Bobbin Probe Research Articles

Modeling and investigation of crack evaluation in metal tube based on magnetic field analysis method

In this paper, an analytical model of eddy current testing of a metal tube has been proposed to evaluate circumferential cracks from the signals of the magnetic field. First, based on Maxwell’s equations in time-harmonic form, magnetic vector potential equations for each region of space are built under two different configurations of the bobbin probe and the encircling probe respectively. Next, the magnetic vector potentials are solved by imposing conditions at the interface. Then, series expressions of the radical and axial magnetic induction intensities have been obtained. In addition, based on the proposed modeling, the influences of cracks at different locations on the surface magnetic field have been analyzed. The results have shown that the radial magnetic induction intensity increases while the axial magnetic induction intensity decreases for the internal and external cracks with the same shape and size on the surface of the metal tube. Moreover, the magnetic induction intensity has shown much more sensitive property to external cracks than it has done to internal cracks for the encircling probe. However, for the bobbin probe, the magnetic induction intensity has demonstrated almost the same sensitivity in detection for both internal and external cracks in the metal tube. The researching results have important theoretical and practical significance for understanding the physical process of eddy current testing, optimizing parameters of the experimental system and building the inversion model.

Simulation and experimental study on ECT of circumferential cracks in small-diameter tubes

Circumferential crack detection of small diameter tubes is a difficult problem to solve in eddy current testing. The three-dimensional simulation model is established through electromagnetic field simulation software to analyze the eddy current field distribution of the traditional bobbin probe and transverse cylindrical probe in small diameter tubes. The results show that the circumferential crack has a more marked disturbance to the eddy current field generated by the latter. Based on the simulation research, a new type of probe based on transverse excitation is designed to detect the artificial circumferential crack of the specimen with the designed probe, which can effectively detect the circumferential crack and has a potentially high sensitivity to the narrower natural circumferential crack.

A novel circumferential eccentric eddy current probe and its application for defect detection of small-diameter tubes

When it comes to the detection of defects in small-diameter tube, eddy current testing (ECT) using Bobbin probe is the traditional method. Although this way is quite efficient, it is not available to obtain the circumferential information of the defect due to its inherent disadvantage. In this study, a novel probe has been proposed which can obtain both axial and circumferential information of defects, still with high efficiency. During testing, the probe carries out axial scan for defect searching in axial direction, and when defect is discovered, the circumferential eccentric rotating scan module will be executed. Thus, this novel probe can achieve multiple defect information with high efficiency. The specific research contents are as follows. Firstly, the eccentric and rotatable EC probe is designed suitably for small-diameter tubes, with the simulation model built up for signal analysis. Then, the feasibility of this novel probe is verified by integrating the obtained simulation data, showing the advantages of the developed probe for obtaining both axial and circumferential multiple information of defects in small-diameter tube. Finally, the novel probe is fabricated, and the testing system is established. The corresponding experiments are conducted, certifying the superiority and efficiency of the new type of probe further.

Analysis of Eddy-Current Probe Signals in Steam Generator U-Bend Tubes Using the Finite Element Method

To ensure the integrity and safety of steam generator tubes in nuclear power plants, eddy-current testing is periodically employed. Because steam generators are equipped with thousands of thin-walled tubes, the eddy current is tested using a bobbin probe that can be used at high speed. Steam generator heat pipes in nuclear power plants have different sizes and shapes depending on their row number. In particular, heat pipes in the first row are located inside the steam generator and are of the U-bend type because the radius of the curved pipe is the smallest. A steam generator heat pipe has a thickness of about 1 mm, so a geometrical cross-sectional area change may occur due to residual stress when manufacturing the curved pipe. It is difficult to determine an exact shape because the change in cross-sectional area generated during the manufacturing process varies depending on the position of the pipe and the distortion rate. During eddy-current testing (ECT), to ensure the integrity and safety of the steam generator tubes, the shape change of the bend may cause a noise signal, making it difficult to evaluate defects in the pipe. However, the noise signals generated in this situation are difficult to analyze in a real measurement environment, and difficult to verify by producing a mock-up, which complicates distinguishing a noise signal from a defective signal. To solve this problem, various noise signals were obtained using the electromagnetic analysis method of COMSOL Multiphysics, a commercial program based on numerical analysis of the finite element method, to simulate the environment, including the change in cross-sectional area of the heat pipe. When compared to the actual measurement signal, the accuracy of the simulations improved, and various types of noise signals were detected, which may be helpful for accurate evaluations of defects during actual inspections.

