Ultrasonic technology has developed rapidly in decades. However, few ultrasonic technologies have been proposed for tubes’ internal inspection. In this paper, 6 types of ultrasonic endoscopic transducers are brought to detect volumetric and planar flaws in tubes. Steam generator tube is application target. Beam simulations are implemented and compared using an open source acoustic simulation toolbox to illustrate beneficial effects of the different transducers. The results show the proposed endoscopic array transducers can form focused ultrasonic beams in tube wall, which do helps when detecting complex defects, such as crevice with uncertain direction. A prototype circular array transducer with 64 elements is fabricated to demonstrate the design. A straight tube (Φ19 × 3mm) made of carbon-steel with 8 longitudinal grooves and 8 ring grooves of no more than 0.5mm width on both inner and outer tube wall are applied in endoscopy experiments. The results demonstrate the detection sensitivity of the circular array transducer reaches 0.2mm in both circumferential direction and axial direction. The combination of the above proposed transducers and advanced imaging algorithms such as total focusing method may build an integrated array ultrasonic endoscopic inspection scheme for the internal inspection of tubes.

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