In the welding construction of large diameter flange, although there is only one welding joint, X-shaped groove is adopted in consideration of welding deformation and welding quality.First of all, the flange is fixed horizontally on the gantry fixture platform, and then the groove processing. The groove processing first uses the flame to cut, and then uses the grinder to grind. The groove surface is smooth, flat, without obvious grooves, and the groove surface and both sides have no iron oxide, impurities, moisture, oil stains and stratified defects.

Because the thickness of flange is thick, the selection of appropriate welding method directly affects the degree of deformation produced by welding.Large diameter flanges may be deformed after welding if welded improperly.If one side of the X groove is welded first, then the other side is welded;When welding the first side first, the structural rigidity is relatively small and the welding deformation is large. When welding the reverse side, the front weld has been formed and the structural rigidity is greatly increased. At this time, the deformation caused by welding is smaller than that of the front side.Determine the number of welding layers according to the thickness of the welding workpiece and the diameter of the welding rod. In this case, the thickness of the workpiece is 50mm, and it is divided into 10 layers, with 5 layers on each side. The welding is conducted by positive and anti-symmetric welding.
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. Because the welding site is the stress concentration and the flange strength is relatively weak, nondestructive testing must be carried out and the grade requirements must be met.UT inspection level must achieve Ⅰ qualified, or RT level must achieve Ⅱ qualified, according to provisions of JB4730 detection method.