Remote Field Eddy Current Probe Research Articles

Investigation on magnetic shield thickness of remote field eddy current probes for inspection of ferromagnetic and non-ferromagnetic plates

Since Remote field eddy current (RFEC) detection technology is barely limited by the skin effect, it can realize the defect detection of large-thickness components. Whereas, the structure of the RFEC probe for the planar conductor is complicated, resulting in an oversized probe. This hinders the application and development of the RFEC testing technology. In this paper, finite element simulations and experimental verification are used to optimize the RFEC probe structure for flat conductors. The results have shown that the thickness of the magnetic shield is the dominant factor in achieving high performance of RFEC inspection of flat conductors. When inspecting both ferromagnetic and non-ferromagnetic flat conductors, cylindrical magnetic shields with appropriate thickness and appropriate excitation frequencies are preferred for improvement of RFEC testing.

Finite element study of remote field eddy current methods for inner diameter and outer diameter pipeline defect classification

Remote field eddy current (RFEC) methods are widely applied for detecting pipeline defects. However, current RFEC methods cannot distinguish inner diameter (ID) defects from outer diameter (OD) defects. In addition, existing RFEC probes are usually driven by an extremely low-frequency signal, which reduces the detection efficiency. To address these issues, a novel external RFEC probe is designed to improve the detection performance. First, the probe structure is designed using a simulation tool. Second, the excitation and structural parameters are optimally selected. Finally, the relationships between the signal features and the defect dimensions are analysed. The results show that the probe can realise the RFEC effect without shield cages, the exciting frequency is significantly improved and the phase angle can be used to classify ID and OD defects.

Study on Remote Field Eddy Current Testing Technology for Crack-like Defects in Long Truss Structure of Aircraft.

Detection of hidden defects of aircraft long truss structures (aluminum alloy) is a challenging problem. The shape of the aircraft truss structure is complex, and the crack defects are buried in a large depth. Without the restriction of skin effect, remote field eddy current (RFEC) has great advantages in detecting buried depth defects. In this paper, in order to detect the hidden defects of the aluminum alloy aircraft long truss structure, the remote field eddy current probe is improved from two aspects of magnetic field enhancement and near-field signal suppression using the finite element method. The results show that indirect coupling energy is greatly enhanced when the connected magnetic circuit is added to the excitation coil. By adding a composite shielding structure outside the excitation coil and the detection coil, respectively, the direct coupling energy is effectively restrained. As a result, the size of the probe is reduced. By optimizing the coil spacing and probe placement position, the detection sensitivity of the probe is improved. The simulation is verified by experiments, and the experimental results are consistent with the simulation conclusions.

Comprehensive study on radial coil influence in designing segmented remote field eddy current probe for defect detection in ferromagnetic tubes

ABSTRACT In the present study, two types of receiver coils, viz axial and radial type receivers, in the Remote field eddy current technique are considered to detect defects in ferromagnetic tubes. The appropriate distance between the exciter and the receiver coils and the excitation frequency are estimated using the finite element model and validated experimentally. Model-assisted probability of detection studies are performed to examine the capability of radial and axial type receiver coils. Experimental studies on various artificial defects reveal the excellent performance of the radial type receiver coil in terms of the higher number of defect detections, sensitivity and imaging. This paper provides a comprehensive study on radial and axial type receiver coils for developing array probes. Radial coil performs better and also preserves localisation of defect, which is more desirable for developing array probe.

Optimisation of helical geometry of inspection probe for steam generator tubes of the PFBR

The steam generator (SG) tubes of the prototype fast breeder reactor (PFBR) located in Kalpakkam, India, need to be periodically inspected using the remote field eddy current (RFEC) technique. During the pre-service inspection of the SG tubes, it was found that the RFEC probes experienced frequent mechanical breakages. To avoid these failures, changes in the existing structural design of the RFEC probe were required. A helical groove design was proposed to obtain a smooth transition in the variation of stress across the probe during the inspection. It was difficult to calculate the flexural stiffness of the proposed helical geometry probe due to the varying cross-section along its length. In this paper, the smearing approach adopted to calculate the stiffness of the RFEC probe and the sensitivity analysis carried out to determine the optimal design of the probe are discussed. A probe was fabricated based on the helical groove design and tested to qualify its suitability for the SG inspection. The RFEC probe with helical grooves was employed for the pre-service inspection of the SG tubes of the PFBR. More than 200 tubes have been inspected using the proposed design and no mechanical failure of the probe has been observed.

