Defect Detection in Weld Joints by Infrared Thermography

The objective of this present paper is to evaluate the effectiveness of infrared thermography (IRT) as a non-contact, fast and reliable non-destructive evaluation procedure for detection and quantification of defects in weld joints. In the present work, a friction stir welded (FSW) joint of two aluminum plates and three 316 LN stain-less steel (SS) weld-joints with lack of penetration (LOP),
lack of fusion (LOF) and tungsten inclusion (TI) defects respectively, were inspected using IRT and digital radio-graphy (DRG). Using active thermography methods, a sub-surface tunnel defect along the weld line was successfully
detected in the FSW joint and its length and width were estimated by suitable pixel calibration. Using lock-in thermography, optimum frequencies were determined for each of the specimens and defect-depths were estimated. Tempe-rature fall of the defect region and defect-free region were monitored as a function of time and it was found that the rate of temperature fall in the former case is slower than that in the latter one. Results from both the tech-niques, i.e., IRT and DRG were found to be in good agree-ment with each other in all the cases. Advantage of IRT is that it provides depth information also.