Abstract: Objective This work aims to investigate the influence mechanism of welding residual stresses on the fracture behavior of cracked P91 steel steam pipelines at different temperatures. Through numerical simulations and experimental verifications, the potential threats of welding residual stresses to pipeline integrity and safe operation are evaluated. Methods The reliability of the finite element model was validated through CT specimen tests. A cracked welded model of the P91 steel steam pipeline was established, and the welding process was simulated using the birth-and-death element technique. The heat transfer module was employed to calculate the temperature field during the welding process. The distribution model of welding stress field was obtained through the thermal mechanical coupling. Results After welding, welding residual stresses were symmetrically distributed along the weld center, decreasing towards both ends along the axial direction. In the thickness direction of the pipeline, they initially increased from the inner layer to the outer layer, then decreased, and finally increased again, with the circumferential stress being the highest and the radial stress the lowest. Upon introducing an initial crack into the pipeline, significant stress concentration occurred at the crack tip region, where tensile stress was observed at the crack center and compressive stress at the crack ends. In the ligament area far from the crack tip, welding residual stresses were barely affected by the crack introduction. As the temperature rose, welding residual stresses gradually decreased, while their distribution patterns remained similar at different temperatures. Welding residual stresses significantly reduced the initiation internal pressure of the P91 pipeline, and the reduction ratio gradually increased with temperature. At 800 ℃, welding residual stresses alone could lead to crack initiation. Welding residual stresses had a significant impact on the stress distribution during crack initiation in the pipeline. Along the thickness direction, the circumferential stress rapidly increased at the crack tip position, reaching a maximum value over a short distance. Along the crack tip direction, the stress near the crack center stabilized and then rapidly decreased, tending to stabilize at the crack end, which might transform into compressive stress at higher temperatures. Conclusion Welding residual stresses reduce the initiation internal pressure of P91 steel pipelines, with a larger reduction ratio at higher temperatures. They facilitate crack initiation at the crack center but inhibit it at the crack ends. Additionally, welding residual stresses decrease the stress required for crack tip initiation, increase the stress gradient in the crack area, and lead to different stress distributions and crack initiation locations in the crack area at various temperatures.