Enhancement of Nondestructive Evaluation Technique for Magnetic and Nonmagnetic Structural Components

JNC TN9400 2000-021, 104 Pages, 2000/03

JNC-TN9400-2000-021.pdf:5.21MB

ln this report, research works performed in the Structura1 Safety Engineering Group of OEC/JNC are summarized as the final report of the doctoral fellowship. The main objective of this study is for the enhancement of the nondestructive evaluation techniques for structural components of both magnetic and nonmagnetic material. Studies in three topics have been carried out aiming at the quantitative evaluation of crack with the eddy current testing and the validation of a natural magnetic field based NDE method for detecting mechanical damages in a paramagnetic material. ln the first part of the study, an approach to the reconstruction of the natural crack was proposed and implemented with an idealized crack model for its validation. ln the second part, the correlation of the natural magnetization and the mechanical damages in the SUS304 stainless steel was investigated by using an experimental approach. ln part 3, an inverse method of the measured magnetic fields is proposed for the reconstruction of magnetic charges in the inspected material by using an optimization method and wavalet. As the first work, an approach to the reconstruction of an idealized natural crack of non-vanishing conductivity is proposed with use of signals of eddy current testing. Two numerical models are introduced at first for modeling the natural crack in order to represented it with a set of crack parameters. A method for the rapid prediction of the eddy current testing signals coming from these idealized cracks is given then by extending a knowledge based fast forward solver to the case of a non-vanishing conductivity. Based on this fast forward solver, the inverse algorithm of conjugate gradient method is updated to identify the crack parameters. Several examples are presented finally as a validation of the proposed strategy. The results show that both the two numerical models can give reasonable reconstruction results for signal of low noise. The model concerning the touch of ...

Evaluation of creep-fatigue damage accumulation by means of electrochemical nondestructive detection method

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PNC TJ9601 96-003, 38 Pages, 1996/03

PNC-TJ9601-96-003.pdf:1.87MB

In this study, for the purpose of development of a nondestructive detection technique of creep-fatigue damage in Type 316FR stainless steel for fast reactors, application study of electrochemical methods and the Induced Current Potential Drop(ICFPD) was done. Applicability of electrochemical methods to evaluation of grain boundary precipitates which, provide preferred site for cavities was investigated. Anodic polarization curves were measured both in 1N KOH solution and in 1N HSO+KSCN solution. An anodic current peak that, corresponds to preferential dissolution of the grain boundary precipitates was observed in the measurements using in the KOH solutlon. It was suggested that evolution of the grain boundary precipitates which should be associated with creep-fatigue damage can be evaluated by the electrochemical method using KOH solution. The results of reactivation ratio of the material in 1N HSO+KSCN solution, which is recognized as the sensitive indicator of Cr-depletion, suggested a correlation between the reactivation ratio and creep-fatigue damage. Clear differences between the as-received material and the creep-fatigue damaged sample were found in ICFPD results. Although more detailed investigation is required to make a conclusion, it was expected that potential drop can reflect creep-fatigue damage in the microstructure, e.g. precipitates cavities, surface cracks. Based on the preliminaly result, the ICFPD technique may be expected to provide a quantitative monitoring capability of creep-fatigue damage.