Life Prediction and Metallographical Examination of SAGBO Cracking in RB211 High Pressure Turbine Blades Available to Purchase

In a previous study, high pressure turbine blades from an RB211-24C aero-derivative industrial gas turbine engine were sectioned and metallographically examined. The turbine blades were made of cast Mar-M002, a nickel-based superalloy. It was found that stress-assisted grain boundary oxidation (SAGBO) had occurred along the inner cooling channels near the leading edge at the turbine blade root, which accelerated crack formation and propagation through dynamic embrittlement. The cracks were characterized by the presence of large Hf, Al and O concentration. It appeared that the presence of oxygen in the inner cooling channels and the rapid oxidation of hafnium carbides aggravated the onset of failure through the action of SAGBO cracking. Following this examination, a creep life prediction analysis of the RB211-24C first stage blades was performed at Life Prediction Technologies Inc. (LPTi). According to the results from LPTi’s creep life prediction, the leading edge region near the blade root is most vulnerable to combined creep and oxidation damage accumulation due to high strain accumulation, as a result of high temperatures, stress, and limited inspection ability of the inner channels. In the present study, the LPTi prediction results are compared with the metallographic analysis of RB211-24C blades. It is confirmed that SAGBO in combination with creep leads to cracking in the predicted region and the worst case creep analysis results match favorably with the field experience.