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Premature failure of steam turbines is a problem in both manufacturing operations and power generation plants. Information on the influence of contaminant sodium chloride in steam on the corrosion fatigue life of Type 403 stainless steel, the most common steam-turbine blade material, is needed. High-frequency fatigue tests were conducted on bare specimens of Type 403 steel, both in a pure-steam environment at 250 F, and in steam contaminated with small quantities of sodium chloride. Tests were also conducted on shot-peened specimens diffusion-coated for corrosion protection. With 2000 ppm of salt in the steam, considerable reduction in fatigue life was observed for bare steel in relatively brief tests at high ultrasonic frequencies. Considerable increase in fatigue life was observed for the shot-peened and coated specimens. The results show that even trace quantities of a corrodent at elevated temperatures can greatly reduce fatigue lifetimes of steam-turbine blade material. The effectiveness of the coating system was demonstrated clearly in these tests, suggesting important increases in the operational lifetimes of steam-turbine equipment.
fatigue (materials), corrosion fatigue, stainless steels, ultrasonic frequencies, corrosion, corrosion prevention, diffusion coating, shot peening, fractures (materials), fractography
Principal research scientist, Hydronautics, Inc., Laurel, Md.
Research fellow, E. I. duPont de Nemours and Co., Inc., Wilmington, Del.