Simulation and performance study of circular ultrasonic array for tubes' internal inspection

A circular array (CA) transducer is developed and validated to implement internal inspection of the small diameter tubes, one of whose potential application targets is the heat exchanger tubes in Modular High Temperature Gas-cooled Reactor. A geometric model of the transducer and the delay law are proposed according to the inspection setup. Using k-Wave, an open source acoustic simulation toolbox, the beam profiles of various aperture sizes are analyzed to select a suitable aperture. The beams with different focal depths are compared to verify the delay law and to choose a preferable focus. Reflector responses are simulated to predict the transducer's detection sensitivity. To validate the simulation results, a prototype transducer composed of 64 elements is fabricated. Its electrical and acoustical performances are acquired with a pulser-receiver. A 4-element aperture with the focal depth of 1.0 mm is selected to perform internal inspection experiment according to the simulation results. The eight longitudinal grooves with widths of 0.2, 0.3, 0.4, and 0.5 mm on inner and outer tube walls are applied as typical reflectors to test circumferential detection sensitivity. The other five grooves with depths from 0.1 mm to 0.5 mm are chosen to verify radial detection sensitivity. The experiment results demonstrate the detection sensitivity of the CA transducer reaches at least 0.2 mm in circumferential direction and 0.1 mm in radial direction. The CA is proven capable of inspecting small diameter tubes.