Corrosion of Carbon Steel in Tap Water （Ⅱ）

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Other Title
  • 水道水環境における炭素鋼の腐食（Ⅱ）
  • 水道水環境における炭素鋼の腐食(2)腐食生成物による表面被覆率と腐食電位の関係
  • スイドウスイ カンキョウ ニ オケル タンソコウ ノ フショク(2)フショク セイセイブツ ニ ヨル ヒョウメン ヒフクリツ ト フショク デンイ ノ カンケイ
  • ―Growth of Rusted Area on Metal Surface in Relation to Corrosion Potential―
  • ―腐食生成物による表面被覆率と腐食電位の関係―

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Abstract

<p>This research was focused on the growth of rusted areas on the surface of carbon steel in tap waters, which were collected at 66 locations in Japan.</p><p>Rusted area ratio （θ） was defined as θ＝Arust/A, where A was total surface area and Arust was the area covered with corrosion products. The changes of θ and corrosion potential （Ecorr） with time were investigated.</p><p>The followings （1）-（6） were resulted.</p><p>（1）As immersion time elapsed, θ increased and Ecorr became less noble.</p><p>（2）The abrupt changes in θ and Ecorr with time appeared simultaneously. Stagnations of both θ and Ecorr followed the above. The time of the abrupt change depended on quality of the tap water.</p><p>（3）The relationship between log{θ/（1－θ）} and Ecorr was similar regardless of water quality.</p><p>This meant that the rusted area could be estimated only by measuring Ecorr.</p><p>（4）The abrupt change was in θ seen from 0.2 to 0.5 and Ecorr from －300 to －500 mV vs.SSE, the time at which Ecorr reached －400 mV was defined as tinitial. For larger tinitial, the corrosion at small θ rusted longer.</p><p>（5）Both average and maximum localized corrosion rates were closely related to tinitial. Insight into those relations surmised the following mechanisms;</p><p>（a）When θ＜0.2, the anodes were fixed, inducing localized corrosion.</p><p>（b）When θ＞0.5, anodic and cathodic reactions were distributed even on the whole surface, resulting in then uniform corrosion.</p><p>（6）The authors found that the maximum localized corrosion rate, vmax（mm y－1） was a function of tinitial as vmax＝0.32×tinitial1/3. The unit of tinitial in this equation was hour.</p>

Journal

  • Zairyo-to-Kankyo

    Zairyo-to-Kankyo 70 (9), 295-301, 2021-09-10

    Japan Society of Corrosion Engineering

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