Experimental and numerical investigation of effect of welding sequence on distortion of stiffened panels

Ship structural components are made of orthogonally stiffened steel panels. These panels are built by welding stiffeners onto the steel plates. The heat-induced distortions resulting from the welding process are of major concern in ship-building industries. These distortions negatively affect many aspects such as productivity, cost of production, manpower requirements, vessel speed, vessel appearance, and most importantly various structural aspects. In this study, low carbon steel large stiffened panels were fabricated using four different welding sequences. Gas metal arc welding as per shipyard’s practice was used to weld these specimens. Initial and final distortions of the panels at various locations on the plate were measured using high-precision coordinate measuring machine. The pattern of welding sequence that needs to be followed for minimizing welding distortion in fabrication of large orthogonally stiffened panels was established. The inherent strain method for evaluating welding distortion using modification proposed by one of the authors in his previous work is used to determine distortion of the stiffened panel. The method uses expressions for inherent strains, based on thermal model of welding supported by correlation with experimental data reported by various investigators. Later elastic FE analysis using shell elements is carried out. This avoids time-consuming elastic-plastic analysis of near-weld region used by other investigators to determine inherent strain. Thus, it makes the whole numerical analysis very fast even for complex structure such as stiffened panel. The values of distortion with four welding sequences used in the stiffened panel were averaged and then compared with the results of numerical analysis using this method. The effect of welding sequence was not incorporated in the numerical analysis, mainly due to lack of experimental data on variation of transverse shrinkage (known as transverse rotation) for incorporation in the expressions of inherent strain. This transverse rotation is mainly responsible for introducing variation in distortion due to different welding sequences. Yet, the experimental results obtained without considering the welding sequence (by averaging the results for different sequences) show good agreement with results of numerical analysis.