<p>This paper presents a recent investigation on the primary plus secondary local PWHT (PS-PWHT) method in mitigating residual stresses of large-scale pressure vessels. Using the finite element method, this study analyzes the effects of structural dimensions and materials on residual stress relief during PS-PWHT, with an emphasis on inner surface stresses. The results demonstrate that the effectiveness of residual stress relief achieved by the PS-PWHT method depends not only on key process parameters but also on radius, wall thickness, and materials. During the primary heating stage, only one heated band is applied. The residual stress distribution on the inner surface is related to the material's constraint and strength. Higher constraint (i.e., girth welds with smaller diameter and greater wall thickness) and strength (i.e., 12Cr2Mo1V girth welds) lead to less waist‑shrinking deformation caused by cooling contraction, resulting in a smaller change in residual stress compared to the as‑welded condition. In the secondary heating stage, the reverse deformation induced by two secondary heating bands is influenced by the radius, wall thickness, and thermal expansion coefficient. Larger values of radius, wall thickness, and thermal expansion coefficient (e.g., TP 347 girth welds) result in greater reverse deformation, which in turn leads to a lower residual stress distribution on the inner surface. Therefore, the PS‑PWHT&#xa0;method achieves superior residual stress relief in girth welds with larger diameters, greater wall thicknesses, and higher thermal expansion coefficient of material. These findings provide theoretical guidance for mitigating welding residual stresses in large-scale pressure vessels through the PS-PWHT method.</p>