Condition Assessment of Generator Rotor Shaft of 108 MW Hydro Plant Through Phased Array Ultrasonic Technique and Estimation of Remaining Life Through Finite Element Analysis

The Condition Assessment of Generator rotor shaft of typical 108MW plant has been carried out involving the application of advanced Phased Array Ultrasonic Technique (PAUT)to quantify the volumetric nature of the defects in the rotor. This technique involves mapping of the entire rotor volume in different segments and layers using multiple ultrasonic sensors. The imaging of defects in the rotor shaft was carried out in four different diameter sections 558 mm, 610mm, 737 mm and 914 mm. The scanning of entire shaft geometry regions was done following different patches from top to bottom portion of the shaft by PAUT and analysis of individual scanning results for evaluation of crack size, position inside the rotor geometry and orientation. The critical defects identified by this technique with their locations and orientation inside the rotor has been presented. The stress and fatigue life of the shaft under defect free conditions have been carried out by finite element analysis using the commercial code Fe-Safe^TM. The calculation of remaining life of the rotor shaft was carried out based on the principle of fracture mechanics using the code ZENCRACK^TM. The results of the crack growth rate data of critical cracks close to the surface were presented.