Analysis on NDE Problem of Weld Joint between AP1000 Steam Generator and Reactor Coolant Pump Casing

For the problems of unacceptable imperfection indications found in the weld joint between AP1000 Steam Generator and RCP Casing during Ultrasonic Examination（UT）, the comparison of UT inspection techniques have been demonstrated for different UT Procedures, and examination sensitivities difference have been analyzed between ASME Section Ⅺ and Section Ⅲ. It is proved that ASME Section Ⅺ inspection techniquesof in-service inspection were mixed with Section Ⅲ acceptance standardsof examination for fabrication, which is the immediate cause why imperfection indications were unacceptable. Furthermore, the re-UT was performed by several different degree probes with examination sensitivities established on an added hole reflector in the UT block. It is found that imperfection identity of UT indications were misidentified by original operators, and finally proved that this weld joint meet the requirement of acceptance standards of ASME Section Ⅲ.