Pulsed Eddy Current Technique Research Articles

The Evaluation of Pulsed Eddy Current Technique for Detection and Characterization of Surface Defect in Carbon Steel Welded Sample: An Experimental Study

The Evaluation of Pulsed Eddy Current Technique for Detection and Characterization of Surface Defect in Carbon Steel Welded Sample: An Experimental Study

Numerical study of phase space analysis for the development of subsurface crack detection method using pulsed eddy current

Root-deck cracks, a prominent form of subsurface damage observed in orthotropic steel decks (OSDs), pose significant challenges to maintaining structural integrity. Early detection of these cracks is crucial to prevent further deterioration. This paper introduces novel and robust techniques for processing response signals obtained from the Pulsed Eddy Current Technique (PECT) using phase space analysis. The proposed methods aim to improve sensitivity and noise handling capabilities by employing an appropriate damage index derived from comprehensive phase space analysis, enabling effective detection of subsurface cracks in OSDs. A numerical study demonstrates the effectiveness of the proposed methods in detecting crack length change as small as 1 mm from the bottom of a 12 mm steel plate, with the Change in Phase Space Topology (CPST) identified as a suitable damage index. Furthermore, the newly proposed signal processing techniques allow for a more comprehensive interpretation of response signals for subsurface damage detection, encapsulating the extent of damage within a single value, even in the presence of small crack lengths near the bottom of the steel plate and noise. As a result, the proposed methods overcome the limitations of conventional approaches and offer promising prospects for enhanced subsurface crack detection in OSDs.

Enhanced Nondestructive Testing Using Pulsed Eddy Current and Electromagnetic Ultrasonic Techniques

Enhanced Nondestructive Testing Using Pulsed Eddy Current and Electromagnetic Ultrasonic Techniques

Quantitative Detection for Fatigue Natural Crack in Aero-Aluminum Alloy Based on Pulsed Eddy Current Technique

Aero-space aluminum alloys, as vital materials in aerospace engineering, find extensive application in various aerospace components. However, prolonged usage often leads to the emergence of fatigue natural cracks, posing significant safety risks. Therefore, research on accurate quantitative detection techniques for the cracks in aerospace-aluminum alloys is of vital importance. Firstly, based on the three-points bending experimental model, this paper prepared the fatigue natural crack specimen, and the depth of the natural crack is calibrated. Then, given the complexity of geometric characteristics inherent in natural cracks, the pulsed eddy current signal under the different natural crack depth is acquired and analyzed using an experimental study. Finally, to better exhibit the non-linearity between PEC signal and crack depth, a GA-based BPNN algorithm is proposed. The Latin Hypercube method is considered to optimize the population distribution in the genetic algorithm. The results indicate that the characterization accuracy reaches 2.19% for the natural crack.

Circular-arc array for the pulsed eddy current inspection of thermally insulated pipelines

The inspection of corrosion under insulation (CUI) has been identified as a significant challenge in the petroleum and chemical process industries. As some of the most effective strategies, pulsed eddy current (PEC) techniques have proved effective for the measurement of the CUI of pipelines. In this paper, we propose a circular-arc array (CAA) to improve the measurement efficiency for the PEC inspection of thermally insulated pipelines. Based on the PEC system model for inspecting the CUI of pipelines, the magnetic field distribution of the CAA with multiple excitors was investigated. It is shown that the coverage of induced magnetic field gets much larger than that of the single excitor to realize high-efficiency measurements. Moreover, a sparsely distributed receiver array is designed to further improve the signal-to-noise ratio by eliminating the waviness effect due to multiple excitors. Finally, experiments were conducted, and the results demonstrated the effectiveness of the proposed method for the inspection of thermally insulated pipelines.

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.

Analysis of PEC technique and external magnetic fields for detection of corrosion under insulation: 3D finite element model

Metal piping in industrial plants is subject to corrosion under insulation, which reduces the wall thickness and limits service life and operating conditions. The Pulsed Eddy Current (PEC) technique can be effective in the inspection of isolated metallic materials. However, changes in magnetic permeability make its use difficult in ferromagnetic steels. In this work, we used Neodymium magnets to magnetize the material during tests with a probe. We developed a 3D finite element model to reproduce the magnetic field of the PEC probe and identify defects under insulation. Theoretical results satisfactorily matched the experimental results.

The semi-analytic solution to the magnetic field of frequency-band-selecting eddy current testing for local corrosion flaw in large diameter pipeline.