Flaw Classification Algorithm for Heat Exchanger Tubes Using a Bobbin-Type Magnetic Camera

This paper presents an algorithm that estimates the presence, location, shape, and depth of flaws using a bobbin-type magnetic camera consisting of bobbin probes and a bobbin-type integrated giant magnetoresistance (GMR) sensor array (BIGiS). The presence of the flaws is determined by the lobe path of the Lissajous curves obtained from bobbin coil with respect to the applied frequency. The location of the flaw, i.e., whether it is an inner diameter (ID) or outer diameter (OD) flaw, can be determined from the rotational direction of the lobe with respect to the frequency change. The shape of the flaw is then determined from the area of the lobe and the BIGiS image. At this stage, multi-site damage can be determined from the BIGiS image. The effectiveness of the flaw classification algorithm was evaluated using various types of artificial flaws introduced into small-bore tube test specimens made of austenitic stainless steel.

Novel eddy current probes for pipes: Application in austenitic round-in-square profiles of ITER

Novel eddy current probes were developed to detect sub-millimetre defects with any orientation on the inner surface of pipes. Five different probes were designed, produced and experimentally validated. These probes include arrays of planar trapezoidal coils in a flexible substrate used alone or together with different winded drive coils. Numerical simulations with Finite Element Method were used to predict the probe response to defects with any orientation. Experimental results in austenitic steel jackets used in ITER revealed that the new probes have an improved reliability compared to conventional toroidal bobbin probes, allowing a higher sensitivity to circumferential defects.

이물질에 대한 ECT Bobbin Probe 검출 감도

이물질에 대한 ECT Bobbin Probe 검출 감도

A prediction method for the general corrosion behavior of Alloy 690 steam generator tube using eddy current testing

The purpose of this work is to develop an eddy current testing method to predict the general corrosion behavior of Alloy 690 steam generator tubes. A corrosion test was conducted for tubes with different levels of eddy current noise in simulated primary water at 330°C, and their corrosion behavior was correlated with the tube noise measured using bobbin and rotating probes. The corrosion behavior was closely correlated with the tube noise measured using a rotating probe. However, there was no correlation between the corrosion behavior and the tube noise measured using a bobbin probe. The tube noise value measured using a rotating pancake coil probe is suggested to be a significant parameter in estimating the general corrosion behavior of tubes.

Simulation and design of ECT differential bobbin probes for the inspection of cracks in bolts

All Various defects could be generated in bolts for a use of oil filters for the manufacturing process and then may affect to the safety and quality in bolts. Also, fine defects may be imbedded in oil filter system during multiple forging manufacturing processes. So it is very important that such defects be investigated and screened during the multiple manufacturing processes. Therefore, in order effectively to evaluate the fine defects, the design parameters for bobbin-types were selected under a finite element method (FEM) simulations and Eddy current testing (ECT). Especially the FEM simulations were performed to make characterization in the crack detection of the bolts and the parameters such as number of turns of the coil, the coil size and applied frequency were calculated based on the simulation results.

