Corrosion Thickness Characterization in Steels by Means of Active Thermography

The present work concerns the study of distributed defects on metal surfaces. A typical situation is represented by corrosion due to environmental effect, for example in pipings. In this case, the detection of both presence and corrosion amount inside piping is difficult and often requires the use of non-destructive techniques. Aim of this work is the feasibility analysis of active thermography for non-destructive detection and quantification of corrosion in steel sheets. In particular, the present work aims at developing a data processing technique for thermal results obtained on steel sound and corroder sheets by means of a laser thermal investigation. Both pulsed and lock in active thermography techniques are explored, in transmission configuration. The influence of excitation parameters on damage detection and quantification performance was also investigated. To this aim different samples of specimens were obtained with increasing corrosion damage, by means of keeping the specimens in a saline cell for increasing time intervals. For all the investigations, the reference signal consisted in the sound sheet thermal response. Data processing allowed to relate frequency and time parameters of the thermal response to the corrosion level. The entity of corrosion was also compared to the thickness specimen variation obtained by means of a metallographic optical microscope.