Abstract | NDT and structural health monitoring (SHM) of metal pipes and plates at temperatures up to 490°C using flexible ultrasonic transducers (FUTs) are presented. These FUTs consist of a typically 75-μm thick titanium or stainless steel membrane coated with a 70 μm piezoelectric bismuth-titanate composite (BIT-c) or lead-zirconate titanate composite (PZT-c) film, and a thin top electrode. The BIT-c and PZT-c films are made with a sol-gel spray technique. The main merit of these FUTs is that they can be fabricated economically and installed on-site for NDT and SHM purposes. On-site installation using glues or brazing materials which serve as a high temperature ultrasonic couplant between the FUT and the object for inspection, will be demonstrated. One of such FUTs with a center frequency of around 12.1 MHz has been glued onto a steel pipe of 101 mm in diameter and 4.5 mm in wall thickness and operated at 300°C. The estimated pipe thickness measurement accuracy at 300°C is 8 μm. Another FUT was brazed onto a steel pipe of 25 mm in diameter and 3.5 mm in wall thickness and operated up to 490°C. Furthermore, UTs with a center frequency of about 7 MHz were glued onto the end and side edges of steel plates with a length of 406.4 mm and a width of 50.8 mm to generate and receive, predominantly shear-horizontal (SH) plate acoustic waves (PAWs) at temperatures up to 300°C. Two line defects, with 1 mm in width, 1 mm in depth, and 25.4 mm and 50.8 mm in length, at a distance of about 146.3 mm and 233.5 mm respectively away from the FUT location, could be detected by the SH PAWs. FUT arrays have been used to demonstrate the capability of monitoring crack propagation in a steel plate. |
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