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The flow accelerated corrosion (FAC) induced significant wall thinning has been detected on the secondary loop piping in a China CANDU reactor. The comparison of wall thinning on a SA106B/304 L stainless steel (SS) dissimilar metal weld joint (DMWJ) and a SA106B carbon steel (CS) same metal weld joint (SMWJ) was conducted. The localized corrosion behavior and wall thinning mechanism of the two weld joints were investigated through comprehensive macroscopic to microscopic analysis of failure morphology, high temperature electrochemical corrosion tests, and computational fluid dynamics (CFD) simulation. The results indicate that the heat affected zones (HAZ) of SA106B CS on the both weld joints experienced more severe wall thinning, whereas 304 L SS with a higher chromium content demonstrated almost complete resistance to FAC and wall thinning. The inner wall of the SA106B CS exhibits a significant number of tiger-striping shaped pits and an accumulation of corrosion products, predominantly consisting of Fe3O4. The results of electrochemical corrosion tests suggest that the significant localized wall thinning at SA106B HAZ of the DMWJ was attributed to the prominent galvanic corrosion between the CS and SS weld metal. The SA106B HAZ in the DMWJ acted as an active anode during the FAC attack and resulted in a 44.5% higher level of wall thinning compared to the SA106B HAZ in the SMWJ. The CFD simulation confirms the direct correlation between the distribution of wall shear stress (WSS) and the wall thinning rate. In addition, the larger flow disturbance caused by the weld reinforcement height (WRH) and the faster flow velocity at the downstream DMWJ results in strong liquid droplet impingement (LDI) erosion occurred on the weld metal and eventually results in the most severe wall thinning at this region. In summary, the FAC failure of weld joints on the piping of the secondary loop during long-term operation in high temperature high flow water is primarily attributed to the galvanic corrosion and the flow disturbance induced by geometry changes near the WRH.

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Failure Analysis of a Dissimilar Metal Weld Piping in the Secondary Loop of a Candu Nuclear Reactor

  • 会议论文

  • 发表日期：

    2026年

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  • Yuling You,
  • Fangyun Wu,
  • Qiuda Li,
  • Jiamei Wang,
  • Kai Chen,
  • Liang Zhao,
  • Hui Zheng,
  • Lefu Zhang

摘要

The flow accelerated corrosion (FAC) induced significant wall thinning has been detected on the secondary loop piping in a China CANDU reactor. The comparison of wall thinning on a SA106B/304 L stainless steel (SS) dissimilar metal weld joint (DMWJ) and a SA106B carbon steel (CS) same metal weld joint (SMWJ) was conducted. The localized corrosion behavior and wall thinning mechanism of the two weld joints were investigated through comprehensive macroscopic to microscopic analysis of failure morphology, high temperature electrochemical corrosion tests, and computational fluid dynamics (CFD) simulation. The results indicate that the heat affected zones (HAZ) of SA106B CS on the both weld joints experienced more severe wall thinning, whereas 304 L SS with a higher chromium content demonstrated almost complete resistance to FAC and wall thinning. The inner wall of the SA106B CS exhibits a significant number of tiger-striping shaped pits and an accumulation of corrosion products, predominantly consisting of Fe3O4. The results of electrochemical corrosion tests suggest that the significant localized wall thinning at SA106B HAZ of the DMWJ was attributed to the prominent galvanic corrosion between the CS and SS weld metal. The SA106B HAZ in the DMWJ acted as an active anode during the FAC attack and resulted in a 44.5% higher level of wall thinning compared to the SA106B HAZ in the SMWJ. The CFD simulation confirms the direct correlation between the distribution of wall shear stress (WSS) and the wall thinning rate. In addition, the larger flow disturbance caused by the weld reinforcement height (WRH) and the faster flow velocity at the downstream DMWJ results in strong liquid droplet impingement (LDI) erosion occurred on the weld metal and eventually results in the most severe wall thinning at this region. In summary, the FAC failure of weld joints on the piping of the secondary loop during long-term operation in high temperature high flow water is primarily attributed to the galvanic corrosion and the flow disturbance induced by geometry changes near the WRH.