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In situ electrochemical study on crevice environment of stainless steel in high temperature water

高温水中におけるステンレス鋼のすき間環境のその場観察

相馬 康孝; 加藤 千明; 上野 文義

Soma, Yasutaka; Kato, Chiaki; Ueno, Fumiyoshi

高温高圧水中におけるステンレス鋼のすき間内環境を調べるために、電気化学的手法によるその場観察を行った。小型($$phi$$250$$mu$$m)のセンサーをすき間内に設置し、すき間内の局部的導電率、$$kappa$$$$_{rm crev}$$、分極抵抗、および腐食電位の測定を行った。これにより、バルク水導電率、バルク水溶存酸素濃度などの外部環境を変動させた際のすき間内環境の応答挙動をリアルタイムに分析した。その結果、すき間内の場所に依存して$$kappa$$$$_{rm crev}$$が1桁以上変動すること、$$kappa$$$$_{rm crev}$$はバルク水の溶存酸素濃度を脱気状態から30ppb程度までに上昇させただけで敏感に応答して増加すること、溶存酸素濃度32000ppbでは$$kappa$$$$_{crev}$$はバルク水の100倍以上の値となること、並びにそれらの挙動はすき間形状に大きく依存することを明らかとした。

In-situ electrochemical measurement within crevice of stainless steel in 288$$^{circ}$$C water has been conducted to analyze crevice water chemistry. Small sensors ($$phi$$ $$sim$$ 250$$mu$$m) measured local solution electrical conductivity, $$kappa$$$$_{rm crev}$$, polarization resistance, and electrochemical corrosion potential. Real-time response of the $$kappa$$$$_{rm crev}$$ as functions of bulk water conductivity, dissolved oxygen (DO) concentration has been quantitatively analyzed. The effect of geometrical factors on the crevice environment was also studied. The $$kappa$$$$_{rm crev}$$ differ more than an order of magnitude depending on the oxygen potential inside the crevice. The $$kappa$$$$_{rm crev}$$ increased by small amount of bulk DO (e.g. 30 ppb). Maximum $$kappa$$$$_{rm crev}$$ was observed with DO of 32000 ppb and became more than 100 times higher than that of bulk water. Crevice geometry affected significantly on the water chemistry inside.

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