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Xie S.,Tohoku University | Yamamoto T.,Japan Power Engineering and Inspection Corporation | Takagi T.,Tohoku University | Uchimoto T.,Tohoku University
Studies in Applied Electromagnetics and Mechanics

In nuclear power plants, there may happen local wall-thinning on the inner surface of a pipe due to the flow of coolant flowing inside the pipe. Pulsed eddy current testing (pulsed ECT) technology is developed in recent years. Because of its rich frequency components and applicability of large electric current, a pulsed ECT method may show promising capability of detecting and evaluating the defect in the deep region of the material. The aim of this study is to discuss the feasibility of detection and evaluation of local wall-thinning of the bottom surface in one thick layer and also in the lower layer of two-layer structure pipe using a pulsed ECT method. Concerning the large thickness of the specimen, a high sensitive flux gate (FG) sensor has been employed and the corresponding differential exciting mode has been developed to efficiently apply the FG sensor. Experimental results show that this FG sensor combined with differential exciting mode could detect a very small defect that is located in a thick specimen while which could not be detected by Hall sensor. © 2011 The authors and IOS Press. All rights reserved. Source

A nondestructive testing method is presented for inspection and evaluation of back-side local thinning in ferromagnetic structures. It is shown that the change of initial magnetic leakage reluctivity is correlated with a local thinning's reduced thickness and thinning area; a thinning's transversal length is more significant than the longitudinal length in terms of thinning area. The faint magnetic flux leakage excited from back-side local thinning can be detected by highly sensitive magneto-impedance sensors. Validation tests were carried out by moving a probe over a local thinning in the transversal and longitudinal directions, respectively. Results show the feasibility of inspecting and evaluating back-side local thinning by using small magnetization force and highly sensitive magneto-impedance sensors. © 2001-2012 IEEE. Source

Cheng W.,Japan Power Engineering and Inspection Corporation | Saito Y.,Hosei University
Journal of Applied Physics

B-H loop and its modeling are essential for ferromagnetic material characterization and electromagnetic simulation. The objective of this study was to characterize material change by analyzing the corresponding B-H loops and construct a general B-H model for electromagnetic simulation. A B-H loop was decomposed in terms of either ideal or normal magnetization curves, and the respective curves are single-valued functions of B and dB, which can be constructed using harmonic balance method. The B-H loop analysis and modeling were simplified by the loop decomposition approach. © 2015 AIP Publishing LLC. Source

Inoue M.,University of Toyama | Mihara T.,University of Toyama | Tashiro H.,University of Toyama | Furukawa T.,Japan Power Engineering and Inspection Corporation
Japanese Journal of Applied Physics

Although in previous studies were examined the ultrasonic reflection behaviors at a nano-air gap using a relatively small optical Newton's ring specimen and a commercial acoustic lens, the details of the quantitative ultrasonic behaviors at a nano-air gap have remained unqualified until now. Since the accuracy of estimating these behaviors is directly related to the accuracy of industrial ultrasonic crack sizing, we tried to measure more accurately quantitative ultrasonic behaviors at a nano-air gap in this study. For this purpose, a special highly focused acoustic lens was designed and fabricated and applied to a large optical Newton's ring specimen to obtain accurate and reliable experimental results. Comparisons between the experimental and the conventional small gap theoretical results for a nano-air gap were also carried out. As a result, ultrasonic transmission was found to begin to occur from 60-70nm air gaps in all the measurements. This finding was largely different from that based on the gap theory. Regarding the cause of this large difference between the experimental and theoretical results, we also examined the influence of the surface roughness of contact plates. © 2012 The Japan Society of Applied Physics. Source

Mizuno R.,Japan Power Engineering and Inspection Corporation
International Conference on Nuclear Engineering, Proceedings, ICONE

Temper bead welding is applied as one of repair methods for reactor vessels made of low alloy steel. It is desirable that hardness of the weld heat affected zone in the temper bead weld is less than 350HV to prevent the cold cracking. As diffusible hydrogen in a factor of cold cracking hardly diffuses in austenitic weld metal cold, cracking is available to be prevented. Cold cracking and the mechanical properties of the weld by gas tungsten arc welding using welding material of Ni-based alloy was evaluated. Even if maximum hardness in the weld heat affected zone is more than 400HV, cold cracking don't occur, and also the mechanical properties are good. Copyright © 2015 by JSME. Source

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