Local corrosion flaws (LCFs) widely exist in large diameter pipelines (LDPs) (e.g. steam, oil/gas pipeline) due to flow-accelerated corrosion, environmental corrosion, and material aging. Frequency-band-selecting eddy current testing (FBS-ECT), as an improved eddy current technique (ECT), has rich harmonic components in exciting signals as a pulsed eddy current technique (PECT), as well as more effective utilization of electromagnetic energy by selecting a frequency band. It is expected that FBS-ECT has promising applications in detecting and evaluating the LCFs in LDP. Therefore, a solution to the magnetic field of FBS-ECT for LCF detection in LDP is of great concern to reveal the features of the FBS-ECT signal and the parameters of the LCF. Extending our previous work, the semi-analytic expression of the magnetic flux density for FBS-ECT in regions 1 and 2 (where the magnetic sensor is located) is deduced according to the superposition principle and TREE, the computation accuracy is validated by numerical simulation; next, a semi-analytic solution to the magnetic field of FBS-ECT for LCF in LDP is proposed; then, the sampling distance in FBS-ECT is optimized by considering the magnitude of △Bz and the sensitivity of △Bz with the LCF depth; finally, a case study is carried out to verify the optimal strategy and find the mapping relationship between the radius/depth and the FBS-ECT signal. The proposed semi-analytic solution for the magnetic field of FBS-ECT is not only helpful to understand the theoretical relationship of the magnetic field and LCFs with higher computation efficiency but also lays a theoretical foundation to promote FBS-ECT to apply in the characterization of other flaws in metal components.

A Magnetic Shielding-Type PEC Sensor With a Canister Structure and Magnetic Core

The pulsed eddy current (PEC) technique exhibits considerable benefits over conventional eddy current techniques. The structure and dimensional parameters of PEC sensors considerably influence the PEC systems. Conventional PEC sensors are susceptible to background noise of a magnetic excitation field. To strengthen the magnetic gathering ability and improve detection sensitivity, a magnetic shielding shell structure was introduced to PEC sensors. In this study, a novel canister structure and magnetic core-based PEC sensor with magnetic shielding was designed. Finite-element simulation and experimental study were performed subsequently to optimize the design. A 3-D finite-element simulation model was established according to the eddy current detection mechanism and electromagnetic shielding principle. The influence of the PEC sensor structure and size on its detection performance was observed. Next, a 2-D axis-symmetric model was established, and the size of this PEC sensor was optimized by using the orthogonal approach. The results revealed that the detection performance of this PEC sensor could be improved by incorporating an appropriate magnetic shielding mechanism and through the optimization of the sensor size. The research results show that compared with the PEC sensor without magnetic shield, the PEC sensor with magnetic shield developed in this article can obtain higher signal amplitude and can be better applied to surface and subsurface defect detection.

Using the Pulsed Eddy Current Techniques for Monitoring the Aircraft Structure Condition

Abstract It is known that during operation, the aircraft construction materials are exposed to significant mechanical loads and changes in temperature for a very short period of time. All this leads to various defects and damages in the aircraft assemblies and units that need to be inspected for the safe operation of the aircraft, their assemblies, and units. In some cases, the implementation of inspection or diagnostic is accompanied by the emergence of technical difficulties caused by the large size of the aircraft assemblies or units and limited access to their local places. Under such conditions, ensuring the possibility of diagnosis in hard-to-reach places of the object becomes especially important. The problem can be solved by applying wireless technologies. It allows spatial separation of the probes and the signal processing units, which simplifies the scanning of the surfaces of the large assemblies and units in hard-to-reach places. In this article, the description of the developed wireless system of eddy current inspection for aircraft structural materials is given. Experimental results of object scanning are given in the form of a distribution of the values of probe signal informative parameters (amplitude, frequency and decrement) along the object coordinates.

Quantitative evaluation of corrosion in conductors under stress via GPEC

Macroscopic defects such as corrosion in nonmagnetic Conductors Under Stress (CUS) are more universal than those within the zero-stress environment, and result in complicated characteristics regarding the electrical properties of the conductors. In this paper, Gradient-field Pulsed Eddy Current technique (GPEC) is intensively investigated for imaging and evaluation of corrosion in CUS. The influence of stress on electrical properties of nonmagnetic CUS with corrosion is analysed via multi-physics simulations and experiments. The correlations between characteristics of corrosion in CUS and the GPEC signal and its features are established and scrutinised. An image processing method reproducing defect images for quantitative assessment of detected corrosion in CUS is proposed.

