Failure study of steam turbine Last-Stage rotor blades under a High-Speed wet steam environment

The failure mechanism of the last-stage rotor blade of the low-pressure cylinder of a steam turbine when exposed to high-speed wet steam was elucidated. The results indicated that the combined effects of water erosion, stress corrosion, and corrosion fatigue resulted in the failure of the shroud-lacing wire section (which was made of martensitic stainless steel through the highfrequency induction hardening method) on the steam inlet side. Furthermore, the combined action of the water hammer pressure of the secondary water droplets and the pressure of the cavitation jet caused water erosion and the formation of pits. Additionally, the combined action of the stress concentration at the ends of the pits, the stress concentration at the inlet side structure, and the alternating stress-induced crack initiation at the inlet-side shroud-lacing wire section. Finally, the crack propagation was accelerated by the combined action of stress corrosion and corrosion fatigue. This study provides theoretical guidance for inhibiting the growth of pits and prolonging the fatigue life of blades.