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Inspection and Modeling Analysis of Locking Pins in the Penultimate-Stage Blades of a 600 MW Steam Turbine.

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Title: Inspection and Modeling Analysis of Locking Pins in the Penultimate-Stage Blades of a 600 MW Steam Turbine.
Authors: Tang, Ke1 (AUTHOR), Chen, Weiwen2 (AUTHOR), Zhu, Jiang1,3 (AUTHOR), Yi, Binhao1,4 (AUTHOR), Hao, Qing1,5 (AUTHOR), Gao, Jiashun1,2,3 (AUTHOR), Xu, Zhilong2,4,5 (AUTHOR) zhilong.xu@163.com, Guo, Bicheng2,3,5 (AUTHOR), Chen, Shiqi2,4,5 (AUTHOR)
Source: Materials (1996-1944). Oct2025, Vol. 18 Issue 19, p4487. 15p.
Subjects: Stress corrosion cracking, Fretting corrosion, Service life, Finite element method, Fracture mechanics, Metallurgical analysis, Steam-turbines
Abstract: The fracture behavior of a locking pin used in the penultimate-stage blades of a 600 MW steam turbine in a thermal power plant was investigated through microstructural and microhardness characterization, fracture surface and energy-dispersive spectroscopy (EDS) analysis, as well as finite element load simulation. The microhardness values measured on the cross-section of the service pins ranged from 528 to 541 HV0.1, showing little difference from the unused pins. Scanning electron microscopy analysis revealed that approximately 70% of the fracture surfaces exhibited an intergranular "rock candy" morphology. The results indicate that pin failure was primarily caused by the combined effects of fretting wear and stress corrosion cracking (SCC). Specifically, vibration at the blade root, impeller, and pins due to start–stop cycles and load variations led to fretting wear, forming pits approximately 75 μm in size. Under the combined effects of weakly corrosive wet steam environments and shear stresses, SCC initiated at the high stress concentration points of these pits. Early crack propagation primarily followed original austenite grain boundaries, while later stages mainly extended along martensite plate boundaries. As cracks advanced, the cross-sectional area gradually decreased, causing the effective shear stress to increase until it exceeded the shear strength, ultimately leading to fracture. These findings not only provide a scientific basis for enhancing the reliability of steam turbine locking pins and extending their service life, but also contribute to a broader understanding of the failure mechanisms of key components operating under corrosive and fluctuating load environments. [ABSTRACT FROM AUTHOR]
Copyright of Materials (1996-1944) is the property of MDPI and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
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  Data: Inspection and Modeling Analysis of Locking Pins in the Penultimate-Stage Blades of a 600 MW Steam Turbine.
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  Data: <searchLink fieldCode="JN" term="%22Materials+%281996-1944%29%22">Materials (1996-1944)</searchLink>. Oct2025, Vol. 18 Issue 19, p4487. 15p.
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  Data: <searchLink fieldCode="DE" term="%22Stress+corrosion+cracking%22">Stress corrosion cracking</searchLink><br /><searchLink fieldCode="DE" term="%22Fretting+corrosion%22">Fretting corrosion</searchLink><br /><searchLink fieldCode="DE" term="%22Service+life%22">Service life</searchLink><br /><searchLink fieldCode="DE" term="%22Finite+element+method%22">Finite element method</searchLink><br /><searchLink fieldCode="DE" term="%22Fracture+mechanics%22">Fracture mechanics</searchLink><br /><searchLink fieldCode="DE" term="%22Metallurgical+analysis%22">Metallurgical analysis</searchLink><br /><searchLink fieldCode="DE" term="%22Steam-turbines%22">Steam-turbines</searchLink>
– Name: Abstract
  Label: Abstract
  Group: Ab
  Data: The fracture behavior of a locking pin used in the penultimate-stage blades of a 600 MW steam turbine in a thermal power plant was investigated through microstructural and microhardness characterization, fracture surface and energy-dispersive spectroscopy (EDS) analysis, as well as finite element load simulation. The microhardness values measured on the cross-section of the service pins ranged from 528 to 541 HV0.1, showing little difference from the unused pins. Scanning electron microscopy analysis revealed that approximately 70% of the fracture surfaces exhibited an intergranular "rock candy" morphology. The results indicate that pin failure was primarily caused by the combined effects of fretting wear and stress corrosion cracking (SCC). Specifically, vibration at the blade root, impeller, and pins due to start–stop cycles and load variations led to fretting wear, forming pits approximately 75 μm in size. Under the combined effects of weakly corrosive wet steam environments and shear stresses, SCC initiated at the high stress concentration points of these pits. Early crack propagation primarily followed original austenite grain boundaries, while later stages mainly extended along martensite plate boundaries. As cracks advanced, the cross-sectional area gradually decreased, causing the effective shear stress to increase until it exceeded the shear strength, ultimately leading to fracture. These findings not only provide a scientific basis for enhancing the reliability of steam turbine locking pins and extending their service life, but also contribute to a broader understanding of the failure mechanisms of key components operating under corrosive and fluctuating load environments. [ABSTRACT FROM AUTHOR]
– Name: AbstractSuppliedCopyright
  Label:
  Group: Ab
  Data: <i>Copyright of Materials (1996-1944) is the property of MDPI and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.)
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      – Type: doi
        Value: 10.3390/ma18194487
    Languages:
      – Code: eng
        Text: English
    PhysicalDescription:
      Pagination:
        PageCount: 15
        StartPage: 4487
    Subjects:
      – SubjectFull: Stress corrosion cracking
        Type: general
      – SubjectFull: Fretting corrosion
        Type: general
      – SubjectFull: Service life
        Type: general
      – SubjectFull: Finite element method
        Type: general
      – SubjectFull: Fracture mechanics
        Type: general
      – SubjectFull: Metallurgical analysis
        Type: general
      – SubjectFull: Steam-turbines
        Type: general
    Titles:
      – TitleFull: Inspection and Modeling Analysis of Locking Pins in the Penultimate-Stage Blades of a 600 MW Steam Turbine.
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            NameFull: Tang, Ke
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            – D: 01
              M: 10
              Text: Oct2025
              Type: published
              Y: 2025
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