Super heater tubes are subjected to alternate heating and cooling in power plants causes crack and eventually fail. This phenomenon is termed as thermal fatigue. In this paper, a laboratory simulation for reproducing thermal fatigue phenomenon is developed to determine the number of cycles of failure occurs in super heater tubes. Thermal fatigue tests are conducted in Non-Destructive Tested T23 base and SMAW welded tubes separately. The tubes are subjected to thermal cycles from 800C (accelerated temperature) to room temperature (28C). In this work 800C is selected in order to achieve the crack much earlier. The selected temperature is just below the Ac1 temperature. The tubes are subjected to heat by Oxy-acetylene flame and subsequently quenched with water. The tests are carried out until open cracks are identified. Surface cracks are identified in the base and weld tubes after 120 and 80 cycles respectively. The tubes are then sectioned and subjected to optical microscopy. The causes of failures are thoroughly investigated using Scanning Electron Microscope (SEM). This study reveals that localised heating and cooling causes thermal fatigue which initiates cracks in the tubes.