Development of probability of detection functions for evaluating integrity of axial outside diameter stress corrosion cracks in steam generator

The reliability of an eddy current testing (ECT) inspection system depends upon the inspection technique and quality of analyst. In evaluating the integrity of a steam generator (SG) tube, degradation detection and sizing accuracy are considered performance measures of the nondestructive evaluation (NDE) system. A probability of detection (POD) model serves as a functional measure of the ability of an NDE system to detect degradation. It is one of the inputs in the operational assessment, and it is used to estimate the degradation during service via ECT of the SG tube. In this study, the POD functions of the inspection technique and analyst were obtained to quantitatively analyze the ECT bobbin probe for axial outside diameter stress corrosion cracks in SG tubes. This should serve to evaluate the integrity of the SG tubes. The depth and amplitude of defects were used as parameters of the POD model. Hit (detection) and miss (no detection) binary data obtained from destructive and nondestructive inspection of cracked tubes were also used.

Eddy Current Testing Probe to Improve the Defect Detection Sensitivity of Metal Tube

The structure of conventional bobbin probe was modified to improve the detection sensitivity of defects in metal tube. Based on the results of finite element simulation, several types of modified probes are fabricated and used to detect artificial defects in tube and the defect signals are acquired and analyzed. The simulation and experimental results verified that the modified eddy current probes are more sensitive to non-axial defects than conventional bobbin probe and can improve the reliability of tube inspection.

Automated Analysis Technique Developed for Detection of ODSCC on the Tubes of OPR1000 Steam Generator

A steam generator (SG) tube is an important component of a nuclear power plant (NPP). It works as a pressure boundary between the primary and secondary systems. The integrity of a SG tube can be assessed by an eddy current test every outage. The eddy current technique(adopting a bobbin probe) is currently the main technique used to assess the integrity of the tubing of a steam generator. An eddy current signal analyst for steam generator tubes continuously analyzes data over a given period of time. However, there are possibilities that the analyst conducting the test may get tired and cause mistakes, such as: missing indications or not being able to separate a true defect signal from one that is more complicated. This error could lead to confusion and an improper interpretation of the signal analysis. In order to avoid these possibilities, many countries of opted for automated analyses. Axial ODSCC (outside diameter stress corrosion cracking) defects on the tubes of OPR1000 steam generators have been found on the tube that are in contract with tube support plates. In this study, automated analysis software called CDS (computer data screening) made by Zetec was used. This paper will discuss the results of introducing an automated analysis system for an axial ODSCC on the tubes of an OPR1000 steam generator.

The influence of a bobbin probe's radial offset on eddy current testing of tubes

The influence of a bobbin probe's radial offset on eddy current testing of tubes

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.

Eddy current probes of inclined coils for increased detectability of circumferential cracks in tubing

Conventional bobbin probes, multi-pancake and/or rotating pancake probes, and transmit-receive probes for eddy current tests (ECTs) are currently used to test metal tubing. Each method has its respective strengths and weaknesses considering their characteristics such as test speed, flaw detection sensitivity, and probe structure complexity. This paper proposes a novel eddy current probe with new features. The structure is designed to be sensitive to circumferential cracks, which are not easily detected using conventional bobbin coil probes, as well as longitudinal cracks. The directions of the eddy current around the coils were designed to be not circumferential. The ECT signals of these probes were acquired and analyzed from the artificial defects manufactured for this study. The experimental results show that the proposed probes are more sensitive to circumferential defects than the comparable conventional bobbin probes. In addition, the proposed probes are also sensitive to axial defects. By employing both the new probes and the conventional bobbin probes, ECTs for the metal tubing can be performed more reliably.

