Influence of sulfide concentration on the corrosion behavior of pure copper in synthetic seawater

人工海水中における純銅の腐食挙動に及ぼす硫化物の影響

谷口 直樹 ; 川崎 学*

Taniguchi, Naoki; Kawasaki, Manabu*

硫化ナトリウムを含む人工海水中において、浸漬試験と低歪速度(SSRT)試験より腐食速度と応力腐食割れ(SCC)挙動を調べた。730日までの浸漬試験の結果、純銅の腐食速度は硫化物濃度に強く依存し、0.001M-NaSでは0.6m/y以下、0.005M-NaSでは2-4m/y、0.1M-NaSでは10-15m/yの値が見積もられた。SSRT試験の結果、明瞭なSCCは硫化物濃度が0.005Mを超える比較的高い濃度条件で認められた。これらの試験結果から、銅は硫化物濃度が0.001Mの低い環境では腐食速度が低く応力腐食割れを起こさないため優れた耐食性を示す可能性がある。硫化物のベントナイト中における拡散を仮定してオーバーパック表面へのフラックスから長期的な銅オーバーパックの腐食量の推定を行い、硫化物濃度と腐食寿命の関係を評価した。

Corrosion rate and stress corrosion cracking (SCC) behavior of pure copper under anaerobic condition were studied by immersion test and slow strain rate technique (SSRT) test in synthetic seawater containing NaS. As the results of the immersion test up to 730 days, the corrosion rate of pure copper was strongly depended on sulfide concentration and was estimated to be less than 0.6 m/y for 0.001M-NaS, 2-4 m/y for 0.005M-NaS and 10-15 m/y for 0.1M-NaS. The results of SSRT test showed that obvious SCC occurred in relatively high sulfide concentration over 0.005M. According to these test results, copper is possible to exhibit superior corrosion resistance in low sulfide concentration of less than 0.001M because of very low corrosion rate and no SCC. The long term corrosion depth due to sulfide was estimated from the sulfide flux to the overpack surface assuming the diffusion of sulfide through bentonite, and the overpack lifetime was evaluated as a function of sulfide concentration in groundwater.