Probabilistic Analysis of Turbine Disc SCC Incubation and Propagation

Stress corrosion cracking (SCC) is a common problem found on aging low-pressure turbine (LP) rotors that operate in a wet/dry stream environment. While much has been published on the growth rate of SCC in turbine rotor-disk materials, incubation time is rarely addressed. Since no effective way has been demonstrated to prevent disk rim SCC from occurring other than to replace the damaged rim with a weld repair of higher chromium content, a better understanding of incubation time could provide operators with a means to treat SCC before cracks are large enough to start to grow. This paper discusses the critical mechanisms involved in the SCC incubation, process and describes a probabilistic approach to make meaningful assessments of incubation time. Data published for General Electric turbine rotors is used to test the model.