室温での炭素鋼の腐食に及ぼす純水中の微量不純物の影響

抄録

Corrosion behavior of carbon steel, as affected by trace impurities in pure water (specific conductivity below 10μS/cm), was evaluated at room temperature. Impurities were added as sodium or magnesium compounds. Test water conditions were chosen to correspond to those of BWR primary coolant. The results indicated:
1) Corrosion was not promoted by addition of impurities in deaerated water containing oxygen below 5ppb. 2) Carbon steel was passivated in pure water (specific conductivity=0.06μS/cm) containing oxygen above 40ppb, however this state was unstable and corrosion was promoted by trace amounts of anions, prohibiting the passivity of steel. 3) The addition of anionic HPO₄^2- and OH^- did not promote corrosion, since the solution pH became more basic and carbon steel was easily passivated. However, some anions in neutral pH water containing oxygen adsorbed easily on the metal surface and prohibited the passivity of steel, thus lowering the corrosion potential and promoting corrosion. The ability to prohibit passivity decreased in the order SO₄^2->Cl^->NO₃^-. 4) Dissolved oxygen, at concentrations not high enough to inhibit corrosion promoted by anions, was found to accelerate corrosion.