Eddy Current Inspection Research Articles

How to use eddy current technology to test ferrous and non-ferrous wire

Eddy Current inspection is a technique used for detecting surface seams, cracks, pits, slivers and internal discontinuities in ferrous and non-ferrous wire. Different test sensor configurations including encircling coil and rotary probes can be used. When using encircling coil eddy current testing, the wire passes through the coil excited by an alternating current with one or more Drive signals. Rotary probe inspection can reliably detect surface seams and cracks using eddy currents which are induced by one or more probes traversing the surface of the material under test. Wire sizes can range from ultra-fine below .002” (.051mm), fine wire .002” (.051mm) to .005” (.127mm), standard wire .006” (.152mm) to .725” (18.42mm). Encircling coil testing can be used for the whole range whereas Rotary probe inspection can only be used above .200” (5.08mm).

Qualification of Bolt-Hole Eddy Current Inspections Using Numerical and Experimental Input

Qualification of Bolt-Hole Eddy Current Inspections Using Numerical and Experimental Input

Design and application of portable eddy current inspection device for thimble tubes of nuclear power plant

Abstract The Thimble tube is an important piece of equipment in the nuclear power plant; its role is to provide a neutron flux detector with a channel for the reactor fuel assembly. Eddy current detection is the main way to evaluate and track the wear of the thimble tube. In order to conduct more efficient detection of the thimble tube, this paper has carried out a series of studies on the mechanical device of the eddy current detection of the thimble tube and the software control system. The inspection system is compact, portable, and does not require an external power supply or gas source, making it easy to carry and operate. It is well-suited for promotion in various nuclear power plants.

Portable Eddy Current Inspection System with Real-Time SVM Classification of the Aging States of Steam Reforming Furnace Tubes

Portable Eddy Current Inspection System with Real-Time SVM Classification of the Aging States of Steam Reforming Furnace Tubes

Oxygen corrosion of reboiler tube served in production of dilution steam from heat exchanger of petrochemical refinery

This paper reports the oxygen corrosion of heat exchanger tubes serviced in dilute steam generation system. The floating head heat exchanger employed in a petrochemical industry underwent remnant corrosion failures particularly at lower passes of tube bundle. Initially remote field eddy current inspection technique was employed for tube bundle conditional assessment and further, root cause of degradation of tube had been analyzed. Comprehensive experimental techniques including visual examination, tube chemistry analysis, external tube surface morphological analysis, elemental mapping, scanning electron microscopy, light microscopy and x-ray diffraction studies were employed. The tube surface at the degraded position with its cross sectional examination was rigorously evaluated as well. Moreover, actual steam parameters such as pH, conductivity and iron & chloride concentration have been monitored in the petrochemical facility. The detailed analysis concluded that dissolved oxygen in boiler feed water (BFW) was the root cause for corrosion failure. Several other foreign elements were detected and source of each element was discussed in the context of actual heat exchanger operating conditions. Simulated conditions of BFW service have electrochemically been evaluated in two different dissolved oxygen concentrations at 7.5 ppm and 12.7 ppm, respectively. Even small increase of dissolved oxygen in BFW could lead to promotion of oxygen reduction reaction. Theoretically SA179 tubes operated at pH of 9.75 could lead to formation of bicarbonate and it could protect the tube in absence of dissolved oxygen as evaluated by Molecular Dynamics simulation. However, according to obtained results, tube has been degraded due to presence of dissolved oxygen in BFW. Various contributing factors such as external paint/coat removal, absence of de-aerator system in BFW treatment and improper corrosion inhibitor programme were discussed. Several practical countermeasures have been suggested to mitigate oxygen corrosion failure in petrochemical refineries.

