Feasibility of Hammer Peening for Straightening of Bent Turbine Rotor after Operation based on Finite Element Analysis

This study investigates the feasibility of applying a hammer peening process to straighten bending deformation in power-generation turbine rotors after long-term operation, based on finite element analysis(FEA). A simplified cylindrical rotor specimen without initial bending deformation was fabricated. To simulate post-operation bending behavior, first and second preliminary hammer peening were applied symmetrically to the upper left and right positions relative to the center, intentionally inducing upward bending deformation at the central region. Subsequently, third hammer peening was performed at the lower central position to correct the induced bending deformation toward a near-linear configuration. After each peening stage, run-out measurements were conducted to evaluate changes in rotor bending deformation. In parallel, a finite element model of the turbine rotor was developed, and hammer peening simulations corresponding to the first through third stages were performed under the same conditions as the experiments. Deformation curves along the rotor shaft centerline obtained from the simulations were compared with eccentricity values calculated from the experimental run-out data. The results showed close agreement between the predicted bending deformation and the experimentally derived eccentricity. Furthermore, the bending deformation induced after the first and second peening stages was clearly reduced after the third peening applied in the opposite direction. These results confirm that the proposed hammer peening numerical model can effectively and accurately predict and straighten bending deformation in turbine rotors of various diameters and lengths after operation.