Pulsed Eddy Current Detection Research Articles

Modelling and experimental study on pipeline defect characterisations using a pulsed eddy current measurement

ABSTRACT Pipelines are widely used as the main transportation method in petrochemical and metallurgical industries. However, the special nature of the materials transported in pipelines means they are often subjected to high temperature, high pressure and corrosive conditions. This can lead to defects, such as thinning and cracking, resulting in pipeline failure and causing serious economic losses. Therefore, regular non-destructive testing of pipelines is particularly important. This paper uses the non-destructive testing method with pulsed eddy current technology to characterise pipeline thinning and defects. A preliminary study is conducted on the pulsed eddy current detection signal patterns for pipeline crack defects with varying orientations and quantities. A more portable pulsed eddy current detection device with an extended wall thickness detection range is developed. It can achieve measurements with a maximum thickness of 30 mm for detections of pipelines with rectangular defects and thickness-stepped reduced. The experimental results are consistent with modelling results, and the accuracy for pipelines with insulation layer is also investigated. On-site measurements using the PEC system are conducted on equipment sections with pipe thickness within 20 mm in a petrochemical plant. It is confirmed that the developed PEC inspection device can accurately characterises the thickness of pipelines with 0–50 mm cladding.

Finite element simulation study of signal characteristics of pulsed eddy current detection technology

Finite element simulation study of signal characteristics of pulsed eddy current detection technology

Research on Deep Defect Detection Method of Cable Lead Sealing Based on Improved Pulsed Eddy Current Excitation

In order to reduce power failures caused by lead sealing defects, it is necessary to carry out nondestructive testing of cable lead sealings. However, previous studies have focused on the detection of surface and near-surface defects of lead sealings. Thus, an improved pulsed eddy current detection (IPECD) method is introduced to detect the deep defects of cable lead sealings (with depths ranging from 6 to 12 mm), and the frequency range selection principle and the optimization method of initial phase angles of different frequency components of IPECD, used to maximize the peak value of the excitation signal, are first explained in detail. Then, the detection sensitivities of the deep defects before and after the optimization are compared and analyzed based on a simulation. Finally, using the IPECD method, experiments are conducted to study the effects of the defect depth on features of the lift-off point of intersection and the zero-crossing time, enhancing the foundation for the prediction or rapid detection of the depth of lead sealing defects.

Effects of the wire mesh on pulsed eddy current detection of corrosion under insulation

ABSTRACT Pulsed eddy current (PEC) technique has been used to detect corrosion under insulation (CUI) for decades, but whether and how the wire mesh laid in the insulation layer affects the detection remains ambiguous. This paper touches on this issue for the first time. The insulated structure was simplified to a carbon steel plate covered by a cladding with an air gap representing the insulation layer, in which the wire mesh was situated. Finite element simulations were performed on the simplified model and found that the aluminium or stainless steel wire mesh had little effect on eddy currents in the plate, while the mild steel wire mesh could cause a considerable increase in the probe footprint and a significant drop of the eddy current density. For the mild steel wire mesh, the magnetic permeability and wire diameter were the main factors affecting the probe footprint and eddy current density. Afterwards, simulations were conducted to analyse the effect of the mild steel wire mesh on the PEC probe performances for evaluating the CUI depth and found that the mild steel wire mesh led to decreases in both the PEC signal amplitude and decay rate. The simulation results were finally verified by experiments.

Optimization design of excitation coil for pulsed eddy current testing of laser welding defect structure of power battery bus-bar

Pulsed eddy current testing is suitable for non-contact detection of conductor structural defect, which is an effective method to realize online detection of welding structural defect of power battery pack. Aiming at the circular laser weld structure between the bus-bar and the terminal of the power battery pack, a three-dimensional finite element simulation model of pulsed eddy current testing is established. According to the structural parameters of the pulsed eddy current excitation coil, which are the inner diameter, outer diameter, height and number of turns, the pulsed eddy current voltage responses of the laser welding defect structure of the battery pack bus-bar are calculated, respectively. By analyzing the influence of the excitation coil parameters on the pulsed eddy current detection results, the pulsed eddy current excitation coil parameters are determined for the testing of laser welding structural defects. It provides a method and basis for the optimal design of the pulsed eddy current detection system for the laser weld structural defect of the battery pack bus-bar.

