Eddy Current Nondestructive Testing Research Articles

Quantitative Nondestructive Evaluation of Cold Spray Manufactured Aluminum Alloy 6061 and Copper Samples

Cold spray (CS) is a solid-state process for depositing thick layers of material via the successive high-velocity impact of powder particles onto a solid surface, which leads to high rates of deformation, interparticle bonding, and coating build-up. Although CS is finding commercial utilization in non-load-bearing repair and coating applications, clear nondestructive characterization procedures are necessary to realize its potential in load-bearing structural applications. In this study, the viability of electrical conductivity and through thickness ultrasound wave velocity measurement methods was studied to serve as a means for nondestructive quantitative measurement for quality control in CS and potentially other additive manufacturing (AM) methods. Eddy current, ultrasound, porosity, hardness, and uniaxial tensile strength tests were conducted on CS deposited layers of aluminum alloy 6061 and copper on aluminum alloy 6061 and commercially pure copper substrates, respectively. CS gas dynamic parameters were intentionally and systematically varied to result in corresponding discrete differences in mechanical properties of deposits. Ultrasound measurements of longitudinal wave velocity and eddy current electrical conductivity measurements showed good correlation with process conditions, microstructural characterization results, and destructive mechanical tests (hardness, tensile). The results of this work show that ultrasound wave velocity and electrical conductivity correlate well with increased particle impact velocity in CS deposited aluminum and copper blocks, which evidently show an incremental decrease in porosity, increase in hardness, and increase in tensile strength. The outlined ultrasound and eddy current nondestructive testing methods present effective means for quantitative assessment of cold spray deposited structures while intact with the substrate.

Model of an E-cored probe over layered conductor containing corrosion for eddy current testing

PurposeIn eddy current nondestructive testing, ferrite-cored probes are usually used to detect and locate defects such as cracks and corrosion in conductive materials. However, the generic analytical model for evaluating corrosion in layered conductor using ferrite-cored probe has not yet been developed. The purpose of this paper is to propose and verify the analytical model of an E-cored probe for evaluating corrosion in layered conductive materials.Design/methodology/approachA cylindrical coordinate system is adopted and the solution domain is truncated in the radial direction. The magnetic vector potential of each region excited by a filamentary coil is derived first, and then the expansion coefficients of the solution are obtained by matching the boundary and interface conditions between the regions and the subregions. Finally the closed-form expression of the impedance of the multi-turn coil is derived by using the truncated region eigenfunction expansion (TREE) method, and the impedance calculation is carried out in Mathematica. In the frequency range of 100 Hz to 10 kHz, the impedance changes of the E-cored coil and air-cored coil due to the layered conductor containing corrosion are calculated, respectively, and the influences of corrosion on the coil impedance change are investigated.FindingsAn analytical model for the detection and evaluating of corrosion in layered conductive materials using E-cored probe is proposed. The model can quickly and accurately calculate the impedance change of E-cored coil due to corrosion in layered conductor. The correctness of the analytical model is verified by finite element method and experiments.Originality/valueAn accurate theoretical model of E-cored probe for evaluating corrosion of multilayer conductor is presented. The analytical model can be used to detect the inhomogeneity of layered conductor, design ferrite-cored probe or directly evaluate the corrosion defects of layered conductors.

APPLICATION OF THE RED PITAYA PLATFORM IN THE TECHNOLOGY OF PROTOTYPING AUTOMATED EDDY CURRENT TESTING SYSTEMS

Automated eddy current non-destructive testing has an important role in the quality inspection system for products made of conductive materials both at the production stage and during their operation. The appearance of novel alloys, the complexity of product geometry and inspection conditions, and the increased requirements for the reliability and accuracy of inspection results stimulate the acceleration process of creating new eddy current inspection tools. The technology of prototyping makes it possible to solve this problem. The purpose of the article is to review the functionality and technical characteristics of Red Pitaya for use in the technology of prototyping eddy current inspection, as well as to create a prototype architecture of an automated eddy current inspection system based on it.The choice of the Red Pitaya platform as a convenient tool for prototyping automated systems was made due to its functionality, reliability, and availability. In general, the article highlights the advantages and prospects of using the Red Pitaya platform in the prototyping of automated eddy current non-destructive testing systems. The aspects of the Red Pitaya hardware and its capabilities for expanding the functionality, which allows to create highly efficient and flexible control systems, are considered in detail. The compatibility of Red Pitaya with other devices and accessories is considered, which significantly increases its versatility and adaptability to various requirements and applications.The article highlights the importance of using the Jupyter Notebook application in combination with Red Pitaya as a convenient tool for software development. This helps to facilitate the process of creating and programmatically implementing complex signal processing algorithms in eddy current control systems, and provides flexibility in creating new software products.Modern trends and prospects for the development of eddy current testing, market needs, and the ability to adapt to different application scenarios are taken into account in the proposed architecture of the prototype automated eddy current testing system.