Design and Analysis of Micro Signal Detection Circuit for Magnetic Field Detection Utilizing Coil Sensors

Eddy current inspection has been extensively employed in non-destructive testing of various conductive materials. The coil probe, as a mainstream sensor in the eddy current detection system, inevitably encounters interference from external signals while transmitting its own signal. Therefore, developing techniques to extract valuable signals from noisy ones is crucial for ensuring accurate detection. Carbon fiber composites not only possess significantly lower electrical conductivity compared to conventional metallic materials but also exhibit notable anisotropy. To address this issue, we designed an ‘8’ coil probe set where the excitation coil does not electromagnetically interfere with the detection coil. However, practical applications that require portability and miniaturization pose challenges when utilizing this coil probe set to identify carbon content or defects due to the typically weak output signal. To address this issue, this paper proposes a design that combines the ‘8’ structure of the planar coil probe with the principle of phase-locked amplification to create a dual-phase sensitive phase-locked amplification detection circuit. These specific design ideas were tested using a weak signal, which passed through the preamplifier, secondary amplifier, and band-pass filter comprising the target channel for signal amplification and noise filtering. The effective signal amplitude is proportional to the inverse phase difference between the direct current (DC) signal and inversely proportional to the amplitude of the signal. Finally, the DC signal was passed through an analog-to-digital converter (ADC). The analog-to-digital converter (A/D) is used to collect and calculate the DC signal, enabling the detection of weak electrical signals. Simulation experiments demonstrated that the signal detection circuit has an amplitude error below 0.2% and a phase error below 0.5%. The phase-locked amplification circuit designed in this paper can effectively extract the tiny impedance change signals of the planar coil sensor probe with high sensitivity and good robustness.

RHiREM: Intelligent diagnostic framework for pipeline Eddy Current Internal Inspection based on reinforcement learning with hierarchical reward exploration mechanism

Pipeline safety is of paramount importance for socio-economic development, necessitating regular inspection and maintenance. The complexity of the internal pipeline environment and the presence of irregular noise in detection data, however, pose significant challenges to pipeline inspection technologies. Additionally, the reliance on manual expertise for inspection and the absence of standardized assessment criteria further complicate the development of automated inspection methods in this context. To address these challenges, this paper proposes a pipeline anomaly detection framework based on reinforcement learning with hierarchical reward exploration mechanism (RHiREM). It includes two main aspects: Firstly, the hierarchical reward mechanism. By deeply simulating the process of defect recognition based on expert personal experience, the original pipeline data is first adaptively divided into sets of windows with different sizes, and then attribute and type judgments are performed on them. In this way, the approach achieves accurate identification of defects and pipeline structures in scenarios with minimal noise interference. Secondly, the hierarchical exploration mechanism. By leveraging the temporal exploration and spatial exploration, the mechanism enables further deep search and feature learning on complex pipeline signals, and facilitates comprehensive assessment of the relationships between global features and local features across different signals, effectively resolving the difficulties associated with identifying defect signals in the presence of high noise interference. the proposed framework has been demonstrated to automate the detection of complex on-site pipeline internal signals and successfully detected the common anomalies with high F1-score over conventional techniques.

Preliminary assessment of the feasibility of field evaluation of heat exchanger tube structure using ultrasonic guided wave with exterior approach

The integrity of heat exchanger (HE) tubes is essential for power plant safety and efficiency. Numerous tube assessment techniques have been proposed, including eddy current inspection and the guided wave method. However, they mainly evaluate from the inside of the tubes. Hence, when the interior region of a tube wall is not accessible, inspection is difficult. To overcome this issue, a new guided wave device is fabricated that inspects from the exterior of the heat exchanger tubes. Using this device, a few sample heat exchanger tubes are selected and inspected in a field evaluation during an overhaul period. Furthermore, the feasibility of the device is evaluated. This new approach is expected to contribute to the efficient evaluation of heat exchanger tubes.

Fastener hole inspection using 2D phased array

Fastener hole cracks, resulting from stress concentration around the hole, are potential sources of failure in mechanical structures. Traditionally, inspection involves manually moving a single ultrasonic probe around the hole or using an eddy current probe to move through the hole. However, single ultrasonic probe inspection is time-consuming and needs skilful operators. Eddy current inspection requires the removal of the fastener in advance and does not allow easy crack sizing and visualization. This paper proposes a novel approach that combines a 2D phased array with a coupling block to enable complete fastener hole inspection from a single array position. A single full matrix capture (FMC) data set is collected, from which 3D volumetric images are formed. To obtain clear images of the geometry and potential defects, half-skip and multi-skip total focusing method imaging algorithms are investigated together with transmitter–receiver pairs selection methods to detect different target features. Experimental results demonstrate that the proposed inspection approach can eliminate dead zone problems and capture all target information from a single inspection position. These methods show great potential in enhancing the efficiency and reliability of fastener hole inspections.

