Intergranular corrosion mechanism of ultra-low carbon type 304 stainless steel in a nuclear reprocessing plant

核燃料再処理施設における極低炭素304ステンレス鋼の粒界腐食機構

上野 文義  ; 加藤 千明   ; 本岡 隆文; 市川 史郎*; 山本 正弘 

Ueno, Fumiyoshi; Kato, Chiaki; Motooka, Takafumi; Ichikawa, Shiro*; Yamamoto, Masahiro

本研究は、再処理施設の機器の寿命評価技術開発や腐食機構の解明を目的として、極低炭素ステンレス鋼340ULC製の減圧運転条件の蒸発缶の伝熱管の腐食挙動について検討した。モックアップ試験体を製作して長時間の試験を行った。試験の結果、腐食速度は試験開始から増加するが、約25,000時間を越えると一定に達した。粒界腐食深さを測定した結果、粒界腐食は一つの粒の周囲の粒界すべてを進行した後、溶液中に脱粒しながら進行すると考えられた。

Authors were aimed for development of life evaluation method of components and clarification of corrosion mechanism of the components in nuclear reprocessing plant. Corrosion behavior of heat exchanger tubes in the reduced pressure evaporator made by ultra-low carbon type 304ULC stainless steel was studied. A simplified mock-up test apparatus was used for corrosion test with long-term test duration. Following results were obtained. The corrosion rates were increased from beginning of the test to more than 25,000 hours and then corrosion rate was reached to constant. From the measurement results of intergranular penetration depths, it was thought that intergranular corrosion was progressed on entire grain boundary around a grain and then the grain dropped out to the solution.