Automated Eddy Current System for Aircraft Structure Inspection

Abstract Aircraft part diagnostics are crucial during both production and maintenance, with eddy current nondestructive testing (ECNDT) being the method of choice due to its cost-effectiveness, informativeness, productivity, and reliability. ECNDT excels regardless of surface condition or coatings. It’s employed for diagnosing various aircraft components, necessitating diverse transducer types, excitation modes, and advanced signal processing. To improve ECNDT, this article explores integrating harmonic and impulse excitation modes in a single tool to enhance informativeness. Building upon a wireless eddy current system, the authors propose a comprehensive method for processing and displaying information suitable for object condition monitoring systems. The system includes automated transducer mode control and experimental data processing algorithms. The constant expansion of tested objects and new materials underscores the need to enhance the theoretical foundations of eddy current non-destructive testing, refine signal processing techniques, and identify informative signs. This demands the development of new automated ECNDT tools, and this article offers a promising avenue for improvement. The results include model and experimental tests of system components, showcasing the potential of this approach to enhance ECNDT effectiveness, automation, and informativeness in the realm of aircraft part diagnostics.

New design of rotating eddy current probe for arbitrary orientation cracks detection

PurposeDetecting the orientation of cracks is a major challenge in the development of eddy current nondestructive testing probes. Eddy current-based techniques are limited in their ability to detect cracks that are not perpendicular to induced current flows. This study aims to investigate the application of the rotating electromagnetic field method to detect arbitrary orientation defects in conductive nonferrous parts. This method significantly improves the detection of cracks of any orientation.Design/methodology/approachA new rotating uniform eddy current (RUEC) probe is presented. Two exciting pairs consisting of similar square-shaped coils are arranged orthogonally at the same lifting point, thus avoiding further adjustment of the excitation system to generate a rotating electromagnetic field, eliminating any need for mechanical rotation and focusing this field with high density. A circular detection coil serving as a receiver is mounted in the middle of the excitation system.FindingsA simulation model of the rotating electromagnetic field system is performed to determine the rules and characteristics of the electromagnetic signal distribution in the defect area. Referring to the experimental results aimed to detect artificial cracks at arbitrary angles in underwater structures using the rotating alternating current field measurement (RACFM) system in Li et al. (2016), the model proposed in this paper is validated.Originality/valueCEDRAT FLUX 3D simulation results showed that the proposed probe can detect cracks with any orientation, maintaining the same sensitivity, which demonstrates its effectiveness. Furthermore, the proposed RUEC probe, associated with the exploitation procedure, allows us to provide a full characterization of the crack, namely, its length, depth and orientation in a one-pass scan, by analyzing the magnetic induction signal.

Technique for measuring the thickness of a non-conductive coatings on a non-magnetic electrically conductive base metals with automatic take account of the influence of the specific electrical conductivity of the base metal

The results of measurements of the thickness of a non-conductive coating on an electrically conductive non-magnetic base metal using the existing amplitude technique of eddy current non-destructive testing are strongly influenced by the specific electrical conductivity of the base metal. To eliminate this problem, it is proposed to use an eddy current probe with amplitude-phase signal processing. Its graduation is carried out using several base metals with different specific electrical conductivity using a coating thickness simulator, the number of graduation points is comparable to the resolution of the thickness gauge. To calculate the thickness of the coating, taking into account the specific electrical conductivity of the base, an algorithm is used to determine the involvement of a point in a polygon.

Modeling of Eddy Current NDT Simulations by Kriging Surrogate Model

ABSTRACT In this article, the Kriging surrogate model is proposed to accelerate the model-assisted probability of detection (MAPoD) analysis for eddy current nondestructive testing (NDT). The Kriging surrogate model is the key for enabling the efficient MAPoD analysis, considering huge number of uncertainties propagate in the eddy current NDT system, by replacing the time-consuming physical model. To generate the model responses of NDT system, a precise physical model based on the adaptive cross approximation algorithm accelerated boundary element method (BEM) is applied. In the numerical case, the MAPoD study of eddy current for detecting surface flaws in the conducting plate is analyzed. By comparing the PoD metrics achieved by the pure physical model and by the Kriging surrogate model, the accuracy and efficiency of the proposed surrogate model are demonstrated.

