Evaluation of material properties and hoop residual stress in proximity welded sections of S355 steel

Abstract This study investigates the thermal distribution and its effect on the material characteristics and the distribution of hoop residual stresses in welds with varying proximity distances, made from S355 G14 + N steel circular hollow sections. Girth welds have been shown to be performed in close proximity in structures subjected to dynamic loading, and these welds can have residual stresses that can have a significant effect on fatigue strength and overall structural integrity. It is known that the thermal effects from the welding process can have different effects on the residual stress levels as well as the materials microstructure and mechanical properties depending on the proximity. This study aims to evaluate the material characteristics and residual stress levels in the weld proximity regions and their potential impact on fatigue performance. Three hollow cylindrical sections, each with a diameter of 219.1 mm, were welded at proximity distances of 5 mm, 15 mm, and 50 mm for analysis, thermal camera to verify the magnitude of heat distribution. In order to investigate the microstructure and mechanical characteristics across the proximity welds hardness tests and scanning electron microscope (SEM) is employed. Subsequently, by applying the sectioning method three strips were cut from each section and analyzed. The amount of residual strains relieved was used as a measure to evaluate the level of residual stresses. Strain gauges were employed to measure the surface hoop residual stresses relived during the extraction of the strip specimens. The results demonstrated that proximity distance and welding procedure have a significant influence on the distribution of residual stresses. The residual stresses measured in the extracted samples were consistent with those observed in full girth welds from previous studies, showing tensile stresses in the weld, and compressive stresses on each side of the weld. This stress profile remained consistent across the different proximity distances. In addition, at a proximity distance of 50 mm, compressive residual stresses increased significantly in the proximity region. Notably, the results are showing higher tensile stresses in the heat affected zone on the side of the last weld near the final weld bead raising concerns about the weld’s integrity under cyclic loading. These findings suggest that controlling thermal cycles and weld sequence is crucial for optimizing residual stress distribution and improving the fatigue performance of girth-welded structures with welds at close proximity.