Selection of welding materials In low-temperature environments, low-hydrogen or ultra-low-hydrogen welding materials should be selected as much as possible, and baking and heat preservation measures should be strictly implemented for the welding materials.
.Pre-welding protection
Set up a protective shed in the welding operation area to form a relatively closed space in the welding area and reduce heat loss. If the protective shed is unconditionally set up, other effective measures should be taken to protect the welding area. During gas shielded welding, corresponding measures should also be taken to insulate the welding gas cylinder.
.Welding quality control
Preheating and interpass temperature. The preheating temperature in low temperature environment should be slightly higher than the welding preheating temperature at normal temperature. The heating area is the base metal within the welding zone of the component that is greater than or equal to twice the thickness of the steel plate in all directions and not less than the range. The temperature between welding layers is not lower than Preheating temperature or the minimum temperature ℃ specified by the standard () (whichever is higher). Increase the heat input during positioning welding. Appropriately increase the heat input of positioning welding, increase the weld section and length, and adopt the same preheating conditions as the formal welding. Do not arc on the base metal other than the groove. The arc crater must be filled when the arc is extinguished. You can Effectively reduce shrinkage cracks caused by positioning welding. Use reasonable welding methods. Try to use narrow swing, multi-layer and multi-pass welding, and strictly control the inter-layer temperature. Heat and insulation after welding. Post-heat insulation treatment of the welded joints in time after welding can facilitate the diffusion of hydrogen and prevent cold cracks caused by too fast cooling. At the same time, appropriate post-heating temperature can also appropriately reduce the preheating temperature.
In short, before low-temperature welding construction of steel structures, welding process qualification tests must be conducted based on actual conditions. If necessary, low-temperature weldability tests should be conducted for specific steel types, and suitable welding process instructions should be produced to guide actual welding. In addition, in low-temperature environments, sufficient attention should be paid to the adverse effects of welder operations. Generally, the ambient temperature should not be lower than ℃.
Thick steel plate welding technology
Medium and thick steel plates are widely used in building steel structures. For example, the rolled steel wing plates used in the Beijing New Poly Building project have a thickness of up to 100%, and the maximum thickness of the steel used in the National Stadium (Bird's Nest) project is Da. A large number of steel structure projects use thick steel plates, which promotes the development of thick steel plate welding technology and also enriches the scope of construction steel.
The key to welding thick steel plates is to prevent cracks and reduce deformation caused by welding. The following points should be mainly considered:
Select a reasonable groove form. If you try to use double or grooved grooves, if you can only weld on one side, you should use small angles and narrow gap grooves on the premise of ensuring welding penetration to reduce welding shrinkage, improve work efficiency, and reduce welding residual stress. Reasonable preheating and interpass temperature. Post heat and insulation treatment.
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Low temperature welding construction technology of steel structure