Inductance-to-digital converters (LDC) based integrative multi-parameter eddy current testing sensors for NDT&E

Sensors’ signal conditioning and digital interface are important for sensor technologies, digital transformation, and the Internet of Things (IoT) in particular. Frequency output sensors and inductance-to-digital converters (LDC) offer distinct advantages over Analog-to-Digital Converter (ADC) interfaces. To miniaturize the eddy current testing system and achieve multi-parameter measurements, this paper reviews eddy current signal conditioning and digital interfaces in the field of displacement sensors and non-destructive tests & evaluation (NDT&E). After review and comparison of different signal conditioning and digital interfaces, the LDC chip is used in eddy current testing for multiple parameter measurements including lift-off distance and defect detection. An LDC-based integrative eddy current non-destructive testing method is proposed. The LDC chip provides AC to drive the LC resonator composed of the sensor coil and the parallel capacitor. By measuring the resonance frequency and parallel resistance (Rp) of the LC resonator, the simultaneous measurement of the lift-off distance and the defect is achieved. Based on the method, the testing experiments of two kinds of specimens made of aluminium and steel were carried out under different lift-offs. Experimental results show that both parameters of frequency and Rp of the LC resonator can intuitively reflect the defect depth and lift-off. Frequency- Rp curves can be used to quantify defect depth and lift-off distance and differentiate the material. This work also illustrates an integrated approach of signal conditioning and digital interface for multiple parameters or feature measurement for integrated eddy current NDT&E. The work opens a new way for addressing multiple parameter measurements of eddy current NDT & E including lift-off estimation and defect characterization via digital interfaces. It has the potential to bridge the gaps in metrology of geometry, displacement measurement, and NDT&E for defect detection and material characterization.

Influence of the variety of steel tube materials on the impedance behavior of non-destructive Eddy current testing

Influence of the variety of steel tube materials on the impedance behavior of non-destructive Eddy current testing

Improving Magnetic Field Response of Eddy Current Magneto-Optical Imaging for Defect Detection in Carbon Fiber Reinforced Polymers

A large number of carbon fiber reinforced polymers have been applied to aircraft and automobiles, and many nondestructive testing methods have been studied to detect their defects. Eddy current magneto-optical imaging nondestructive testing technology has been widely used in the detection of metal materials such as aircraft skin, but it usually requires a large excitation current and, at present, can only detect metal materials with high conductivity. In order to take full advantage of the innate benefits and efficiency of eddy current magneto-optic imaging and enable it to detect defects in carbon fiber reinforced polymers with weak conductivity, it is necessary to improve the magnetic field response of the eddy current magneto-optic imaging system and explore suitable excitation and detection methods. The scanning eddy current magneto-optical imaging nondestructive testing device built in this study has improved the magnetic field response of the system, and the eddy current magneto-optical phase imaging testing method has been proposed to detect the crack defects of carbon fiber reinforced polymers. The effectiveness of the method has been verified by simulation and experiment.

Theoretical Predictions of Perturbed Magnetic Flux Density Components Due to Narrow Flaws in ECT

This work proposes a semianalytical technique based on the boundary element method (BEM) to predict the signals due to flaws (cracks) that are typically encountered in eddy current (ECT) nondestructive testing (NDT). Two case studies, for two different narrow opening notches in a finite thickness aluminium plate, were performed by experimental measurements to corroborate the theoretical model. The signal which has been modelled is the perturbation in the magnetic flux density (MFD) components <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B_x</i> , <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B_y</i> , and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B_z</i> due to narrow opening flaws. The proposed analytical model uses the magnetic vector potential (MVP), arising from electric dipole sources, to determine the voltage induced in a hypothetical small circular loop located around the evaluation point. Based on the linear relationship between the voltage induced and the magnetic flux in the surface enclosed by the hypothetical loop, a linearity constant that transforms the induced voltage to the MFD component has been computed. Appropriate vector potential Green’s functions have been used to transform the electric dipole sources to the magnetic vector potential components to determine the voltage induced in the hypothetical loop.