Research of eddy current inspection system for condenser titanium tubes in nuclear power plant

Condenser titanium tubes are easily to generate many defects in nuclear power plants, such as corrosion, damage, and wall thickness thinning. Eddy current technology is the main method of condenser titanium tubes in-service inspection, but manual operation has the problem of low efficiency. This article designed one new titanium tube eddy current inspection system based on automatic push-puller, and successfully applied in the nuclear power plant in China. The results show that this system can realize eddy current inspection in the condenser tubes with push-puller machine.

Surface Integrity Evolution in Grinding by means of In-Process Eddy Current Inspections

The in-process detection of grinding burns has earned considerable interest from both researchers and industries in recent years. Various Non-destructive testing (NDT) technologies, including Eddy Current (EC), Barkhausen Noise (BN), and Acoustic Emission sensors (AE), have been employed to address this issue, yielding successful results for specific applications. However, a comprehensive understanding of burn generation and its prevention in grinding operations remains an area of interest that has not yet been fully resolved.This paper focuses on investigating the electromagnetic response of a custom-made EC sensor applied to UNE F-522 (AISI 01) steel during in-process inspections. Experimental grinding tests have been performed using a special EC inspection head installed in the grinding machine. The impedance change of the material during grinding is discussed in terms of the machine out-puts (Power consumption) and other grinding variables, such as number of passes, the roughing stock removal, and the finishing strategy. The experimental results demonstrate that the proposed EC technology not only enables the detection of burns, but also enhances comprehension of the surface integrity changes occurring during the grinding process.

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.

Classification and Sizing of Surface Defects in Pipelines Based on the Results of Combined Diagnostics by Ultrasonic, Eddy Current, and Visual Inspection Methods of Nondestructive Testing

Classification and Sizing of Surface Defects in Pipelines Based on the Results of Combined Diagnostics by Ultrasonic, Eddy Current, and Visual Inspection Methods of Nondestructive Testing

Modelling of wear defects under Anti Vibration Bars in U-bend for the Eddy Current inspection of Steam Generator tube

The purpose of the anti-vibration bars (AVBs) positioned on both sides of the U-bend part of the steam generator tubes is to limit the vibratory phenomena. These tubes are prone to localized rubbing against the AVBs, resulting in friction-induced wear. To address this issue, eddy current (EC) monitoring and analysis tools like simulation are developed [1]. The objective of the joint study conducted by CEA LIST and IRSN, is to simulate the wear signal under the AVB and to assess the influence of the main geometric parameters on this signal. Within this context, new advanced geometric tools, such as the vibratory movement of an object have been developed to enhance the CIVA model developed at CEA LIST, [2][3]. This 3D numerical model has been experimentally validated on simple configurations involving a machined tube with rectangular-bottomed flats and an AVB, inspected by two axial bobbin coils. The obtained results demonstrate that the presence of AVBs significantly influences the signature of defects near them, especially for thin defect.

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.

Cause Analysis of Leakage Failure of Seamless Steel Pipe during Pipeline Pressure Test

By means of chemical analysis, tensile test, metallographic analysis, and energy spectrum analysis, the leakage causes of seamless steel pipe in the process of pipeline pressure test were analyzed. The analysis shows that the crack of steel pipe appears before rolling, and the non-metallic inclusions near the crack are the crack source or preferred path of steel pipe cracking. The leakage of steel pipe defects in the subsequent eddy current and ultrasonic inspection is one of the main reasons the unqualified steel pipe flows into the construction site and leads to the leakage of the pressure test.

