Welding process and method of large diameter flange
In the welding construction of large-diameter flange, although there is only one weld junction, X-shaped groove is adopted in consideration of welding deformation and welding quality.
Asymmetric x-groove
Firstly, fix the annular blank horizontally on the gantry fixture platform, and then conduct groove processing. The groove processing is first cut by flame and then ground by grinder. The groove surface is required to be smooth, flat and free of obvious grooves, and there are no defects such as iron oxide, impurities, moisture, oil stains and delamination on on the groove surface and both sides.
Due to the thick thickness of the blank, the selection of appropriate welding method directly affects the deformation degree caused by welding. Select manual welding for symmetrical welding on both sides.
If the large diameter flange is not welded properly, it may still produce post welding deformation.
For example, weld one side of groove x before welding the other side; When the first side is welded first, the structural rigidity is relatively small and the welding deformation is large. When the reverse side is welded, the weld on the front side has been formed and the structural rigidity is greatly increased. At this time, the deformation caused by welding is smaller than that on the front side. Although the two deformation directions are opposite, they can not completely offset, and the deformation direction of the first side is still retained at the end.
Welding sequence of large diameter flange
The number of welding layers is determined according to the thickness of the welding workpiece and the diameter of the welding rod. In this example, the workpiece is 50mm thick and is divided into 10 layers with 5 layers on each side. The welding adopts positive and negative symmetrical welding. After each layer is welded, hammer the weld several times, and remove the tooling fixture after the weld is completely cooled to eliminate the welding stress as much as possible.
After the welding of large-diameter flange is completed, a comprehensive RT or UT inspection shall be carried out according to the requirements of JN4700. Since the welding part is the part with concentrated stress and weak flange strength, NDT must be carried out and must meet the grade requirements. UT inspection must reach level I qualification, or RT must reach level II qualification, and the detection method shall be carried out according to JB4730.
Source: China Flanges Manufacturer – Yaang Pipe Industry (www.pipelinedubai.com)