrease as the thickness becomes thicker. Furthermore, as the lift-off height increases, the output voltage for both coated and non-coated metal decreases accordingly. Therefore, besides comparing the output voltage for coated and non-coated metals, there are minor differences which shows that the ECT technique in this studyis capableto detect surface defects appropriately.

Fast Estimation of Metallic Pipe Properties Using Simplified Analytical Solution in Eddy-Current Testing

The eddy-current testing technique has been extensively explored for the measurement of metallic pipes in various industrial processes. In this study, a simplified analytical model of metallic pipes encircled by a coaxial sensor is derived according to the asymptotic forms of modified Bessel functions. The original Dodd and Deeds (DD) model is thus approximated by an elementary function describing the relationship between the measured inductance spectrum and the pipe properties. Due to the simple nature of the elementary function, the Jacobian matrix can be evaluated much more efficiently. Accordingly, a fast Newton–Raphson method-based optimization approach is developed. The proposed method has been evaluated by comparing it with the numerical simulation of the finite-element method (FEM) and experimental measurements which indicate its effectiveness for the measurement of metallic pipe properties.

An Eddy-Current Testing Method for Measuring the Thickness of Metallic Plates

Thickness measurements of metallic plates are mandatory in many industrial scenarios. Methods based on Eddy Current Testing (ECT) are ideal for fast and accurate online contact–less thickness measurements, making them very attractive in the Industry 4.0 scenario. This contribution is focused on a specific and robust ECT technique proposed in the past by the scientific community. The main limitation is its applicability to thin materials only, where the thickness of the material is much smaller than the overall size of the ECT probe. Extending the range of applicability to thicker materials, introduces a progressive and severe degradation of the measurement accuracy. In this paper, we analyse the theoretical foundation of this method with an entirely original approach based on the celebrated Buckingham’s π theorem. In doing this, we draw the complete theoretical picture of the method, providing a simple, clear and rigorous view of its performance and intrinsic limitations. Moreover, we propose two solutions, one analytical and the other iterative, to accurately estimate the thickness of materials from thin to thick values. Finally, a numerical analysis combined with an experimental campaign confirms the effectiveness of the proposed solutions making the method suitable for industrial and other applications.

Locating and Imaging Fiber Breaks in CFRP Using Guided Wave Tomography and Eddy Current Testing.

In this paper, guided Lamb wave tomography and eddy current testing (ECT) techniques were combined to locate and evaluate fiber breaks in carbon-fiber-reinforced plastic (CFRP) structures. Guided wave testing (GWT) and computed tomography (CT) imaging were employed to quickly locate fiber breaks in the CFRP plate. From B-scans performed along two different fiber orientations (0 and 90 degrees), parallel-beam projections of different features were extracted from the guided wave signals, using signal-processing techniques (such as wavelet and Hilbert transforms) and statistical functions (such as skewness and kurtosis). The parallel-beam projections of each individual feature were used as input in computed tomography imaging reconstruction to approximately estimate the location of fiber breaks. From the obtained reconstructed images, image-fusion techniques were applied to get complementary information from multiple source images into one single image. After locating the fiber breaks, C-scans were performed in the vicinity of the damage, using an ECT probe with double excitation configuration to evaluate the condition of the fiber break.

Preparation of solenoid probe for Eddy Current Testing technique probe

The most crucial components in the system of eddy currents are the sensitivity of the probe to deliver a signal to detect a defect on the material efficiently. When the turns are closely spaced and the length is substantially more than the radius of the turns, the solenoid is perfect. This paper presents a development of a solenoid probe for the eddy current testing (ECT) technique probe to detect defects. The objectives of this research are to design and construct a high sensitivity rod-shaped solenoid probe, to find the optimal frequency for each metal testing (i.e., Copper (Cu), Aluminium (Al), and Stainless Steel) for this solenoid probe, and to obtain the output testing signals defects with vary of thickness (i.e., 1.5 mm, 3.0mm, and 5.0 mm). In addition, a hole of an artificial defect (i.e., 7.0 mm, 14.0 mm, 21.0 mm) has been drilled on each of the metal testings. This rod-shaped solenoid coil was designed with an iron core with 65 mm length, 5 mm area, and 200 turns. It demonstrates how the rod-shaped solenoid coil may be used to detect various flaws in copper (Cu), aluminium (Al), and stainless steel. The optimal frequencies for copper were 7.850 MHz, Aluminium was 7.383 MHz, and Stainless-Steel metal was 7.956 MHz.

Simple Giant Magnetoresistance Probe Based Eddy Current System of Defect Characterization for Non-Destructive Testing

The purpose of this paper is to present a new giant magnetoresistance (GMR) sensor, in eddy current testing technique for surface defect detection, in conducting materials, we show that the GMR based eddy currents probe is more sensitive than the inductive probe. A flat coil mounted on ferrite pot used to produce an alternate magnetic field, which gives rise to eddy currents in the material under test. Aluminum plates use with defects have nominal depths, widths, and lengths. The defects scanned with the sensing axis perpendicular to the defect length. Two parameters extracted from the GMR output voltage signal obtained, and a simple correlation between the defect’s dimensions and the GMR output voltage proposed.

