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Analysis on corrosion fatigue cracking mechanism of 17-4PH blade of low pressure rotor of steam turbine
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  • Yuwei Wei,
  • Yongjun Li,
  • Jiafeng Lai,
  • Qinxin Zhao,
  • Lili Yang,
  • Qingyu Lin,
  • Xiaolin Wang
Yongjun Li
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Jiafeng Lai
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Qinxin Zhao
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Qingyu Lin
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Xiaolin Wang
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Abstract: The causes of many blade fractures of a steam turbine in a power plant were analyzed by means of macro analysis, mechanical examination, metallographic examination, SEM and X-ray fluorescence spectrum analysis(XRF). The results show that the blade cracks due to corrosion fatigue. Cl -, K +, etc. react with the turbine blades in the steam environment in physical, chemical and electrochemical ways, causing local spot corrosion on the blades, forming corrosion pits.In addition, the steam condensate has an erosion effect on the blades, both of which form a corrosion fatigue source. The autocatalytic process of block cell is formed when Cl -, K +, etc. react with the turbine blades. Under the action of complex load, the current density i of activation dissolution of metal can be expressed as a function of complex stress state .Crack growth has an important relationship with stress, depth and width of corrosion pits. The larger the width of corrosion pit is, the deeper the depth is, the smaller threshold nominal stress range for crack elongation 〖∆σ〗_th is, the easier the blade cracks. Under the external conditions of complex alternating stress formed by tensile force, bending force, torsion force and exciting force, the complex alternating stress directly promotes the crack propagation until the fracture failure. Keywords:XRF;Corrosion fatigue;Corrosion pit;Threshold nominal stress range for crack elongation 〖∆σ〗_th;Complex alternating stress