The use of guided ultrasonic waves has been identified as a promising technology for continuous monitoring of pipes and tubes for the detection of corrosion damage defects of cross-sectional area ratio less than 5%, particularly in the process industry applications. Here, we present an approach to use torsional guided wave mode T(0,1) generated using leave-in-place magnetostriction patch sensors for the health monitoring of thin and small diameter stainless steel tubes operating at elevated temperatures in the range of 150°C. These tubes are used in the transportation of gas in the Silicon wafer manufacturing semiconductor industries. The detection of small pitting defects is demonstrated using both numerical and experimental approach. The phenomenon of scattering of the high frequency fundamental torsional guided wave mode T(0,1) from small pitting type defects in thin and small diameter tubes is closely examined, and its excitation parameters are selected using finite element (FE) simulations. The sensitivity of the reflected signal from defects as low as 2% of the cross-sectional area ratio was feasible even at high temperature. This work is of great interest to many processes in semiconductor manufacturing. © 2021 Korea Institute for Structural Maintenance and Inspection.