Hot-Spot Stress Evaluation of Transformer Tank Welded Joints Using Finite Element Analysis

Welded joints constitute one of the most widely employed methods in the assembly of machine components. Owing to the presence of structural discontinuities, however, these joints are susceptible to stress concentrations in the welded regions, which renders the preservation of structural integrity a matter of critical importance. In particular, weld toes, where pronounced local stresses are observed, represent the most common initiation sites for fatigue cracks. In this study, the fatigue strength of weld seams located between the sidewalls and the bottom plate of the transformer tank was investigated using structural hot-spot stress approach, compliance with the recommendations of the International Institute of Welding (IIW). The hot-spot stress values, derived from maximum principal stresses, were subsequently compared against the S-N curves specified by IIW. The fatigue life assessment of the weld seams was carried out based on the FAT-90 classification, taking into account both the steel material and the employed welding technique. According to the IIW standard, the allowable stress limit corresponding to 30,000 loading cycles was calculated to be approximately 380 MPa, whereas the computed hot-spot stress at the critical weld region was 254 MPa, which is about 33% lower than the permissible limit. These findings confirm that the analyzed welded joints possess adequate fatigue resistance and satisfy the safety and durability requirements defined by the governing design standards.