Signal Processing and Defect Characterization of Pulsed Eddy Current Testing Based on Cross-Correlation

In order to solve the problems of the low signal-to-noise ratio and inaccurate feature extraction of time domain signal in pulsed eddy current detection, a method of signal processing and feature extraction for pulsed eddy current detection based on cross correlation is proposed. the pulsed eddy current testing of cracks in different sizes and positions of multi-layer aluminum alloy specimens is carried out by using magnetic differential probe based on Tunnel Magnetoresistance sensor (TMR). Experimental results show that compared with the traditional method, the proposed method can characterize the defects at different position depths more clearly and accurately, which improves the detection depth and accuracy of pulsed eddy current detection. According to the variation rule between the size and depth of the defect and the cross-correlation eigenvalue, the exponential change curve of peak-to-peak time of cross-correlation can be determined, which can effectively identify the defects exceeding the geometric size of threshold at different depths.

Research on Application of Pulsed Eddy Current Testing in Nuclear Power Plant Pipelines

The condensate pipelines, main water supply pipelines, drain pipelines, and partial extraction pipelines of nuclear power plants are all coated with coatings on the outside of the pipelines to improve heat exchange efficiency. At present, the detection methods of ferromagnetic pipelines are mainly conventional ultrasound and ultrasonic guided waves. It is necessary to remove the insulation layer of the outer wall of the pipeline before the inspection, which leads to a prolonged inspection period and increased labor costs. This paper uses the measured and calculated values of the induced voltage to establish the optimal parameter inversion problem and combines the coupling relationship between the parameters to propose a reliable pulsed eddy current detection method for the relative wall thickness of ferromagnetic pipes. Using the pulsed eddy current detection method for the relative wall thickness of ferromagnetic pipelines proposed in this paper, the scanning detection of nuclear power plant steel pipes is compared with conventional ultrasonic testing. The detection results are reliable and suitable for non-destructive testing and evaluation of nuclear power plant ferromagnetic pipeline wall thickness corrosion thinning.

Feature Engineering of Time-Domain Signals Based on Principal Component Analysis for Rebar Corrosion Assessment Using Pulse Eddy Current

Corrosion of steel rebars in reinforced concrete impacts structural integrity of the infrastructure. While several Non-Destructive Testing and Evaluation (NDT&E) techniques exist for corrosion monitoring in structures, there is a need for cost-effective solution for early detection of sub-surface corrosion of rebars in civil infrastructure. Here we present a low-cost corrosion sensing system based on pulsed eddy current detection using anisotropic magnetoresistive (AMR) sensor to detect the corrosion in steel reinforcing bars. A novel probe with large figure of merit ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$21.62\times6$ </tex-math></inline-formula> m <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{T}^{-1}$ </tex-math></inline-formula> ) is presented, that can detect corrosion in 20 mm diameter rebars at lift-off distances as high as 55 mm with low excitation current of 0.2 A. The sensitivity is enhanced by using area under the curve of various segments of the time-domain sensor output as features. Optimal feature selection and dimensionality reduction, as well as quantitative estimation of extent of corrosion are demonstrated using principal component analysis.

A review of two types of non-destructive testing technique for pressure pipelines

Pulsed eddy current testing (PECT) and electromagnetic ultrasonic non-destructive testing (NDT) techniques are important methods for detecting defects in pressure pipelines. Although these methods have the advantages of no contact requirement, fast detection and simple signal processing, there is a near-surface blind area in electromagnetic ultrasonic detection and pulsed eddy current detection cannot accurately detect deep locations due to the skin depth. However, these two techniques can be combined to potentially overcome their individual limitations. This paper presents an in-depth study of the use of pulsed eddy current testing and electromagnetic ultrasonic non-destructive testing techniques to detect defects in pipelines. Moreover, the basic principles, numerical simulation methods, testing systems and application characteristics of the individual methods and their combined use are discussed.

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.

