Field Eddy Current Probe Research Articles

Radial Field Detector to Improve Sensitivity of Localized Defects in Remote Field Eddy Current Technique

ABSTRACT This paper presents the development of a cone-shaped radial magnetic-field-detector–based remote field eddy current (RFEC) probe for enhanced detection of localized defects in ferritic steel tubes. The performance of the radial coil detector has been evaluated for the detection of different types of defects such as through holes, flat bottom holes and notches of different sizes and orientations. The RFEC signals are observed to be corrupted by heavy noise due to spatial variations in material permeability. To remove the random noise from the nonstationary time series RFEC signals, empirical mode decomposition (EMD) processing has been adopted and has been found to significantly improve the signal-to-noise (SNR) ratio. Furthermore, the effect of the circumferential extent of defects on the signal amplitude is analyzed through experimental and finite-element-model–based studies. The linear resolution of the designed radial coil detector and its repeatability behavior are also scrutinized. Studies demonstrate that the developed radial field detector is a promising configuration in remote field eddy current technique for enhanced defect detection and also in designing an array probe.

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.

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.

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.

A Novel Rotational Field Eddy Current Planar Probe with Two-Circular Sector Pickup Coils.

A new rotational field planar eddy current probe is proposed. The probe is combined with two orthogonal driver traces and a pickup coil that includes two-circular sector windings with series connection. Rotational eddy currents are induced by driver traces of the same amplitude and frequency, but fed with 90° phase different alternating exciting currents. An experimental demonstration using prototypes of the probes and artificial defects showed that the probe with a two-circular sector pickup coil is more sensitive for detecting the short defects than the probe with a circular pickup coil.

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

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

Defect detection in stainless steel tubes with AMR and GMR sensors using remote field eddy current inspection

The purpose of this paper is to compare the performance of the giant magneto-resistor (GMR) and anisotropic magneto-resistor (AMR) sensors for remote field eddy current testing in stainless steel tubes. Two remote field eddy current probes were built to compare detection and characterization capabilities in standard defects like longitudinal and transverse defects. Both probes include a coil to produce a sinusoidal magnetic field that penetrates the tube wall. Each probe includes a detector with GMR and AMR sensors, where each sensor has four magneto-resistive elements configured in a Wheatstone bridge. Each sensor needs to be biased differently to operate in the high sensitivity linear mode. The description of the measurement system used to detect defects is present in the paper. For the choice of the detector optimal position, numerical simulation and experimental measurements were performed. For comparison of these sensors in defect detection using remote field eddy current testing, the experimental measurements were performed under the same conditions. The results are presented and discussed in the paper.

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

Rotating field eddy current probe with bobbin pickup coil for steam generator tubes inspection

Eddy current probes are used extensively to evaluate the integrity of steam generator tubes in nuclear power plants and to detect cracks in tube walls. The probe design has evolved from simple bobbin probes to mechanically rotating multi-coil probes providing high resolution images of tube integrity. This paper presents a novel rotating field eddy current probe with bobbin pickup coil that generates a rotating magnetic field, thereby avoiding mechanical rotation of probe. Three balanced identical rectangular windings carrying excitation currents with 120° phase difference generate an electrically rotating magnetic field that is sensitive to defects of all orientations. A bobbin coil located in the center is used as a pick up sensor. The phase of induced voltage in the bobbin coil is interpreted in terms of the circumferential location of the defect. The properties of the probe are investigated using a three dimensional finite element model, and validated experimentally using measurements.

3D RFEC simulations for the in-service inspection of steam generator tubes in fast breeder reactors

Three-dimensional numeric simulations, based on the finite element model, are conducted to simulate the In-Service Inspection of magnetic steam generator tubes of a Fast Breeder Reactor using remote field eddy current probes. The influen ce of sodium in the gap SP-tube and outer defect detectability is computed for a large SP model with multiple SG tubes using the 3D-RFECT code.

Application of a superconductor to the shield of a remote field eddy current testing probe

Application of a superconductor to the shield of a remote field eddy current testing 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>