Gradient-field pulsed eddy current imaging of hidden corrosion in layered conductors via Sparse Bayesian Learning alongside Baseline Estimation and Denoising with Sparsity

Layered structures of nonmagnetic materials such as the aluminium alloy are broadly used in the engineering field such as aerospace, energy, etc. Whereas, the corrosive environment leaves in-service layered structures inevitably prone to the subsurface corrosion which poses a severe threat to the structural integrity. Therefore, it is indispensable to quantitatively evaluate corrosion via non-destructive evaluation techniques. Gradient-field Pulsed Eddy Current technique (GPEC) has been found to be advantageous for high-sensitivity inspection of hidden corrosion. In this paper a Planar Current Sheet (PCS) probe of GPEC is proposed with the optimised trace layout for implementation of high degree of field uniformity. Following the acquisition of the raw corrosion image with the optimised GPEC probe, an image processing algorithm integrating the Sparse Bayesian Learning (SBL) with Baseline Estimation and Denoising with Sparsity (BEADS) has been proposed for reproduction of corrosion images conceiving the information regarding the corrosion-depth profile. The investigation via simulations and experiments reveals that through the 2D scanning of the proposed PCS probe of GPEC, the raw corrosion images and reproduced images derived by using the proposed SBL-BEADS algorithm simultaneously gives the comprehensive evaluation of the subsurface corrosion hidden within the layered structures in terms of the corrosion-opening and corrosion-depth profiles, respectively.

Uniform Circular-Array-Based Borehole Pulsed Eddy-Current System for Asymmetry Defect Inspection in Downhole Casings

The inspection of wellbore casings has been extensively investigated owing to the increasing concern for safety in oil and gas production. However, efficient techniques for inspecting asymmetry defects have not been achieved. In this study, we developed a uniform circular array (UCA) to address the problem of borehole pulsed eddy current (PEC) techniques for asymmetry defect inspection in downhole casings. Based on the borehole PEC system model, the UCA developed with multiple independent probes was designed to achieve asymmetry defect inspection, and the three-dimensional magnetic field data of borehole depths, circumferential azimuths, and sampling times could be obtained. Furthermore, a multichannel data acquisition circuit, which guarantees downhole operation at 150 °C, was developed for the synthesized UCA. Using azimuth dimension information from the synthesized UCA at a certain borehole depth, we obtained an inspection approach for the width and penetration depth of asymmetry defects in the circumferential and radial directions, respectively. Simulations and field experiments were conducted, and the results demonstrate the effectiveness of the proposed method in inspecting asymmetry defects.

Enhanced Feature Extraction Algorithms Using Oscillatory-Mode Pulsed Eddy Current Techniques for Aircraft Structure Inspection

Abstract A review of the existing literature shows that modern pulsed eddy current (PEC) technique for flaw detection in aircraft structure inspection is typically carried out in aperiodic mode. Аt 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 significant measurement errors. This article considers an advanced PEC 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 and analyzed. The frequency and attenuation coefficient of natural oscillations are proposed as the informative parameters of the probe signals. The obtained mathematical model of the probe signals allows for the dependence of proposed signal parameters on the characteristics of the testing object to be evaluated. Herein, we first develop algorithmic software for determining and analyzing the discrete amplitude and phase characteristics of PEC NDT signals based on the simulation results. The errors of the natural frequency oscillations and the attenuation coefficient determination as well as the optimal time for its determination are analyzed in order to minimize the possible errors. Next, the proposed informative parameters are experimentally investigated using a set of specimens. The obtained results confirm the possibility of the proposed methodology to enhance the inspection procedures related to the electrical conductivity and geometric parameters measurements as well as the detected defect sizing.

Simultaneous measurement of thickness and lift-off using the tangential component of magnetic flux density in pulsed eddy current testing

The pulsed eddy current (PEC) technique is commonly used in the petrochemical and power generation industries to measure two parameters: the degree of pipe wall corrosion and the thickness of the insulation shield. These two parameters can be evaluated by examining the thickness of conductive materials and the lift-off distance, respectively. To explore a possible technique for simultaneously measuring the thickness and the lift-off, the present study envisaged the development of a PEC testing method based on detecting the tangential component of the magnetic flux density. The tangential component of the magnetic flux density was excited by two racetrack-type coils injecting currents in opposite directions that were picked up by a magnetic sensor. The slope in logarithmic scale and the time-to-peak of the magnetic signal were verified to characterise the features of the thickness and the lift-off, respectively. By analysing the simulation and experimental results, the feasibility of simultaneously measuring the thickness and the lift-off was demonstrated.

