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<p>Pitting corrosion significantly affects the lifespan of oil-casting steel. This study investigated the pitting corrosion behavior and corrosion layer characteristics of cerium-treated oil casing steel in a 4 pct NaCl solution containing 0.01 mol·L<sup>−1</sup> Na<sub>2</sub>S at pH 4 and 25 °C. It was found that the pitting corrosion induced by CaO·2Al<sub>2</sub>O<sub>3</sub>–CaO·6Al<sub>2</sub>O<sub>3</sub>, Ce<sub>2</sub>O<sub>3</sub>, and Ce<sub>2</sub>O<sub>2</sub>S inclusions resulted from both chemical dissolution and the formation of micro-crevices at the inclusion/matrix interfaces. The low self-dissolution tendency of CeAlO<sub>3</sub> inclusions exhibited an inhibitory effect on the pitting propagation. Furthermore, Ce promoted the formation of a thin and dense corrosion layer. During corrosion layer formation, the outward diffusion of Cr and Mo ions was suppressed by Ce diffusion occupying the active sites, which led to the enrichment of Cr and Mo in the corrosion layer. In this study, the optimum Ce content for corrosion resistance in oil casing steel should be in the range of 61 to 120 ppm.</p>

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Effect of Rare Earth Metal Alloying on Pitting Corrosion Resistance and Corrosion Layer Formation of High-Strength Oil Casing Steels

  • 期刊论文

  • 发表日期：

    2025年9月24日

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  • Yu-yu Liang,
  • Pei-yuan Ni,
  • Ying Li,
  • Yu-Lung Chiu

摘要

Pitting corrosion significantly affects the lifespan of oil-casting steel. This study investigated the pitting corrosion behavior and corrosion layer characteristics of cerium-treated oil casing steel in a 4 pct NaCl solution containing 0.01 mol·L−1 Na2S at pH 4 and 25 °C. It was found that the pitting corrosion induced by CaO·2Al2O3–CaO·6Al2O3, Ce2O3, and Ce2O2S inclusions resulted from both chemical dissolution and the formation of micro-crevices at the inclusion/matrix interfaces. The low self-dissolution tendency of CeAlO3 inclusions exhibited an inhibitory effect on the pitting propagation. Furthermore, Ce promoted the formation of a thin and dense corrosion layer. During corrosion layer formation, the outward diffusion of Cr and Mo ions was suppressed by Ce diffusion occupying the active sites, which led to the enrichment of Cr and Mo in the corrosion layer. In this study, the optimum Ce content for corrosion resistance in oil casing steel should be in the range of 61 to 120 ppm.