High frequency eddy current inspection of fibre placement in Carbon Fibre Reinforced Polymer Composites

This paper presents experimental and simulation studies of high frequency eddy current non-destructive testing (NDT) methods for inspection of carbon fibre reinforced polymer (CFRP) composites. It is well known that CFRP composite materials are widely used in industry as structural components, and products based on such materials are increasingly developed and introduced to market. In recent years, non-conventional eddy current method operating at high frequencies for NDT of composites begins to attract attention. It provides a non-contact, couplant-free option of inspection when compared with the other NDT methods currently used in industry. As eddy current relies on fibre fabrics in individual plies to form the current pathways, the eddy current paths in composite are unsurprisingly complex due to the structural features of composite laminates when compared with that in homogenous conducting metals for which conventional eddy current NDT is often used in industry. It will be noted that the knowledge is still limited so far about the eddy current distributions in composite laminates due to lack of effective theoretical and numerical models. This paper will focus on the development of a new numerical model that is suitable for use in simulations of high frequency eddy current inspection of fibre placements. An effective model is desirable for understanding the performance dependence of the eddy current testing method on the material properties, composite structural features, and other parameters involved. In this model, the fibre tow layout of individual plies is taken into consideration. The collection of the pickup signals by the sensor probe shows clear images of the fibre placement in different layers. The simulation results are compared with experimental results of fibre placement imaging. The model is useful for understanding the physical process for inspection of composites using high frequency eddy current methods, and for studying the influence of the controllable parameters involved.

Efficient Model Assisted Probability of Detection Estimations in Eddy Current NDT with ACA-SVD Based Forward Solver.

Model assisted probability of detection (MAPoD) is crucial for quantifying the inspection capability of a nondestructive testing (NDT) system which uses the coil or probe to sense the size and location of the cracks. Unfortunately, it may be computationally intensive for the simulation models. To improve the efficiency of the MAPoD, in this article, an efficient 3D eddy current nondestructive evaluation (ECNDE) forward solver is proposed to make estimations for PoD study. It is the first time that singular value decomposition (SVD) is used as the recompression technique to improve the overall performance of the adaptive cross approximation (ACA) algorithm-based boundary element method (BEM) ECNDE forward solver for implementation of PoD. Both the robustness and efficiency of the proposed solver are demonstrated and testified by comparing the predicted impedance variations of the coil with analytical, semi-analytical and experimental benchmarks. Calculation of PoD curves assisted by the proposed simulation model is performed on a finite thickness plate with a rectangular surface flaw. The features, which are the maximum impedance variations of the coil for various flaw lengths, are obtained entirely by the proposed model with selection of the liftoff distance as the uncertain parameter in a Gaussian distribution. The results show that the proposed ACA-SVD based BEM fast ECNDE forward solver is an excellent simulation model to make estimations for MAPoD study.

A Basic Study on GMR Sensor-Based Eddy Current Nondestructive Testing Method for Corrosion Detection in Concrete Structures

A Basic Study on GMR Sensor-Based Eddy Current Nondestructive Testing Method for Corrosion Detection in Concrete Structures

Tunnel-magnetoresistive-based Pulsed Eddy Current Probe for Inspection of Corrosion under Insulation

The problem of corrosion in the industrial oil and gas pipes has been one of the major contributors in catastrophic structural failures. Among the various types of corrosion, corrosion under insulation (CUI) has been known to cause serious problems. Pulsed eddy current (PEC) non-destructive testing has shown its effectiveness in detecting hidden CUI. Most PEC systems have been developed by using an inductive coil as their sensing device, while some use a magnetic sensor which potentially offers better resolution. A new probe design based on a solid-state Tunnel magnetoresistance (TMR) is presented. TMR sensors offer higher sensitivities compared to other commercially available sensors. The performance of the probe is evaluated by using ferromagnetic mild steel plates that have thicknesses in the range of 8mm to 12mm at different stand-offs with a thin aluminium sheet under the probe. The different thicknesses represent different corrosion levels, while the stand-offs and thin aluminium sheet are to mimic the insulation of different thicknesses and the cladding in the real pipeline structure. The results show an overall mean absolute error (MAE) of 0.19 mm, which is better than our existing Hall-device-based PEC probe.

Effect of Linear Crack Size and Location Relationship to Piston Stress and Damage Tolerance

In the quantitative characterization of linear defect structure of Piston Alloy, non-destructive testing and micro-morphology of defect, shape and outline of prefabricated linear defect are used in this paper. Based on ANSYS finite element software, an experimental simulation of line defect was carried out by using the finite element software of micromechanics. The defects of piston alloy components are assigned with material parameters, the model grid is divided, the boundary condition is defined and the finite element simulation is carried out under ANSYS/Mechanical environment. The calculation of the micro-stress field of the interface with various defects is obtained. Under the service condition of high-power density diesel engine, the local stress concentration caused by line defect is less than the strength limit of alloy material. Therefore, in this location eddy current testing non-destructive testing control line defect size is 0.12 mm×0.2 mm×5 mm. It is suitable for Eddy current nondestructive testing of piston components and can ensure the material safety and work reliability of Piston components under service condition.

