Steam Turbine Disc Cracking Experience Volume 2: Data Summaries and Discussion

摘要

The objectives of Tasks 1 and 2 of RP 1398-5, \"Cracking of Steam Turbine Discs,\" are to identify key variables for cracking in bores and keyways and in rim attach¬ments of shrunk-on discs used in low-pressure (LP) rotors in U.S. nuclear power plants. A review was conducted of available data concerning disc cracking experi¬ence in other countries, factors governing stress corrosion cracking of low-alloy steels, and factors determining environments present in LP turbines. Disc cracking experience in U.S. plants and the characteristics and operating histories of a number of U.S. plants were determined from a survey of U.S. utilities and a series of visits to utilities.\nThe data collected suggest that relationships exist between disc cracking experi¬ence in LP turbine rotors of U.S. nuclear plants and: rotor manufacturer, including keyway design and stress levels at bores and keyways;location of the saturation line;concentrations of oxygen and copper in water-steam systems;condenser cooling water used;and condenser leakage. Limited data suggest that a relationship may exist between the depth of disc cracks and number of plant startups. Available data suggest that crack growth rates depend upon the yield strength of the disc steel used and temperature.