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Investigation of the on-line monitoring sensor for a pipe wall thinning with high accuracy

高精度配管減肉オンラインモニタリングセンサの研究

田川 明広; 藤木 一成; 山下 卓哉

Tagawa, Akihiro; Fujiki, Kazunari; Yamashita, Takuya

日本の原子力発電所では、時間基準保全から状態基準保全に移行しつつある。しかし、配管減肉に限定したとき、オンラインモニタリング可能なセンサはなかった。そこで、電磁超音波探触子(EMAT)を用いた、200$$^{circ}$$Cの高温環境下で接触媒質を用いずにオンラインモニタリング可能であるセンサを開発した。減肉の測定方法は、超音波の受信間隔から板厚を測定するパルスエコー法(PE法)と共鳴周波数から板厚を求める電磁超音波共鳴法(EMAR)を用いた。開発したセンサは200$$^{circ}$$Cの環境で、EMARで2mm$$pm$$0.01mm、PE法で5mm$$pm$$0.04mmの厚さが測定可能であった。また、磁石の初期減磁による影響を考慮できる200時間の耐久性を有することも確認した。

In Japan, the safety of nuclear power plants has been secured by performing a time-based maintenance. However recently, NPPs were taking into consideration a new procedure using a condition-based maintenance, aiming to improve both reactors safety and operation availability. Therefore, it is needed to develop new sensors that can monitor, during reactor operation, the integrity of both piping system and pressure vessel. Also, a proper measurement method has to be chosen in order to carry out an effective on-line monitoring. In the present investigation, it was used the electromagnetic acoustic transducer (EMAT) because it does not need a couplant in a high-temperature environment (up to 200 $$^{circ}$$C). Based on this method, two measurements techniques have been employed using a new developed sensor, depending on the required purpose. The 1st technique is based on the Pulse Echo (PE) method. The paper analyses different methods for carrying out plates thickness measurement using EMAT and supplying a vertical ultrasonic wave. The 2nd technique is based on the electromagnetic acoustic resonance (EMAR) that is usually used for material fatigue assessment. The developed sensor measures, at 200 $$^{circ}$$C, a minimum 5 mm (0.04 mm) plate thickness using PE, and 2 mm (0.01 mm) using EMAR, respectively. Moreover, it was found no attenuation of the sensor signal even when the sensor performed a 200 hours continuously measurement.

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