Assessment and detection of stress corrosion cracking by advanced eddy current array nondestructive testing and material characterization

Oil and natural gas pipelines are under a combination of loading (stresses) due to their pressurized content and some kind of corrosive environmental operational condition including the content materials as well as soil side which is called Stress Corrosion Cracking (SCC). Since the SCC occurs at stresses within the range of typical design stresses, it can cause catastrophic failures without a significant indication in pipeline integrity beforehand. Efficient Nondestructive Inspection (NDI) during the operational life of the structures can prevent such failures by providing accurate information regarding size and characteristics of the SCC flaws. Since majority of SCC defects occur in surface and near surface regions of metallic pipeline, electromagnetic NDI (Eddy Current) is proved to be a promising inspection technique. In this study, Eddy Current Array (ECA) methodology, as a recent advancement and developed version of traditional Eddy Current (EC) NDI technique, was used for assessment of SCC generated in steel samples representing steel pipeline's material in a laboratory setup. ECA as an advanced eddy current NDI uses an array of eddy current coils to provide the scanning image of the inspection area. Prefabricated notches and SCC after a period of load-corrosion application to the samples were detected and characterized. Accuracy and repeatability of the results showed the efficiency of ECA for SCC characterization.

Imaging and quantitative detection of complex defects with a flexible electromagnetic array sensor

The eddy current non-destructive testing (NDT) method has the advantages of high sensitivity and fast speed and is widely used in the inspection of key metal parts in the military and in industry. The existing scanning imaging method based on eddy current detection will cause the defect and the image to be inconsistent when the angle between the sensor and the defect is different, which will result in the inability to accurately quantify the defect based on the image. Therefore, this paper proposes a method based on a three-axis platform and a flexible eddy current array sensor to realise defect imaging and quantitative detection. First, the sensor is installed on the three-axis motion platform through a flexible substrate. It is intended that the three-axis motion platform will achieve full coverage detection of the surface of the test-piece and the overall image of the surface of the test-piece can be obtained by splicing. Then, the characteristic signal is subjected to bicubic interpolation to obtain clearer two-dimensional and three-dimensional defect images. Finally, morphological image processing is used to binarise the defect greyscale image and then the shape and size of the defect are obtained through contour pixel analysis. Experimental results show that this method can effectively overcome the impact on imaging when the sensor and the defect are at different angles and ensure the consistency of the imaging of the defect at any angle, so as to realise the imaging and quantification of any defect.

Quality reliability analysis of flash welding joint of cold-rolled 50JW800 silicon steel strip

In this study, the quality reliability of the flash butt welding (FBW) joint of a 50JW800 silicon steel strip is analyzed through metallographic observation, cupping tests, and tensile tests. It is found that the recrystallization in some areas of the joint is insufficient, as is the mechanically forced connection, owing to the plastic deformation and uneven heat distribution of the joint during the process of FBW. Insufficient recrystallization is the root cause of strip breakage during cold rolling. The quality reliability of the 50JW800 silicon steel strip FBW joint is also analyzed using eddy current nondestructive testing technology. It is found that the eddy current testing signal has a good response to different structural characteristics of the joint. Therefore, eddy current test technology can be used to ensure the quality reliability of silicon steel strip FBW joints in actual production.

Mechanism of Magnetic Permeability Perturbation in Magnetizing-Based Eddy Current Nondestructive Testing.

DC magnetization is generally considered to suppress the usual local magnetic permeability variation and increase the penetration depth for magnetizing-based eddy current testing (MB-ECT) of ferromagnetic materials. In fact, such simple explanations lead to rough nondestructive evaluation and cause new neglected non-uniform magnetic characteristics. Hence, the “perturbation” of the internal magnetic field variation is analyzed using a magnetic dipole model and the mechanism of magnetic permeability perturbation in MB-ECT is revealed. The theoretical analysis and simulations show that a significant permeability perturbation always appears around a defect and presents opposite features with strong and weak magnetization. Furthermore, experimental results indicate that the hidden signal component arising from the local permeability perturbation is critical for both far-side surface and near-side surface defects in the MB-ECT method.