Методика на основе импульсных вихревых токов для определения механических свойств ферромагнитных материалов

In the current steel industry production, the detection of the mechanical properties of ferromagnetic materials relies on destructive testing, which greatly increases the cost of production. In this paper, a method is proposed to estimate the mechanical properties of ferromagnetic materials based on the pulsed eddy current (PEC) techniques. Firstly, the traditional features of the PEC signal, such as differential signal peaks and spectral amplitudes, are applied to the quantitative estimation of mechanical properties. Secondly, a method based on the empirical mode decomposition and Hilbert-Huang transform is used to extract the marginal spectral peak and marginal spectral energy as new features. Finally, BP neural network algorithm is introduced to quantitatively estimate the mechanical property parameters. The results show that the combination of both traditional and new features is suitable for mechanical properties estimation. The method has high accuracy for the quantitative estimation of mechanical performance parameters.

Bobbin pulsed eddy current array probe for detection and classification of defects in nonferromagnetic tubes

The pulsed eddy current technique has received a great deal of attention in recent decades. To improve its performance and applicability, several kinds of probes, such as rectangular and gradient field probes for plate detection and encircling probes for tube detection, have been proposed. However, few bobbin-type pulsed eddy current probes have been proposed. This study proposes a bobbin pulsed eddy current array probe to simultaneously detect, classify and evaluate inner and outer surface defects in nonferromagnetic tubes. The probe contains double exciting coils and 20 sensors. The double exciting coils could generate stronger and more uniform induced eddy current in tube. The 20-sensors array could measure the complete circumferential magnetic signals above tube inner surface. Using the Br curves drawn by peak value and post peak value, inner and outer surface defects can be classified without beforehand training or the usage of complex process. Meanwhile, the maximum value in Br curve can be used to measure the defect depth and residual depth accurately.

Defect Characterization in Layered Composites using a Pulsed Eddy-Current Technique

The practical possibility of determining the size of the delamination area and its depth of location in nonmetallic multilayer low-conductive materials is demonstrated using the unique pulsed eddy current equipment facilities. Operational integrity and efficiency of the application of the developed techniques and engineering solutions are confirmed by the results of the experimental studies performed on the carbon-fiber-reinforced plastic specimens with artificial defects in the form of delaminations varying in sizes and shapes.

Novel Time-Domain Parameters for Detection and Classification of Flaws Using Pulsed Eddy Current Technique

Pulsed eddy current (PEC) testing is an electromagnetic nondestructive evaluation (NDE) technique which is used for detection and classification of flaws. This paper presents an approach for the extraction of novel timedomain flaw parameters viz. amplitude ratio (V₁/VSUB0/SUB) and time constant (τ) for detection and classification of different flaws. Experiments are carried out on stainless steel (SS-316) plate with artificial EDM notches whose width (1.0 mm & 3.0 mm) and depth (1.0 mm to 6.0 mm) varied. The proposed approach can classify both surface and sub-surface flaws in an 8.0 mm thick SS plate. The advantage of the proposed approach is that it doesn’t require a reference signal subtraction or signal processing methodologies for the detection and classification of flaws.

Investigation on Velocity Effect in Pulsed Eddy Current Technique for Detection Cracks in Ferromagnetic Material

Nondestructive testing (NDT) for ferromagnetic material under motion condition is a challenging topic, because the distribution of the magnetic fields inside the ferromagnetic material is more complicated due to motion-induced eddy current (MIEC) and ferromagnetic material magnetization. Therefore, a fast, accurate, and automatic NDT technique for quantitative detection of crack in the moving ferromagnetic material is an urgent issue. Currently, the pulsed eddy current (PEC) technique is widely applied in quantitative crack characterization in metals; however, the literature focus on the investigation of the velocity influence on PEC is rare. This article performs a deep investigation on the velocity effect of PEC technique by numerical simulation and experiments, and the relationships of speed and PEC signal are discovered. The results show that the velocity effect can change the baseline value of the detection signal in the PEC detection system. Moreover, the crack location, width, and depth can be characterized by PEC with high speed when crack appears in the high-level stage of the excitation signal, and in contrast to static PEC testing, motion detection has a stronger capability to characterize the crack depths. Based on the results, it is beneficial to propose a new high-speed inspection technique for crack characterization in ferromagnetic material components, such as rotating metal components, pipelines, and rail tracks.