Ultrasonic Crack Monitoring Using SH Waves in extreme and inaccessible environments

The development of SH waveguide probes that can work under extreme conditions (Temperature>500°C, radiation) has opened up the possibility to carry out ultrasonic monitoring using SH waves on plant components that cannot be inspected otherwise. The deployment of such monitoring devices can result in substantial economic benefit by continuously supplying information about the state of a critical plant component rather than only at periods of shut down, which can be years apart. SH waves are often impractical in manual NDT due to coupling issues; however when permanently installed the simplicity of their interaction with defects becomes very attractive. This paper presents different crack size monitoring techniques using SH waves and highlights their advantages and disadvantages. Simulated as well as experimental results for laboratory specimens are presented.