Infrared thermography-based studies on hydrotesting of stainless steel pressure vessels

Non-destructive evaluation is essential for the safe and uninterrupted operation of pressure vessels. This study reports on infrared thermography-based online hydrotesting of three AISI type 304 stainless steel pressure vessels with simulated defects of 1.8 mm, 2.2 mm and 2.5 mm depths. The surface temperature rise of the defect and defect-free regions are remotely monitored using an infrared camera. It is observed that the temperature rise of the defect region is much higher compared to that of the defect-free regions and the normalised temperature difference monotonically increases with defect depth due to the higher stress concentration-induced faster rate of deformation. The rate of increase of the normalised temperature difference rapidly increases with defect depth and the rate is found to be linearly correlated with the normalised stress difference between the defect and defect-free regions. The ring-like hot-spot observed in the defect regions in the infrared images, prior to failure, corresponds to the circular morphology of the fabricated defects, and the circumference of the circular defects is identified as the most probable location for crack initiation. Contrast enhancement of the acquired infrared images is achieved using image processing algorithms. This study shows that infrared thermography can be effectively used for online monitoring of growing defects during hydrotesting of pressure vessels.