The In-situ Phased Array Ultrasonic Testing of the Last Stage Blade About the MARKII Low Pressure Rotor

In Daya Bay nuclear plant, the type of the last stage blade of turbine rotor is MARKⅡ vertical tree root, which is designed by GEC-A. In some plants, cracks were found on the rotor blades of old type, which were not improved before by GEC-A. For that reason, Daya Bay nuclear plant began feedback preventive inspection in a very early time. But there is a problem that it has to tear down all the rotor blades before inspection each time, so the inspection will cost about 8~9 days and become the critical path of the refueling outage, whats more, it may cause the risk of mechanical damage. Therefore, to extend the cycle time of the low-pressure cylinder blades disassembly can further improve the economy of the steam turbine and keep the nuclear power plant steam turbine maintaining a reliable. Through years of researches and experiments, in-situ phased array ultrasonic inspection techniques can meet the requirement, and it has been successfully used practically.