Effect of Dissolved Oxygen on Corrosion Inhibition of Cr-Mo Steel Using Sodium Nitrite

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  • Miura Kenzo
    Tamano Laboratory, Mitsui Engineering & Shipbuilding Co., Ltd.
  • Kumada Makoto
    Tamano Laboratory, Mitsui Engineering & Shipbuilding Co., Ltd.
  • Miyake Yoshiaki
    Tamano Laboratory, Mitsui Engineering & Shipbuilding Co., Ltd.
  • Ohi Toshitsugu
    Tamano Laboratory, Mitsui Engineering & Shipbuilding Co., Ltd.

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  • 亜硝酸塩系インヒビターによるCr-Mo鋼の防食効果に及ぼす溶存酸素の影響
  • アショウサンエンケイ インヒビター ニヨル Cr Mo コウ ノ ボウショク

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The effect of dissolved oxygen on corrosion inhibition of Cr-Mo steel using sodium nitrite, which can be added to the circulating cooling system of marine diesel engines as a corrosion inhibitor, has been investigated in pure water with 50ppm SO42- by means of the polarization resistance method and weight loss and the corrosion potential measurements. In corrosion rates over 10mdd, there was a linear relation logarithmically between corrosion rates and polarization resistance in NaNO2-SO42- ion solutions, and critical values for polarization resistance existed in the corrosion-inhibition interfacial region. When sodium nitrite more than the critical concentration required for corrosion inhibition was added, the good inhibitive effect is obtained. On the other hand, when the sodium nitrite was added under the critical concentration in the solution with high dissolved oxygen corrosion was accelerated by the depolarization of oxygen, but corrosion was retarded with low dissolved oxygen. It can be concluded that the inhibitive action of sodium nitrite results in the formation of the adsorbed layers of nitrite ion and dissolved oxygen stimulating the passivation of the steel surface.

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