This paper introduces the application of electrochemical measurement system to the maintenance management in chemical plant. In the application of this measurement system, it needs the construction of the maintenance management system and the confirmation of the level of measurement accuracy to apply the system. In the construction of the maintenance management system, it is required to clarify what kind of information is needed. In the confirmation of the level of measurement accuracy, it is necessary the level of measurement accuracy and the correspondence to the required information for maintenance management.
The near-ground boundary of an embedded steel member is especially vulnerable to corrosion, which can be caused by long-term exposure to stagnant rainwater or other environmental factors. Many cases of fracturing due to progressive local corrosion have been reported. This study undertakes a fundamental examination of the output properties and practicality of a corrosion sensor devised by the authors to evaluate the corrosion resistance of steel members near the ground. The output characteristics of this sensor were investigated by simulating NaCl aqueous solution environments, including the atmosphere-liquid interface. In addition, an indoor exposure test was also conducted using uncoated steel plates in the same aqueous solution. The actual corrosion depths obtained from the exposure test were compared with the estimated corrosion depths according to sensor measurements. Moreover, an evaluation method using the corrosion sensor has been proposed for the prediction of the time-dependent corrosion depth of steel members.
Dose-response functions （DRFs） are examined in terms of applicability to the data of outdoor exposure tests in Japan （JWTC data） in order to improve estimation methods of assessing the domestic atmospheric corrosivity of carbon steel and zinc. From literature survey, the ISO9223DRF is selected as a suitable DRF. Estimated corrosion rate by the ISO9223DRF shows insufficient agreement with the measured one from the JWTC data. The coefficients of the ISO9223DRF are redetermined by a nonlinear least-squares regression model based on the JWTC data （fitted DRF）. Estimated corrosion rate by the fitted DRF shows better agreement with the measured one from the JWTC data in terms of correlation with the measured one and fraction of the estimated one within errors of －50～＋100％.
This research was conducted with the objective of developing knowledge on the integrity evaluation of carbon steel in the primary containment vessel at the time of taking out fuel debris at the Fukushima Daiichi Nuclear Power Station （1F） of TEPCO Holdings Corporation. The effect of borate administration on the self-passivation behavior of carbon steel was evaluated based on the time course of the natural corrosion potential in the natural immersion test, and the analysis results of water before and after the test. From the results, a method to estimate the self-passivation tendency by the carbon steel self-passivation index（SPI）
was presented. Here, [B（OH）4－]E was obtained as B（OH）4－-equivalent by the following formula.
That is, the self-passivation tendency of carbon steel in a reactor containment vessel in a borate-containing solution environment may be estimated by sodium pentaborate dosage concentration, M-alkalinity, sulfate ion concentration, chloride ion concentration and bicarbonate ion concentration. According to this technique, when the SPI is less than 0.282, carbon steel self-passivates.