Socket welding generally inserts the pipe into the flange for welding. Butt welding uses the butt welding flange to butt weld the pipe and the butt surface. The socket welding joint cannot be radiographically inspected, but the butt welding can be used, so the inspection requirements for the welding joint are required. High butt welded flanges are recommended. Generally, the requirements for butt welding are higher than those for socket welding, and the quality after welding is also good, but the detection methods are relatively strict. Butt welding should do radiographic inspection, and socket welding should do magnetic particle or penetrant inspection (like carbon steel as magnetic particle, stainless steel as penetrant). If the fluid in the pipeline does not have high requirements for welding, it is recommended to use socket welding, which is convenient for detection. The connection form of socket welding is mainly used for welding small diameter valves and pipes, pipe fittings and pipes. Small-diameter pipes generally have thinner walls, are prone to misalignment and ablation, and are more difficult to weld, so they are more suitable for socket welding. In addition, the socket of socket welding has a reinforcing effect, so it is often used under high pressure. However, socket welding also has its shortcomings. One is that the stress condition after welding is not good, the welding is prone to incomplete penetration, and there are gaps in the pipe system. Therefore, it is not suitable for the pipeline system used for crevice corrosion-sensitive media and the pipeline system with high cleanliness requirements. Use socket welding. In addition, for ultra-high pressure pipelines, even small-diameter pipelines have a large wall thickness, and socket welding can be avoided as far as possible if they can be connected by butt welding. In short, socket welds form fillet welds and butt welds form butt welds. The butt joint is better than the socket joint from the strength and stress condition of the welding seam, so the butt joint should be adopted in the occasions with high pressure level and bad service conditions.
Pipe flange welding includes flat welding, butt welding and multi-pass welding flanges.
1. Select the appropriate flange material according to the material of the pipeline, such as stainless steel pipeline is definitely not allowed to choose flanges such as carbon steel; 2. Select the appropriate flange according to the nominal diameter (DN) of the pipeline and the nominal pressure (PN) of each section of the entire pipeline system. At present, the international pipe flange basically adopts the American standard system and the European standard system; 3. Select the flange structure according to the specific working conditions: such as flat welding with neck, looper flange, etc., the sealing surface forms include convex surface, full plane, concave and convex surface, etc. 4. For non-standard parts, it should be designed and manufactured according to the flange specification design procedure.