Receiver Signal Analysis on Geometry and Excitation Parameters of Remote Field Eddy Current Probe

The traditional remote field eddy current (RFEC) testing is a method widely applied for detecting the corrosion and wall thinning in a ferromagnetic pipe system and shows intrinsic deficiencies in axial defects quantification due to the distinct probe structure. A circumferential alignment probe structure is used to improve the sensitivity to axial defects of pipes. Meanwhile, current approaches typically are incapable of classifying inner diameter (ID) and outer diameter (OD) defects of the pipe, which brings difficulties to the formulation of strategies in pipe repair. In this article, an external pulsed RFEC method is proposed to address these issues. First, we give a thorough analysis of the effects of probe geometry and excitation parameters on the output signal, targeting parameters optimization. Second, the finite-element model is built and used to analyze the relationships between the defect size and signal features under different excitation types. Finally, the improvements in probe performance and the ability to classify ID and OD defects are validated by measuring the defect depths of the pipe. Results showed that the zero-crossing time feature can be used to distinguish ID from OD defects. Thus, the proposed method is an effective complementary measure for the existing RFEC tools.

Optimal design of remote field eddy current testing probe for ferromagnetic pipeline inspection

Remote field eddy current (RFEC) nondestructive testing has its unique advantages in defect detection of metal pipelines, such as being unaffected by skin effect and material properties, but the size of RFEC probe is large and the signal received by the detection coil is weak. In this paper, a shielding plate is introduced between excitation and detection coil, and a ferromagnetic ring is introduced outside the ferromagnetic pipeline. Both theoretical analysis and finite element method (FEM) simulation are carried out. The result of FEM simulation shows that the distance between the excitation and the detection coil can be shortened after adding a shielding plate; particularly, setting a 1 mm-thick shielding plate 5 mm away from the excitation coil has an optimum optimization effect, which could shorten the distance between the excitation coil and the detection coil by 2 times. The ferromagnetic ring can strengthen the detected signal, and the closer it gets to the detection coil, the stronger magnetic flux density will be detected in the latter. Therefore, it provides a direction for the structural optimization of RFEC testing device.

Defect Detection of Oil and Gas Pipeline using Remote Field Eddy Current Technology

To solve the problem of wall thickness reduction and defects of oil and gas pipeline caused by corrosion or erosion, a remote field eddy current (RFEC) testing method with coaxial double coil structure is proposed to detect corrosion residual wall thickness of oil and gas gathering pipelines. Based on electromagnetic field theories, RFEC technology is theoretically analyzed. The theoretical model of RFEC detection for coaxial double coil structure is established. The relationship between the voltage phase of detection signal and the wall thickness of pipeline is derived, and an evaluation method of the residual wall thickness of the pipeline based on the phase trough time of the RFEC detection signal is proposed. The parameters of RFEC probe are optimized by Finite Element Method, and the detection system is designed on the basis of it. The practicability and the correctness of the theoretical model of the detection system are verified by experiments. It can be used to detect the residual wall thickness of pipelines in real time under different media conditions.

A remote field eddy current probe for outside inspection of pipe defects

A remote field eddy current probe for outside inspection of pipe defects

Development of a High-Sensitive Dual Frequency Remote Field Eddy Current Instrument for Inspection of Ferromagnetic Steam Generator Tubes

ABSTRACTThis paper presents the development of a high-sensitive remote field eddy current (RFEC) instrument for detection of flaws in ferromagnetic steel tubes. The instrument is capable of simultaneously driving the exciter coil of the RFEC probe with two different frequencies and measuring the phase lag of the receiver coil using software-implemented lock-in amplifier. The performance of this high-sensitive RFEC instrument has been demonstrated by detecting a variety of localised flaws in a modified 9Cr–1Mo steel tube used in steam generators. The instrument is sensitive to detect localised flaws of depth, 20% of the wall thickness of 17.2-mm diameter, 2.3-mm thick ferromagnetic steel tubes.

