Control of welding deformation of demineralized storage tanks in nuclear power plants

1 Overview

In the construction of civil nuclear power, most of the demineralized water Storage Tanks adopt on-site prefabrication and assembly methods, which are basically vertical cylindrical tank structures. The storage tank is mainly composed of a bottom plate, a wall plate and a vault. It has the characteristics of large volume, thin plate and large welding workload, and welding stress and welding deformation are inevitable during the welding process. If the welding deformation is not well controlled during the on-site construction process, it will not only affect the assembly, but will not be put into use in severe cases. Therefore, it is necessary to formulate a suitable welding construction plan and take effective deformation control measures to ensure the welding quality.

2. Deformation analysis and control measures

(1) Deformation analysis

1 Because the plate of the demineralized water storage tank is thin, its own steel is small, the area is large, and it is also affected by the ambient temperature.

2 The weld length is long, and there are many T-shaped welded joints, which are prone to wave deformation (especially when the pair of spokes in the bottom plate are welded).

3 The anti-deformation amount is not reserved, and the effective measures for reducing the stress are not taken after the welding, or the welding process is improperly operated, and the rigid fixed member is removed in advance.

(2) Control measures

1 In the welding process, it is necessary to monitor the temperature and humidity of the environment, and do the relevant cold and shading measures to minimize the impact of the ambient temperature on the deformation.

2 rigid fixing method to reduce welding deformation. After the welding is completed, try not to remove the rigid fixing parts urgently, and then remove them after 24 hours.

3 When welding the T-shaped weld, reserve 150mm on the short side of the weld, and weld it when the long weld is welded.

4 For the circumferential welds, it is recommended to send 4 welders to weld at the same time using the symmetrical segmented jump welding method and the segmental back-welding method. The consistency and synchronization of the welding must be maintained.

5 reserve anti-deformation.

6 Strictly control the welding heat input, using small welding parameters and fast welding.

7 After the welding is completed, it is recommended to use an air hammer or a hammer to hammer the weld and the heat affected zone to reduce the welding stress.

For more details, please refer to the attachment or the contents of the 20th issue of Metalworking (Hot Processing).