The monitoring of fatigue crack growth in steel at high temperature is a critical issue in the power industry. Conventional ultrasonic transducers are temperature sensitive, and cannot survive high temperatures. To overcome such a difficulty, an ultrasonic transducer system that can be permanently installed on the pipe walls to monitor the wall thickness changes at high temperature was developed by the authors. In this paper, the feasibility of using this system for fatigue crack monitoring of steels at elevated temperature was investigated. Steel specimens with starter notches of 6 mm depth were designed. The steel samples were subject to a cyclic tensile load that varied between 4 kN and 40 kN at 3 Hz. The fatigue crack growth in the specimens was successfully monitored by the ultrasonic system and verified by an independent direct current potential drop (DCPD) method. A high repeatability of measurements was achieved by the ultrasonic system. The standard deviation of the estimated crack depth at each monitoring point is less than 0.16 mm.
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