Acoustic emissions from crack growth in steam turbine rotor steels. Final report
This report provides the results of an experimental characterization of the acoustic emission resulting from fatigue crack growth in steam turbine rotor steels. Such result provides guidance in the development of on-line acoustic emission monitoring techniques for crack growth in rotors. Additionally, the results provide the first steps toward an ability to quantitatively relate acoustic emission to crack extension in rotors. Experiments were performed on specimens fabricated from a retired rotor in which cracks were grown under well-controlled laboratory conditions while simultaneously monitoring for acoustic emission. This allowed quantitative empirical relations to be drawn between acoustic emission and fracture mechanics parameters. Such relations are well suited for extrapolation to operating turbine rotors. It was found that the best correlation between acoustic emission and fracture mechanics parameters was between the number of acoustic emission events per cycle and the strain energy released by crack extension per cycle. The acoustic emission was not strongly influenced by the location of the specimen from the rotor, or the test temperature (within the range of 21 to 121/sup 0/C), and the major source of acoustic emission was apparently the cracking of inclusions. The empirical acoustic emission-fracture mechanics relations were combined with a fracture mechanics analysis of fatigue crack growth in an operating turbine in order to estimate the number of acoustic emission events observable as a cracked rotor approached failure. It was predicted that 17 to 260 events would be observed during the 500 cold starts considered as leading to failure. This small number of events indicates that care must be used in the development of on-line monitoring instrumentation. Such information serves as a valuable input to future efforts to conceptualize and develop an on-line acoustic emission instrumentation system for steam turbine rotors.
- Research Organization:
- Science Applications, Inc., Sunnyvale, CA (USA)
- OSTI ID:
- 6949612
- Report Number(s):
- EPRI-CS-3428; ON: TI84920316
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
200100* -- Fossil-Fueled Power Plants-- Power Plants & Power Generation
42 ENGINEERING
420500 -- Engineering-- Materials Testing
ACOUSTIC EMISSION TESTING
ACOUSTIC MONITORING
ACOUSTIC TESTING
ALLOYS
CRACK PROPAGATION
FATIGUE
FRACTURE MECHANICS
IRON ALLOYS
IRON BASE ALLOYS
MACHINERY
MATERIALS TESTING
MECHANICAL PROPERTIES
MECHANICS
MONITORING
NONDESTRUCTIVE TESTING
ROTORS
STEAM TURBINES
STEELS
TESTING
TURBINES
TURBOMACHINERY