원전 증기발생기 전열관 와전류검사용 보빈코일의 권선 수 변화에 대한 전기적 특성 연구

Two kinds of eddy current probes are mainly used to perform the steam generator tube integrity assesment in NPPs. The first one is the bobbin probe using for inspection of volumetric defect like a fretting wear. The second one is the rotating probe using for inspection of non-volumetric defect like a crack. The eddy current probe is one of the essential components which consist of the whole eddy current examination system, and provides a decisive data for the tube integrity in accordance with acceptance criteria described in specific procedures. The design of ECT probe is especially important to improve examination results because the quality of acquired ECT data is depended on the probe design characteristics, such as coil geometry, electrical properties, operation frequency. In this study, it is analyzed that the coil winding number of differential bobbin probe affects the electrical properties of the probe. Eddy current bobbin probes for the steam generator tubes in NPPs are designed and fabricated according to the results. Experiment shows that the change in coil winding number has much effects on the optimum inspection frequency determined by the tube geometry and material. Therefore, the coil winding number in bobbin probe is very important in the probe design. In this study, a basis of the coil winding number for the eddy current bobbin probe design for steam generator tubes in NPPs is established.

Development of Magnetic Phase Detection Sensor for the Steam Generator Tube in Nuclear Power Plants

A new eddy current testing probe was developed to separate the eddy current signal distortion caused by permeability variation clusters and ordinary defects created in steam generator tubes. Signal processing circuits were inserted into the probe to increase the signal-to-noise ratio and allow digital signal transmission. The new probe could measure and separate the magnetic phases created in the steam generator tubes in the operating environment of a nuclear power plant. Furthermore, the new eddy current testing probe can measure the defects in steam generator tubes as rapidly as a bobbin probe with enhanced testing speed and reliability of defect detection.

OPTIMIZED DESIGN PARAMETERS OF EDDY CURRENT BOBBIN PROBE FOR STEAM GENERATOR TUBE IN NPPS

The bobbin probe is now widely accepted as a basic and important ECT technique among various ECT techniques for steam generator tube integrity assessment that is practiced during each plant outage. The bobbin probe is also one of the essential components which consist of the whole ECT examination system, and provides us with decisive data for the evaluation of tube integrity in accordance with acceptance criteria described in specific procedures. Accordingly, the design of ECT probe is especially important to examination results because the quality of acquired ECT data is determined by the optimized probe design characteristics, such as coil geometry, electrical properties, operation frequency, and so on. In this study, the relationship between electric characteristic changes and differential coil gap variation for the optimization of the ECT probe signal was investigated. As a result, for the examination of volumetric flaws fabricated on the O.D. side of ASME type calibration standard, we propose that the best Lissajous signal for the examination will be obtained when the coil gap of differential bobbin probe is approximately 1.2 ~ 1.6 mm .

Multi-Coil Eddy Current Probe for the Detection of Circumferential Cracks in Tubing

Conventional eddy current bobbin probes, multi-pancake and/or rotating pancake probes, and transmit-receive eddy current probes are currently utilized in testing metal tubing. Each method has respective strengths and weaknesses. This paper proposes another eddy current probe with new features. The structure is designed to be sensitive to circumferential cracks, which are not easily detected with ordinary bobbin coil probes. The directions of the magnetic field and the eddy current around the coil were considered in design of the probe structure. Signals of these probes from the artificial defects were acquired and analyzed. Experimental results show that the developed probes are more sensitive to circumferential defects than comparable ordinary bobbin probes. In addition, the new probes are insensitive to axial defects. By employing both the new probes and ordinary bobbin probes, more reliable ECT can be performed.

Numerical Analysis of Compound ECT Signals due to Various Tube Defects near Support Plate in Steam Generator

In this paper, eddy current signals from various anomalous defects in the steam generator tube are numerically predicted and their signal slope characteristics are investigated. The signal variations due to increased frequencies are also observed. Based on the accumulated knowledge, the analysis of compound signal is attempted which includes the effect of support plate. Both differential and absolute bobbin probe signals are analyzed. For the signal prediction, axisymmetric finite element modeling is used and this leads us to the utilization of slope angle analysis of the signal. Results show that differential signals are useful for locating the position of defect under the support plate, while absolute signals are easy to presume and interpret even though the effect of support plate is mixed. Combined use of these two types of signals will help us accomplish a more reliable inspection.