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When welding low-carbon steel structures under severe winter conditions, the cooling rate of the welded joint is fast, which increases the tendency of cracks. Especially the first weld of thick structures is prone to cracking. For this reason, the following process measures must be taken: 1) Preheat before welding, and strictly maintain the interlayer temperature not lower than the preheating temperature during the welding process. 2) Use low hydrogen or ultra-low hydrogen welding materials. 3) When positioning welding, increase the welding current, slow down the welding speed, appropriately increase the cross-sectional area and length of the positioning weld, and preheat if necessary. 4) The entire weld should be welded continuously as much as possible to avoid interruption. 5) Arc ignition should not be carried out on the base material other than the groove surface, and the arc crater must be filled when the arc is extinguished. 6) Try not to bend plates, straighten and assemble weldments under low temperature conditions. The preheating temperatures for low-temperature welding of various metal structures are shown in Table 4. The preheating temperatures for low-temperature welding of pipes and pressure vessels are shown in Table 5. Table 4 Preheating temperature for low-temperature welding of low-carbon steel metal structures. Weldment thickness (mm). Preheating temperature at various temperatures is <3031~5051~70 and not less than -30℃. No preheating is required. ； Preheating when the temperature is lower than -30℃ 100~150℃ No preheating when the temperature is lower than -10℃ ； Preheat when it is lower than -10℃, 100~150℃, no preheat when it is not lower than 0℃ ； Preheat 100~150°C when lower than 0°C Table 5 Preheating temperature for low-temperature welding of mild steel pipes and pressure vessels Weldment thickness (mm) Preheating temperature at various temperatures <1617~3031~4041~50 No preheating when not lower than -30°C ； Preheating when the temperature is lower than -30℃ 100~150℃ No preheating when the temperature is lower than -20℃ ； Preheat when the temperature is lower than -20℃. 100~150℃. No preheating when the temperature is lower than -10℃. ； Preheat when it is lower than -10℃, 100~150℃, no preheat when it is not lower than 0℃ ； Preheat 100~150 when it is lower than 0℃℃