Fillet welds in small-diameter pipe socket of pressure vessels always have complicated structures and groove types, which make it easy to produce porosity, lack of fusion, incomplete penetration and other flaws during welding. Therefore, nondestructive testing is a significant and meaningful approach to ensure the quality of welding for pressure vessels’ safety. Ultrasonic testing is the main method for nondestructive testing of pipe fillet welds. However, it is difficult to distinguish between the interference wave and the flaw echo, or to recognize the defect signal, while utilizing conventional ultrasonic testing technology. Additionally, the coupling effect is bad for traditional rigid probe on the concave surface when the probe is inserted into the small-diameter pipe to do the inner scanning. To obtain a good coupling effect, flexible phased array technology was put forward, with a bendable probe made from flexible materials. The probe could be bent and inserted into the inner pipe for longitudinal wave scanning, giving a good matching with the inner wall and replacing the traditional rigid probe. Besides, it is more convenient to conduct the ultrasonic testing, and the focal law could be changed easily according to the curve shape of the inner pipe, without replacing the probe. Thus, scanning and dynamic focusing in multiple angles and directions can be carried out, and the position, distribution and size of the flaws could be displayed intuitively combined with real-time imaging technology. This technology is able to obtain better coupling and detecting effects and solve the technical problem for concave ultrasonic inspection of fillet welds.

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