This paper highlights the modeling, simulation and detection of deposited scales in boiler tubes by Pulsed Thermography (PT). A novel data analysis method, based on variations of slopes in Temperature-Time profiles approach has been adopted, to estimate subsurface scale thickness and material loss in the tubes. The slopes are obtained for different pixels in the field of view of the captured image sequence during transient heating of the boiler tube. Relative thickness variations due to material loss and the deposited scales of boiler tube have been estimated from the calculated slopes. Experimental results are presented in support.