Simplified methods of steam turbine blade root life analysis
- Packer Engineering, Inc., Pittsburgh, PA (United States)
- San Diego Gas and Electric, CA (United States)
- Allegheny Power System, Greensburg, PA (United States)
Simplified and approximate methods are presented for evaluating the remaining life, acceptable flaw limits, and reinspection interval of low pressure steam turbine blade roots. The approach involves examining all the relevant features of blade root behavior, rather than only one aspect in detail. More specifically, the inspection and cracking history for the particular machine, the metallographic and fractographic evidence from cracked blades, the estimated stress profiles near blade root serrations, and the fracture mechanics material property data are taken in to consideration. Striation and beach mark spacings can sometimes be used to estimate crack growth rates and local stresses. Sharply decreasing stress gradients produce constant or decreasing stress intensity factors with depth, which in turn forestall accelerating or runaway crack growth rates. Recognition of the crack growth rate threshold often leads to the finding that cracking is due to transient events, rather than the continuous vibratory stress levels. This approach is valuable for providing guidance on run/repair/replace strategies, confirming service experience, and determining if and what type of more detailed analysis should be conducted. Some general examples involving common low pressure steam turbine blades are given.
- OSTI ID:
- 82750
- Report Number(s):
- CONF-941007--; ISBN 0-7918-1382-7
- Country of Publication:
- United States
- Language:
- English
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