3-D Simulation of Remote Field Eddy Current Detection for Stress Corrosion Cracks in Pipeline

Three-dimensional (3-D)finite element simulation models are conducted to simulate the in-serviceinspection of the axial stress corrosion cracking (SCC) in ferromagneticpipeline using remote field eddy current (RFEC) probes. In this paper, atypical remote field eddy current probe which is internal to and coaxial withthe pipe is firstly introduced. Then a 3-D finite element simulation model isestablished in ANSYS to analyze the detection of RFEC technology. Finally theRFEC signals are observed when changing the geometric parameters, and thedefinite influences of crack size on the amplitude and phase lag of REFCsignals are evaluated. The results of the investigations are beneficial to thedetection and sizing of SCC in pipelines

Performance Estimation of a Remote Field Eddy Current Method for the Inspection of Water Distribution Pipes

Remote Field Eddy Current (RFEC) technology allows the in situ inspection of metallic water distribution pipes. RFEC tools provide the location and magnitude of corrosion defects on the inspected pipes. The capacity of an RFEC tool to detect corrosion defects is evaluated in this paper by comparing its results with those obtained from the analysis of computed tomography (CT) scan images of the inspected pipes. Localization and characteristics of defects identified with the RFEC tool and from the CT scan images were compared for six cast iron pipes. An original method is proposed for the analysis of the CT scan images from which wall thickness losses were estimated by using the basic principle that the attenuation coefficient of X-rays in a homogenous material is a linear function of its density. The results show that the RFEC tool is able to localize most of the defects identified from the analysis of CT scan images. These findings reveal that the tested RFEC probe provided reliable information on the main corrosion defects, and thus on the general structural integrity of the inspected pipes.

Remote field eddy current technique applied to non-magnetic steam generator tubes

Unlike the impedance plane analysis form of common eddy current testing (ECT), the remote field eddy current (RFEC) technique is a through-transmission effect that reduces problems such as lift-off normally associated with ECT. In the inspection of steam generator (SG) tubes, the real issue is to detect the minute cracks growing up from the outside. However, using ECT, it is considered infeasible to accurately find them from the inside because of the limitations of penetration of eddy currents. This paper describes a finite-element approach to the solution of time-harmonic electromagnetic fields for the RFEC technique based on a magnetic vector potential and an electric scalar potential. A comparison is made of experimental and finite-element predictions of electromagnetic phenomena under the inspection of non-magnetic tubes. For the cracks outside demanding high sensitive and precise measurements in the SG tube inspection, numerical results are given for parameters to design a RFEC probe.

Design of remote field eddy current probe for gas pipes (In Japanese: English Abstract) : Kikuta, T.; Yamagishi, T.; Hosohara, Y.; Yamada, I. Journal of JSNDI, Vol. 41, No. 2, pp. 81–89 (Feb. 1992)

Design of remote field eddy current probe for gas pipes (In Japanese: English Abstract) : Kikuta, T.; Yamagishi, T.; Hosohara, Y.; Yamada, I. Journal of JSNDI, Vol. 41, No. 2, pp. 81–89 (Feb. 1992)

Pulsed RFEC probe response

A finite element/finite difference algorithm is described for modeling the pulsed excitation of a remote field eddy current (RFEC) probe used in steel pipeline inspection. Previous work has largely been concerned with the steady-state AC operation of the probe and physical explanations, based on finite element studies, of the probe's sensitivity to outer wall defects. In the present work, the authors discuss the probe response to a sinusoidal pulse and show that such an excitation mode can also be used for outer wall defect detection.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>