Thickness and Conductivity Measurement of Multilayered Electricity-Conducting Coating by Pulsed Eddy Current Technique: Experimental Investigation

Electricity-conducting coatings are widely applied in industries, such as thermal barrier coating in the aerospace field. Therefore, it is necessary to detect the thickness and the conductivity of the coatings to ensure the quality of the coating. Extended on the existing work on the coating and conductivity detection by the traditional eddy current (EC) technique, this paper investigates the feasibility of the pulsed EC (PEC) technique in coating conductivity and thickness detection. For the single-layered electricity-conducting coating, the coupled influence of the coating conductivity on the relationship between the coating thickness and the PEC detection signal is deeply analyzed, and the approach to detect the coating thickness and conductivity for single conductivity coating is proposed; for the multiple-layered coating, the coupled influence of the coating thickness on the relationship between the other coating thickness and the PEC detection signal is analyzed, and the approach to detect the two-layered electricity-conducting coating thickness is proposed. Finally, a decoupling inversely detection method is proposed to obtain the coating thickness and conductivity, which overcome the singularity of the equation solving method. The results show that the average relative errors of the inverse detection are within 7%. Therefore, the PEC technique can be readily applied to detect the thickness and conductivity of the multiple-layered electricity-conducting coating in spacecraft, pipeline, and high-speed cutting tools.

Principle Analysis of Soil Electrical Conductivity Test Based on Pulsed Eddy Current

Nowadays, soil salinization is one of the major environmental geological disasters in the world. The rapid survey of soil conductivity through pulsed eddy current detection helps reflect the salinization degree, which can save cost and improve efficiency. In this paper, the basic principle of pulsed eddy current for soil conductivity detection is expounded, the detection depth of pulsed eddy current is theoretically analyzed, and the principle of soil conductivity detection based on pulsed eddy current is studied as well as analyzed.

Study on Detection Methods of Residual Wall Thickness for Process Pipeline Corrosion in Oil and Gas Gathering and Transportation Station

In this paper, it is proposed to adopt Pulsed Eddy Current (PEC) testing of coaxial double coil structure to implement the detection on residual wall thickness of pipeline corrosion in oil and gas gathering and transportation station, in the view of reduction of wall thickness caused by corrosion. The electromagnetic field theory is applied to conduct theoretical analysis on PEC detection. On such basis, a theoretical model of coaxial double coil structure for PEC detection is built, and the relation of voltage phase of the detected signal varying with the wall thickness of the pipeline is derived. Then a method for evaluating the residual wall thickness of pipelines based on the phase trough time of PEC signals is proposed. Moreover, the parameters of the PEC probe are optimized by finite element method, and the detection system is designed accordingly. As a result, the practicability of the detection system and the correctness of the theoretical model are verified by experiments, proved that the model can realize the detection of the residua wall thickness under the condition of different media transported by the pipeline.

Pulsed Eddy Current Detection of Cracks in Multilayer Aluminum Lap Joints

Aging aircraft is susceptible to cyclic fatigue cracks around ferrous fasteners in multilayer aluminum wing lap joints, as found on Canadian Military aircraft CP-140 Aurora and CC-130 Hercules. Current methods of crack detection utilize bolt hole eddy current, requiring fastener removal, a time consuming process that also has the potential to result in collateral damage. In this paper, pulsed eddy currents (PECs) are induced in the aluminum wing structure by a probe centered over a ferrous fastener. The response signals are analyzed using a modified principal components analysis (PCA) and cluster analysis to show separation of groups of PCA scores from fasteners with and without notches in the bore hole. The Mahalanobis distance (MD), a cluster analysis method, is used to obtain a relative distance measurement between scores associated with cracks from those without cracks. The MD evaluation provides confidence intervals for detection of cracks, which range in extent from fastener holes from 0.9 to 5.5 mm, and a means of potentially sizing larger (>3 mm) second layer cracks. In this paper, 100% of the cracks in the sample were detectable. The results demonstrate PEC as a viable technique for second layer crack detection with ferrous fasteners present.

Pulsed eddy current detection of cracks in F/A-18 inner wing spar at large lift-off using modified principal component analysis

Stress corrosion cracks may develop between fasteners in the aluminum inner wing spars of F/A-18 (CF188 Hornet) aircraft. These fasteners secure carbon-fibre/epoxy composite wing skin, of varying thickness (8 to 21 mm), to the spar. Inspection of the spar through the wing skin is required in order to avoid wing disassembly. A pulsed eddy current system that uses principal component analysis and discriminant analysis to identify cracks has been field tested at the USN North Island facility. The results show that the system can accurately identify cracks in real time throughout the wing. The method is far faster than X-ray radiography and, because it is very portable, can be readily deployed to second or first line facilities. Issues that need to be addressed to improve the performance of the system are identified and potential solutions are examined.

