Ultrasonic transducers typically used for inspection such as wall thickness measurement are not suitable for high temperature applications and the inspections are more of a periodic and manual in nature instead of continuous. A waveguide based method combined with synthetic focusing image reconstruction has been proposed for Structural Health Monitoring (SHM) of the components operating in hostile environments and is sometimes too complex and inaccessible for manual inspection. This work follows to develop a waveguide based sensing method to implement a robust and accurate monitoring of surface back wall damage with moderate coverage range. Finite Element (FE) Analysis has been carried out to study the multi-modal behavior in waveguides of rectangular cross sectional geometry and to choose optimal mode(s) and geometry which are best suited for the application. Simulations based on 3D Elastodynamic and 2D Acoustic FE models has been taken to study and implement the reconstruction for different cases representing various levels of wall loss. The waveguide is being used for transmitting the ultrasonic guided waves into the structure under investigation and the received signals from the structure has been processed using Synthetic focusing technique for the surface back wall reconstruction to access damage caused by corrosion like phenomenon. © 2019 SPIE.