A Pragmatic Approach for Estimating Residual Life of Micro cracked 17.5MW Turbine-Generator Shafts of Hydropower Plants Through Reassessment of NDT and Fracture Mechanics- A Case Study

The present study emphasizes the Residual Life Assessment of a vertical Turbine and Generator rotor shaft of an uprated 17.5 MW hydro plant by Ultrasonic B-scan imaging , followed by the assessment of the remaining life through fatigue crack growth rate studies The complete turbine shaft geometry was scanned, and the accessible regions of the generator shaft were also analyzed using UT-Bscan. The size and depth of the defect data were obtained. Finite element analysis was carried out to evaluate stresses experienced in the shaft at different locations using the commercial code Ansys Mechanical®. The residual life of the rotor shaft was calculated based on the fracture mechanics principle using the code Ansys and FRANC3DTM, considering the crack close to the shaft's OD surface. For the precise estimation of the residual life of the shaft, the optimized crack growth parameters linked to the expended service hours after the previous inspection were adopted. Keywords: Hydro turbine generator, damage tolerance, crack growth rate, stress analysis