The welding precautions are: ①In order to reduce the penetration depth on both sides of the groove, fast non-swing welding can be adopted. The middle of the weld can swing slightly, but the swing amplitude should be small. ② When the repair welding workpiece is thicker, the groove section is larger, and multi-layer multi-pass welding is adopted. The welding seam has a large cross-section, and the resulting shrinkage stress is very strong, which is easy to cause weld peeling. Therefore, a reasonable welding sequence is adopted. ③Using short section welding, intermittent welding, scattered welding, and gradual back welding method. Welding short segments, i.e. each segment is about 10 ~ 40 mm . Intermittent welding, that is, stay for a while after welding for a while, and then weld the next weld when the workpiece is cold to 50 to 60 ℃ to prevent heat concentration. Dispersion welding is to weld one part for a period and then to another part to reduce temperature difference and stress. The gradual desoldering method, compared with continuous welding, can greatly reduce the tensile stress peak of the weld, so it is beneficial to prevent weld cracks. ④ Hammer the weld. When hammering the weld, the temperature should be above 400 ℃, and hammer the weld with a small round head .