Development and Experimental Study of an Electromagnetic Ultrasonic Circumferential Guided Wave Transducer That Self-Adapts to the Curvature of High-Temperature Pipeline

In the petroleum, chemical, nuclear, electric power, and other fields, there are quite a lot of high-temperature pipelines and supports, but there is a current lack of effective detection of these pipelines and their shield areas. A pair of water-cooled high-temperature electromagnetic ultrasonic circumferential wave transducers are designed through experiments to solve the problem of difficult detection at high-temperature pipeline shielding areas. To solve the problem of large acoustic wave loss caused by the support structure, the transducer is designed to self-adapt to the surface of the pipe to improve the efficiency of excitation and reception. After testing, the developed transducer is more efficient than the traditional transducer, which is based on ceramic plate. The hole defects with a diameter of 3 mm and a depth of half the wall thickness can be detected after 10 min of continuous detection on the P91 pipe surface (up to $630~^{\circ }$ C), and the defect signal is very stable. Compared to $25~^{\circ }$ C, the amplitude is reduced by 48%. On the Q235 pipe (up to $630~^{\circ }$ C), through holes with the smallest diameter of $\varphi ~3$ mm can be detected across the support. When the contact time is brief, the amplitude of $630~^{\circ }$ C is 6.9 times that at room temperature, but the signal is unstable. Furthermore, the higher the temperature, the faster the amplitude decreases with time. When the contact time is greater than 5 min, the maximum signal amplitude appears at about $350~^{\circ }$ C.