1 Large diameter thick-walled seamless steel pipe preheat help with reducing the maximum hardness of the medium carbon steel heat-affected zone and prevent cold cracking, which is the process measures of welding carbon steel, preheating can also improve joint plasticity, reduce welding residual stress. Typically, 35 and 45 steel preheating temperature of 150 ~ 250 ℃ high carbon content or great because of the thickness and stiffness, and crack tendency when the preheating temperature increased to 250 ~ 400 ℃.
2 Preferred alkaline electrode when the electrode conditions permit, it is a good large-diameter thick-walled seamless steel pipe welding.
3 Groove weldment try to open a U-shaped groove-type welding. Casting defects, dig out of the groove shape should be smooth, and its purpose is to reduce the proportion of base metal melt into the weld metal in order to reduce the carbon content of the weld to prevent cracks.
4 Large diameter thick-walled seamless steel pipe welding parameters up to 30% of base metal melted in the proportion of the first layer of weld metal, the first layer of welding should be a small current, slow welding speed to reduce the base metal penetration.
5 Post-weld heat treatment after welding, the best butt immediate stress relief heat treatment, especially for large diameter thick-walled seamless steel pipe weldment, the highly rigid structure, as well as the severe conditions (dynamic load or impact load) work weldment it should be. Eliminate the stress of tempering temperature is 600 ~ 650 ℃. If post-weld stress relief heat treatment should be carried out immediately after the heat treatment.