Quality control of seal discs - Through NDT

Seal disc is used to prevent the leakage of heavy water from coolant channel in 235-MWe Pressurised Heavy Water Nuclear Reactors. The nickel ring which serves as a sealing gasket, is diffusion bonded to a SS 17-4-pH disc. Fluorescent wet magnetic particle test, focused ultrasonic beam immersion test and liquid penetrant test were used to detect raw material defects, bonding defects and process introduced defects. Bonding defect of the order of O.16mm at 1.8mm below the front surface of the nickel ring was revealed by the ultrasonic test. This paper presents a brief description of different NDT techniques used for testing seal disc, their justifications and applicable acceptance standards.