Corrosion Fatigue Evaluation on Low-pressure Steam Turbine
A retired low-pressure steam turbine rotor has been investigated and results showed that cracks were initiated from pits on the first hook of the L-2 stage, and that the probability of crack initiation increased when pits reached a critical depth of around 0.2mm. The fracture surface of a damaged rotor showed striations related to corrosion fatigue. To investigate pit initiation and the effect of a corrosive environment on pit growth in 3.5Ni-Cr-Mo-V steam turbine rotor steel, immersion tests and pit current density tests were performed in deionized water and in 10-100ppm NaCl solutions at 25℃. To evaluate long-term fatigue strength, corrosion fatigue tests were also carried out in air, in deionzed water and in a 5000ppm NaCl solution at 80℃ up to 10<8 stress cycles. Scanning electron microscope (SEM) and X-ray cartography analysis results showed that pits initiated from inclusions like MnS. Chloride then concentrated in the pits and its corrosive effect accelerated pit growth. Long-term corrosion fatigue strength was reduced, and pit growth and fatigue crack initiation from the pit can be considered as the main factor in reducing corrosion fatigue strength. A new cleaning technique combining ultrasonic and chemical cleaning techniques was developed to remove many years’ accumulation of rust covering the disk hooks of the L-2 stage. Results show that almost all the rust inside the pits can be removed.
Steam turbine Pits Crack Corrosion fatigue
L. Yan S Inagaki M. Arimura
Toshiba Corporation/Power & Industrial Systems R&D Center 2-4 Suehiro-cho, Tsurumi-Ku, Yokohama 230, Toshiba Corporation/Keihin Product Operations/Steam Turbine Department 2-4 Suehiro-cho, Tsurumi-Ku,
国际会议
2007杭州国际动力工程会议(The International Conference on Power Engineering 2007)
杭州
英文
2007-10-23（万方平台首次上网日期，不代表论文的发表时间）