Development of ultrasonic phased array technique for inspection of fir-tree type turbine blade root and disc-rim in nuclear power plant

Steam turbines are crucial in both nuclear and thermal power plants, serving a key role in electricity generation. However, the operational lifespan of these turbines is often limited by failures in the turbine blade roots and disc rims due to fatigue, stress corrosion cracking and creep. Usage of reliable non-destructive technique during in-service inspection of turbine assembly is very important for decision making and safe operation of power plant. The conventional ultrasonic technique which is being employed currently suffers from access limitation, high inspection time and false calls during defect detection due to complex geometry of blade roots and disc rims. To address these issues, an advanced ultrasonic inspection technique using phased array technology was developed, specifically tailored for fir-tree type blade roots and disc rims. Ultrasonic Simulation studies were performed to determine the optimal parameters for phased array probes, ensuring the effective detection and precise sizing of crack-like defects. This manuscript presents the findings from these simulations, along with experimental results from phased array inspections of turbine blade root and disc rim mockup of turbine assembly in nuclear power plant.