Welding deformation and control correction of steel structure

In the welding process of welded steel pipe, the welding stress and deformation are caused by local uneven heating. The weld metal and the heating zone near the weld will expand. If the cooler metal around wants to prevent this expansion, it will produce compressive stress and plastic shrinkage deformation, resulting in transverse and longitudinal shrinkage. The shrinkage in these two directions will lead to various deformations of the welding structure.

Measures to prevent and reduce structural deformation:

1. Reduce the cross-sectional area of the weld: on the premise of obtaining a defect free weld, use a smaller groove size.

2. For steel with yield strength less than 345mpa and weak hardening ability, small heat input shall be adopted, preheating and inter layer temperature shall be appropriately reduced, and welding method with less heat input shall be preferred

3. Multi layer welding is adopted for thick plate welding

4. Double sided symmetrical groove shall be adopted for double-sided welding, and the welding sequence symmetrical to the component shall be adopted for multi-layer welding

5. When welding T-shaped joints with large thickness, beveled fillet butt welds shall be used

6. The deformation prevention method before welding is used to control the angular deformation after welding. It is a common method to basically offset the weldment in advance

7. Rigid fixation method: also known as mandatory method. In actual production, the deformation of components with high stiffness after welding is generally small, while the stiffness of components with low stiffness can be strengthened before welding, and the deformation after welding can be reduced accordingly. Using this method, the fixture and support need to be removed after welding cooling. Common methods include fixture method, support method, mould method, temporary fixation method and positioning welding method.

8. Hammer weld method: this method is mainly applicable to welding thin plates. When the thin plate weld and its heat affected zone are not completely cooled, hammer the area immediately and knock the thick plate with an air gun

9. Arrange the welds reasonably and reduce the number of welds. In addition to avoiding dense welds, make the welds symmetrical to the neutral axis of the member

10. Correctly select the welding sequence. When there are butt welds and fillet welds, the butt welds shall be welded first and then the fillet welds. The cross and T-shaped welds shall be in the correct sequence to avoid stress concentration and ensure the welding quality. The welding symmetrical to the neutral axis of the whole steel structure shall be adopted, and the two-stage welding from the middle phase is adopted, which is very beneficial to reducing the deformation, For the welding of important parts with high strength, the joint shall shrink freely as far as possible without constraints