A self-frequency-conversion eddy current testing method

Eddy current testing (ECT) technology is currently one of the effective methods for non-destructive testing of aviation materials. In the application of ECT technology, a lower operating frequency is generally used for aviation metal materials, while carbon fiber reinforced plastics (CFRP) often require higher operating frequencies due to the low conductivity characteristic. However, multiple materials are often used simultaneously in aircraft manufacturing, including metallic materials and CFRP. Therefore, due to the difference in materials, the traditional ECT technology needs to be carried out in the ultra-large frequency range (1 kHz to 100 MHz) during the ECT inspection process of the aircraft, which will bring great difficulties to instrument development and actual operation. Concerning this issue, a self-frequency-conversion ECT method is proposed in this paper, and the corresponding ECT system was developed. The proposed method has two detection signals simultaneously, the current signal and the frequency signal, which are used to characterize the defects of CFRP and metal materials, respectively. Experimental studies on CFRP and aluminum alloys were carried out using the proposed method. The experimental results show that the proposed method can realize the defect detection of metal materials and CFRP in the conventional frequency range of 1 kHz to 1 MHz. Compared with the traditional ECT technique, the proposed method greatly reduces the operating frequency range and can provide better detection sensitivity, which is an ECT technology with great engineering application value.

Burst eddy current testing with diamond magnetometry

In this work, a burst eddy current testing technique based on the employment of a diamond nitrogen vacancy (NV) center magnetometer with the Hahn echo (HE) sequence is demonstrated. With the confocal experiment apparatus, the HE-based NV magnetometer attains a magnetic sensitivity of 4.3 nT/Hz and a volume-normalized sensitivity of 3.6 pT/Hz mm−3, which are ∼five times better than the already existing method under the same conditions. Based on the proposed magnetometer configuration, a burst eddy current testing prototype achieves a minimum detectable sample smaller than 300 μm and a spatial resolution of 470 μm, which is employed to image different metallic specimens and detect layered internal structures. Since this prototype comprises remarkable high sensitivity, it exhibits various potential applications in the fields of security screening and quality control. Moreover, its biocompatibility and promising nanoscale resolution pave the way for electromagnetic testing in the fields of biomaterials.

Simulation of eddy current testing of steam generator tubes with wear and secondary side magnetite deposits

The steam generator (SG) tubes of pressurised water reactors are prone to degradation and are periodically inspected using eddy current testing (ECT) techniques. SGs provide a safety barrier between the radioactive primary side and the non-radioactive secondary side. Historically, a major degradation issue was stress corrosion cracking of tubes made of alloy 600. In modern SGs, better resistance to stress corrosion cracking is observed with the replacement of alloy 600 by alloy 690. However, this alloy does not prevent tubes from wear at support locations or wear resulting from fretting with loose parts. Long-term operation of SGs also leads to non-volatile species accumulation in the secondary side of the SGs, mainly magnetite. Magnetite deposits may build up as a dense and solid material on top of the tubesheet (hard sludge) and also in the flow slots of tube support plates, therefore modifying the general flow pattern and velocity of the secondary fluid. This has detrimental effects on the safe operation of SGs. The clogging-up ratio of the flow slots therefore needs to be assessed. The development of an ECT simulation model to address tube wear and magnetite deposits in SGs is presented. This model is based on the CIVA NDT platform. A bobbin coil signal is simulated and its performance for tube wear and magnetite deposit evaluation is discussed.

Detection of Outer Wall Defects on Steel Pipe Using an Encircling Rotating Electromagnetic Field Eddy Current (RoFEC) Technique

In recent years, the rotating electromagnetic field eddy current (RoFEC) testing technique has attracted widespread attention due to its various advantages for inspecting tubular structures. However, most of the related work was focused on detecting inner wall defects on metal pipes using feed-through probes, which are often not applicable for outer wall defect detection. This work pushes forward the encircling RoFEC technique and demonstrates its feasibility for detecting outer wall defects. First, the basic principle of the encircling RoFEC technique is introduced. A three-dimensional finite element (FE) model was built in COMSOL to analyse the distribution of the rotating electromagnetic field and study the interaction between the defects and eddy currents. The axial component of the resultant magnetic field due to defects was selected as a characteristic signal and obtained from the FE models to study the factors, including pipe tilt, defect circumferential location, defect orientation and defect size, that influence the detection performance. An encircling RoFEC system using a probe with six excitation windings and a single bobbin pickup coil was constructed and used to inspect a steel pipe with one axial and one circumferential defect. The obtained voltage signal due to defects can form a Lissajous pattern in the impedance plane and be used for defect evaluation. The results showed that the encircling RoFEC technique can detect outer wall defects of both orientations and determine the circumferential location of the defect.

Investigation of Rotating Eddy Current Testing Simulation Using Simplified Model

To reduce the time of simulation for rotating Eddy current testing (RECT) technique, a simplified model without modeling probe was proposed previously. However, the applicability of the simplified simulation model was unknown. In this paper, the applicability of the simplified model for the RECT technique was investigated. The application condition of the simplified model was provided by comparing it with the results of the traditional simulation model. The simplified model was suitable for the study of cracks shorter than 70% size of the uniform Eddy current induced by the probe in a traditional model or experiment. The experiment was conducted to validate the simplified model. Moreover, using the simplified model, the effects of crack depth, orientation, and exciting frequency were studied. The deeper the crack depth was, the greater peak value of [Formula: see text] signal was. The crack angle was linear with the phase of signal. The exciting frequency affected the amplitude and phase of the signal at the same time.