Creep crack growth and remaining life for the blade-fit area of a high pressure turbine rotor
- Material Integrity Solutions, Inc., Berkeley, CA (United States)
High stress areas of high pressure (HP) rotors operating in the creep regime can soften over time and lead to lifting of the blade-fit hooks, bulging of the bore, and eventually cracking and failure. This problem has been observed on the 1st stage of rotors which are CrMoV steel, similar to A-470 Class 8. The remaining life of the blade-fit area consists of a crack initiation and a growth phase. Classical creep life calculations using the Larson-Miller Parameter (or equivalent) does not consider the crack growth phase; and, classical stress analysis of these sections ignores changes in the load transfer between the blade-root and the rotor-steeple. Such simplifications lead to overly conservative estimates for the remaining life. In this study, a new technique was developed to estimate the life of the blade-fit area of HP rotors subjected to creep. This technique uses finite element (FE) based stress and fracture mechanics analyses. In this technique a sequential and time-increment crack (STIC) growth model was developed that combines the crack initiation phase with crack growth phase occurring in different blade-fit hooks. Effects of creep deformation and cracking on the load transfer between the blade and the rotor are included. The remaining life using this technique is developed in deterministic or probabilistic values. The STIC approach was applied to a specific case where blade lifting had been observed. Through its application, a probability of failure vs. time for this rotor was developed for an inspection and repair program.
- OSTI ID:
- 549983
- Report Number(s):
- CONF-961006--; ISBN 0-7918-1796-2
- Country of Publication:
- United States
- Language:
- English
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