- Safe-life analysis of low pressure rotors affected by stress corrosion cracking at disk steeples and rotor bore keyways.
- Repair criteria and acceptance for dovetail cracking and disk repairs. Independent integrity evaluations and third party review of OEM recommendations on rotor repairs and retirement.
- Failure analysis and root cause determination of service problems. Economic and technical decision analysis on inspect/run/repair/replacement options. Strategic analysis and life management evaluations.
- Preparation and review of bid specifications for new rotors and associated equipment.
Background
Our services intergrate information from several areas and technologies which include thermodynamics, static and dynamic stress analysis, fracture mechanics, materials and metallurgy, nondestructive examination, probabilistic analysis, and combined studies which involve industry and individual fleet experiences with engineering modeling to forecast future performance. Our evaluations generally enable significant cost savings for the equipment owner due to better understanding and management of equipment aging issues, increased remaining life, improved maintenance practices, longer reinspection intervals, and deferral of replacement or repairs to scheduled outages.
APTECH offers analysis and evaluation services for critical turbine/generator components including turbine rotors, shrunk-on discs, blade attachments, blade roots and airfoils, casings, generator rotors, and retaining rings. Our approach combines advanced analytical methods such as 3-D finite element stress analysis with in-depth experience with industry problems affecting critical components. APTECH has performed numerous evaluations on steam turbines and we have participated at Electric Power Research Institute Workshops/Conferences on both Fossil and Nuclear Turbine Applications. APTECH personnel have significant experience at major turbine/generator OEMs.
Evaluation of Dovetail Cracking and Repairs for LP Turbine Rotor
A damage management strategy was developed by APTECH to justify the continued operation of the LP rotor at a large nuclear power plant facility. Rotor life was limited by the occurrence of stress corrosion cracking at the dovetail attachments at the wet stage in LP. Cracks were repaired by local grinding and subsequent operation validated by a safe-life evaluation performed by APTECH. The analysis considered the actual location of repairs in the dovetail attachment hooks and the depth of individual excavations in a flaw evaluation that conservatively determined the service life for safe operation. This analysis allowed the rotor to operate without deblading so that derating the machine was not necessary. The evaluation also established an acceptable reinspection interval at which time a permanent repair could be performed. As a result of this assessment, a costly and extended turbine forced outage was avoided.
Aptech Engineering Services, Inc.
601 W. California Ave., Sunnyvale, California (408) 745-7000
© 2009, APTECH Engineering Services, Inc. All rights reserved.
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