目前，多尺度焊接残余应力释放行为对承压设备疲劳失效的影响机制尚无统一定论。本工作以SAF 2205双相不锈钢焊接接头为研究对象，采用实验和模拟相结合的方法，揭示了多尺度焊接残余应力随循环周次的释放行为，提出了多尺度焊接残余应力释放预测模型，阐明了焊接残余应力释放对疲劳损伤行为的影响机制。结果表明，低周疲劳时，焊接残余应力完全释放并转化为塑性变形，显著提升了焊缝的应变幅值，导致焊缝失效对应的应力幅范围变宽。高周疲劳时，试样中心表面高水平焊接残余应力导致裂纹启裂位置由试样侧面转移至中心表面；晶界奥氏体与周围晶粒显著的力学性能差异及焊接残余应力拉-压属性不匹配导致的牵制作用导致裂纹萌生寿命降低。基于上述研究，建立了考虑焊接残余应力释放的疲劳寿命预测模型，预测结果与实验数据吻合较好，误差小于20%。

Recently, in the manufacturing industry, advancements toward high-parameter and lightweight designs has resulted in an increasing prominence on the influence of multiscale residual stress on the fatigue failure of pressure equipment. However, there is no unified conclusion on the influence of multiscale welding residual stress relaxation behavior on the fatigue failure of pressure equipment. This could be due to the following factors: (i) the multiscale coupling characteristics of residual stress, (ii) complexity of material microstructure, and (iii) dynamic evolution of stress relaxation behavior under cyclic loading. These factors hinder traditional fatigue life prediction methods to accurately evaluate the service performance of welded structures with residual stress. Therefore, this study utilizes SAF 2205 duplex stainless steel welded joints and reveals the relaxation behavior of multiscale residual stresses with the number of fatigue cycles. Additionally, this study proposes a predictive model for multiscale residual stress relaxation and clarifies the influence mechanism of residual stress relaxation on fatigue damage behavior. The results show that under low-cycle fatigue conditions, residual stresses are completely relaxed and converted into plastic deformation, which markedly increases the strain amplitude of the weld and broadens the stress amplitude range leading to weld fracture. Under high-cycle fatigue conditions, high-level residual stress shifts the crack initiation site from the specimen side surface to the specimen central surface. The substantial mechanical property difference between grain boundary austenite and surrounding grains, together with the constraint effect induced by the mismatch between the tensile and compressive attributes of residual stresses reduces the crack initiation life. Based on the above research, this study establishes a fatigue life prediction model considering residual stress relaxation. The results agree well with the experimental data, with a prediction error of less than 20%.