Inspection and Modeling Analysis of Locking Pins in the Penultimate-Stage Blades of a 600 MW Steam Turbine
Ke Tang, Weiwen Chen, Jiang Zhu, Binhao Yi, Qing Hao, Jiashun Gao, Zhilong Xu, Bicheng Guo, Shiqi Chen
TL;DR
This paper investigates why locking pins in a large steam turbine break down, finding that wear and corrosion together cause failures.
Contribution
The study identifies the combined role of fretting wear and stress corrosion cracking in locking pin failure, with detailed microstructural and simulation analysis.
Findings
Microhardness values of used and unused pins showed minimal difference.
Fracture surfaces showed intergranular morphology due to stress corrosion cracking.
Crack propagation followed grain and martensite boundaries, leading to eventual fracture.
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…
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Taxonomy
TopicsHydrogen embrittlement and corrosion behaviors in metals · High Temperature Alloys and Creep · Mechanical stress and fatigue analysis