Surface Crack Detection for Carbon Fiber Reinforced Plastic Materials Using Pulsed Eddy Current Based on Rectangular Differential Probe

Aiming at the surface defect inspection of carbon fiber reinforced composite, the differential and the direct measurement finite element simulation models of pulsed eddy current flaw detection were built. The principle of differential pulsed eddy current detection was analyzed and the sensitivity of defect detection was compared through two kinds of measurements. The validity of simulation results was demonstrated by experiments. The simulation and experimental results show that the pulsed eddy current detection method based on rectangular differential probe can effectively improve the sensitivity of surface defect detection of carbon fiber reinforced composite material.

Real Time Pulsed Eddy Current Detection of Cracks in F/A-18 Inner Wing Spar Using Discriminant Separation of Modified Principal Components Analysis Scores

The aluminum inner wing spars of F/A-18 Hornet aircraft may undergo stress corrosion cracking along the spar between the fasteners that secure carbon-fiber/epoxy composite skin to the wing. Inspection of the spar through the wing skin is required to avoid wing disassembly. The thickness of the skin varies between 9 and 21 mm (0.36-0.83 in) and fasteners may be either titanium or ferrous. Pulsed eddy currents (PECs), generated by a probe centered over the fastener, demonstrate the capability of detecting simulated cracks within spars with the wing skin present. Comparison of signals from separate pick-up coils, mounted to either side of the excitation coil, is used to detect differences in induced eddy current fields, which arise in the presence of cracks. To overcome variability in PEC signal response due to variation in: 1) skin thickness; 2) fastener material and size; and 3) centering over fasteners, a large calibration data set is acquired. Multidimensional scores from a modified principal components analysis (PCA) of the data are reduced to 1-D using a discriminant analysis method. Under inspection conditions, calibration PCA scores combined with discriminant analysis permit rapid real time go/no-go PEC detection of cracks in F/A-18 inner wing spar.

Pulsed eddy current detection of cracks in F/A-18 inner wing spar without wing skin removal using Modified Principal Component Analysis

Stress corrosion cracks may develop between fasteners in the aluminum inner wing spars of F/A-18 Hornet aircraft. These fasteners secure carbon-fibre/epoxy composite wing skin, of nominal 13mm thickness, to the spar. Inspection of the spar through the wing skin is required in order to avoid wing disassembly. Pulsed eddy currents, generated by a probe design that utilizes the ferrous fastener as a flux conduit, are demonstrated as having the capability of detecting simulated cracks within the spar with the wing skin present. Differentially connected pickup coils are used to sense differences in response due to asymmetries in induced eddy current fields arising in the presence of cracks. To overcome variability in PEC signal response due to variability in magnetic coupling to the fastener, a large measurement set was analyzed using Modified Principal Component Analysis (PCA). The modified PCA minimizes residual sum of squares to extract eigenfunction scores, which are used to detect the presence of cracks ending on one side of the fastener hole. The ability of the method to sense simulated cracks independent of confounding measurement parameters was demonstrated.

Data fusion algorithm for pulsed eddy current detection

A weighted data fusion algorithm based on matching pursuit (MP)-wavelet packet (WP) atomic decomposition and its applications in pulsed eddy current (PEC) non-destructive testing systems for estimation of feature parameters is presented. MP-WP atomic decomposition is used to estimate each noise-free pulse response from its noisy observation of a single-sensor PEC probe and obtain the peak value parameter from each estimated response. A weighted data fusion algorithm, on the basis of minimum mean square error (MMSE), is applied to fuse each obtained peak value together to get final optimum parameter estimation. Based on the difference of each noisy pulse response and its estimation, the variance of noise in each pulse response can be computed, respectively. Accordingly, the weight of each pulse response for data fusion is calculated by the variance of its noise. Finally, the peak value parameter is estimated by the utilised data fusion algorithm. In terms of MMSE, this weighted fusion presents an optimum estimation of the feature parameter of multi-pulse responses of PEC sensor, compared with normal averaging process.