Micro-cracks in welded joint made of S235JR steel: initiation, detection and critical assessment

Purpose This research elucidates two assumptions regarding the initiation mechanism and practical detectability of micro-cracks in welded joints made of S235JR steel, as well as their often-neglected influence on structural integrity. Design/methodology/approach Research investigates the initiation, detection and influence on structural integrity of small defects, specifically (in most cases neglected) micro-cracks in the weld root, made under controlled laboratory conditions. Consequently, this research investigates two assumptions (through two welding procedures) that can lead to initiation of micro-cracks in welded joint root, while the influence of discovered micro-cracks discovered by microstructural analysis were examined via failure assessment diagram (FAD). Findings Detected micro-cracks are sharp with potential towards further propagation. Examined micro-crack with depth of 0.3 mm lies deep within the safe region of the FAD; its presence and its growth could compromise structural integrity. Research limitations/implications Future research will be focused on more comprehensive investigation on micro-cracks initiation in welded joint with the practical impact on structural integrity assessment of welded structures by using analytical and numerical methods. In addition, the study emphasizes the practical limitations of conventional non-destructive testing (NDT) methods in detecting micro-cracks and emphasizes the need for development and use of more advanced methods. Practical implications This study's findings suggest that the focus regarding structural integrity analysis should shift to more detail characterizing and understanding the mechanisms of micro-crack initiation, detection and propagation, in addition to detecting larger defects. Given that conventional NDT methodologies failed to identify these sub-millimeter defects, the presented approach indicates their importance, especially if located in critical zones in welded joint such as the weld root. Social implications Indirectly, the findings of this study emphasize the necessity of early micro-crack detection, which can directly contribute to the prevention of catastrophic failures along with associated economic consequences. Originality/value The originality of this research lies in the dual experimental and analytical characterization (via FAD) of micro-cracks in structural steel welded joints. These defects can significantly impair overall structural integrity through inevitable crack growth under tensile loading.