## 4 Results
### Effect of Fin Size on Residual Stress and Deformation  
Owing to the significant temperature difference on both sides of the connecting fins, they were subjected to significant thermal stress. Owing to the geometric discontinuity caused by structural factors and material discontinuity caused by welding seam factors, significant stress concentration occurred at the connecting fins. In practical engineering, due to various factors, such as size and construction, the size of the connecting fins varied, making it difficult to estimate the distribution of welding residual stress and prone to cracking and failure during operation. Therefore, finite element simulations were conducted on connection fin models with different widths and thicknesses to elucidate the influence of connection fin size on welding residual stress. The models used were consistent with the previous text, except for the width and thickness dimensions of the connecting fins. The stress and deformation curves distributed along the path under different connecting fin thicknesses are shown in Figure 9. As the thickness of the fins gradually increased, the ranges of stress reaching yield on the welded structure were 78.66, 77.55, 75.72, and 75.22 mm, respectively (Figure 9a), which means that, as the thickness of the connecting fins increased, the yield range decreased. The thickness of the connecting fins had little effect on the distribution and amplitude of longitudinal stress. Different fin thicknesses of 6, 8, 10, and 12 mm corresponded to maximum longitudinal stress of 417.74, 413.96, 408.21, and 406.31 MPa (Figure 9b). When the thicknesses of the fins were 6, 8, and 10 mm, the distribution of deflection deformation in the longitudinal path showed a trend of high in the middle and low on both sides. However, when the thickness further increased to 12 mm, the deflection deformation of the flue-side wall structure significantly decreased, and the distribution in the longitudinal path tended to be flat. In addition, the maximum value of deflection deformation on the structure showed a significant downward trend with the increase in fin thickness (Figure 9c). The stress and deformation curves along the path under different connection fin widths are shown in Figure 10. When the widths were 10, 17.5, 30, 50, and 70 mm, the  
Figure 8: Stress and deformation distribution curves along the path under different welding rates: (**a**) equivalent von Mises stress, (**b**) longitudinal stress, and (**c**) deflection. Figure 9: Stress and deformation distribution curves along the path with different fin thicknesses: (**a**) equivalent von Mises stress, (**b**) longitudinal stress, and (**c**) deflection. ranges of welding residual stress on the structure reaching material yield were 66.643, 77.55, 91.293, 110.225, and 120.582 mm, respectively (Figure 10a). As the width of the connecting fins increased, the range within which the structure reached yield also increased. When the fin width was narrow, all the connecting fins yielded after welding, and as the fin width increased to ~70 mm, the middle part of the connecting fins away from the weld no longer yielded. After welding, all the connecting fins reached yield. Therefore, as the width of the connecting fins increased, the range of the structure reaching yield also increased. The maximum longitudinal stresses on welded structures with different fin widths of 10, 17.5, 30, 50, and 70 mm were 413.511, 413.96, 414.441, 417.206, and 412.77 MPa, respectively (Figure 10b). As the fin width increased, the maximum longitudinal stress did not change much and was slightly higher than the yield strength of the material. When the fin widths were 10, 17.5, 30, 50, and 70 mm, the maximum deflection deformations on the structure were 3.832, 1.624, 2.011, 3.521, and 26.92 mm, respectively (Figure 10c). It can be seen that, under the condition of a fin thickness of 8 mm, the structural deflection deformation was relatively small when the fin width was between 10 and 50 mm.