Latest Developments in the Hardspot Inspection of heavy plates

Hard Spots are local areas with increased hardness on the surface of semi-finished or end products in steel manufacturing. The cause of these hard spots is attributed to effects in the casting or rolling process. In general, the occurrence of hard spots cannot be avoided completely in production of heavy plates. Therefore, in various current line-pipe specifications the topic ‘hard spots’ is discussed and there is actually a strong request for a suitable test method from end users as well as manufacturers of line pipes. The current presentation should give an update on the ongoing developments. Basis of all current approaches are electromagnetic inspection methods, based on the correspondence in between electrical and magnetic material properties and physical hardness. To be able to integrate an inspection into the production process, the so called rolling skin or mill scale, a thin surface layer of different iron oxides with different material properties to the base material, should not influence the inspection results. The inhomogeneities of this rolling skin, especially in conductivity and permeability, normally render standard eddy current inspection impossible. Additionally in the standard production process, the products were handled by large cranes, manipulating the plates by strong magnets. These magnets leave behind a significant residual magnetization. To overcome both problems the method uses a strong alternating magnetization to measure different resulting micro magnetic parameters. By combining these parameters, the mill scale as well as the residual magnetization effects can be minimized, so it gets possible to measure small local hardness variations on the plates. The presented paper describes the actual progress of the inspection method itself including the theoretical background as well as the calibration on artificial hard spots. Furthermore, an outlook will be given to the implementation in an automatic inline inspection system for plate mills.

Quality assessment of SUS316L fabricated by metal additive manufacturing with eddy current inspection

Guaranteeing the quality of additive manufacturing (AM) components after fabrication is very important. In this study, a discrete non-destructive evaluation (NDE) system that includes an eddy current testing (ECT) probe and a fluxgate sensor was developed. In conventional ECT, the defect detection depth is limited by the skin depth of the material under investigation and requires a high frequency of the order of MHz. However, in the NDE system, the high sensitivity of the fluxgate sensor and the use of an ECT coil make it possible to detect subsurface defects at a relatively low frequency. A double-excitation coil was used to excite eddy currents in the specimen at relatively low frequencies, whereas a planar differential coil was used as a pick-up loop connected to an input coil that was inductively coupled to the fluxgate sensor. Based on the developed NDE system, five stainless steel (SUS316L) specimens fabricated by powder bed fusion were inspected. A strong correlation was observed between the detected signals and internal porosity, which was confirmed using X-ray computed tomography images. Although this approach cannot detect the local existence of defects, it can be applied for quality assessment, such as density and distribution of porosity in metallic parts fabricated by AM.

Applicability of simulation-assisted probability of detection analysis considering multiple signal features to eddy current testing of weld

In this study, a simulation-assisted probability of detection (POD) analysis that considers multiple flaw parameters and signal features is presented, including an evaluation of its applicability to eddy current testing for weld inspection. In the proposed method, both the real and imaginary parts of eddy current signals were considered, unlike conventional methods that only consider signal amplitude. Type 304 stainless steel plates were joined by butt welding, and slits were fabricated on the weld path. The eddy current inspection was conducted using a uniform eddy current probe. Numerical simulations were also performed using the finite element method, with the model imitating the experimental situation. The POD contours were calculated using the proposed method, and they exhibited a reasonable tendency. In addition, the 95% lower confidence intervals of the proposed and conventional PODs were compared and were almost equal with respect to the decision threshold, indicating the applicability of the proposed method.

Computation of Eigenvalues and Eigenfunctions in the Solution of Eddy Current Problems

The solution of the eigenvalue problem in bounded domains with planar and cylindrical stratification is a necessary preliminary task for the construction of modal solutions to canonical problems with discontinuities. The computation of the complex eigenvalue spectrum must be very accurate since losing or misplacing one of the thereto linked modes will have an important impact on the field solution. The approach followed in a number of previous works is to construct the corresponding transcendental equation and locate its roots in the complex plane using the Newton-Raphson method or Cauchy-integral-based techniques. Nevertheless, this approach is cumbersome, and its numerical stability decreases dramatically with the number of layers. An alternative, approach consists in the numerical evaluation of the matrix eigenvalues for the weak formulation for the respective 1D Sturm-Liouville problem using linear algebra tools. An arbitrary number of layers can thus be easily and robustly treated, with continuous material gradients being a limiting case. Although this approach is often used in high frequency studies involving wave propagation, this is the first time that has been used for the induction problem arising in an eddy current inspection situation. The developed method is implemented in Matlab and is used to deal with the following problems: magnetic material with a hole, a magnetic cylinder, and a magnetic ring. In all the conducted tests, the results are obtained in a very short time, without missing a single eigenvalue.