Abstract: A regular inspection of a boiler in a certain power plant found cracks in the welding seam between the steam drum head and the cylinder section. In order to eliminate safety hazards in the steam drum, a repair plan was developed for on-site repair. Due to the large volume of the steam drum, fast heat dissipation, and high carbon equivalent of the base material, cold cracks are prone to occur during repair welding due to the diffusion of hydrogen in the weld seam, the hardened structure of the weld seam, and the influence of stress. After analysis and research, a heat treatment process combining intermediate frequency induction heating and far-infrared resistance radiation heating is used to complete pre weld preheating, hydrogen removal treatment, and post weld heat treatment, which can effectively prevent the occurrence of cold cracks. After applying the above composite heat treatment process to repair the defects, it passed non-destructive testing, hardness testing, and hydrostatic testing, and passed the special equipment major repair supervision inspection. Through practical application of intermediate frequency induction and resistance radiation composite heat treatment technology, the tooling application is flexible, the heating is uniform, the temperature control is precise, and the heating efficiency is high, effectively reducing the probability of welding residual stress and welding cold cracks. It is suitable for repairing defects in large thick walled pressure equipment on production sites.