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<p>To address corrosion failure of X70 pipeline steel welded joints in mountainous acidic soil and inform automatic pipeline welding in such regions, this study investigated the microstructure and corrosion mechanism of GMAW + FCAW-G welded joints under 30° high-slope conditions. Welded joints were fabricated via automated multi-layer downward welding (GMAW for root; FCAW-G for filling/cap). Corrosion behavior was simulated by immersion tests (NACE ASTMG31-12a) in acidic soil simulant (pH = 4.98, containing Cl<sup>−</sup>/SO<sub>4</sub><sup>2−</sup>) at 25 ± 2 °C for 30 days, with characterizations using SEM, White Light Interferometer, Gamry electrochemical workstation, CHI SECM, and XRD. BM (acicular ferrite, lath bainite, M-A islands), WM (cross-distributed acicular ferrite/bainite), and HAZ (polygonal ferrite, minor bainite, coarse grains with M-A) exhibited distinct microstructures and corrosion resistances. Electrochemical/SECM analyses showed upper groove HAZ had the lowest open-circuit potential (−730.8 mV), highest corrosion current density (54.1 μA/cm<sup>2</sup>), smallest polarization resistance (544.1 Ω·cm<sup>2</sup>), and thus poorest corrosion resistance. The corrosion resistance order was BM &gt; WM &gt; Lower Groove HAZ &gt; Upper Groove HAZ.</p>

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Microstructure and Corrosion Mechanism of GMAW + FCAW-G Welded Joints for Pipeline Steel in Mountainous Terrain

  • 期刊论文

  • 发表日期：

    2026年5月19日

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  • Ruinan Lin,
  • Xiaodan Wang,
  • Luyao Tang,
  • Mei Yang

摘要

To address corrosion failure of X70 pipeline steel welded joints in mountainous acidic soil and inform automatic pipeline welding in such regions, this study investigated the microstructure and corrosion mechanism of GMAW + FCAW-G welded joints under 30° high-slope conditions. Welded joints were fabricated via automated multi-layer downward welding (GMAW for root; FCAW-G for filling/cap). Corrosion behavior was simulated by immersion tests (NACE ASTMG31-12a) in acidic soil simulant (pH = 4.98, containing Cl−/SO42−) at 25 ± 2 °C for 30 days, with characterizations using SEM, White Light Interferometer, Gamry electrochemical workstation, CHI SECM, and XRD. BM (acicular ferrite, lath bainite, M-A islands), WM (cross-distributed acicular ferrite/bainite), and HAZ (polygonal ferrite, minor bainite, coarse grains with M-A) exhibited distinct microstructures and corrosion resistances. Electrochemical/SECM analyses showed upper groove HAZ had the lowest open-circuit potential (−730.8 mV), highest corrosion current density (54.1 μA/cm2), smallest polarization resistance (544.1 Ω·cm2), and thus poorest corrosion resistance. The corrosion resistance order was BM > WM > Lower Groove HAZ > Upper Groove HAZ.