Welding Process of 12Cr1MoVG High Pressure Boiler Pipe

12Cr1MoVG belongs to pearlitic low alloy heat-resistant steel, which has high Cr content and high thermal strength and fatigue strength at 500~550 ℃. 1、 Welding method During the welding of alloy pipes of high-pressure boiler, the quality of the backing weld is required to be high, which requires not only the weld penetration and smooth back without defects, but also the back of the weld without slag or less slag, otherwise the safe operation of the equipment will be affected. Therefore, manual argon tungsten arc welding is used for backing, manual arc welding for filling and covering. 2、 Selection of welding materials Manual argon tungsten arc welding wire: ER50-6 wire, wire diameter φ 2.5mm。 Manual arc welding electrode: R307 (E5515-B2) electrode, diameter φ 3.2mm、 φ 4mm。 3、 Preheating before welding Preheating can slow down the cooling rate of the weld and heat affected zone, help avoid the generation of hardened structure, help the escape of hydrogen in the welding zone, and prevent welding cracks. Due to the high carbon content and alloy element content of 12Cr1MoV steel, the preheating temperature shall be 200~300 ℃. The preheating area shall be centered on the weld and at least 100mm on both sides. During the whole welding process, the interpass temperature shall not be lower than the preheating temperature. 4、 Welding operation For the welding of 12Cr1MoVG steel, not only the welding specification parameters should be strictly controlled, but also the welding operation has a crucial impact on the joint quality. The welding procedure is as follows: a. Backing by argon arc welding: fix the pipe fittings horizontally, use short arc during welding, and make the welding gun as vertical as possible to the workpiece surface, which is conducive to the protection of the welding pool by argon. The welding gun and welding wire can swing laterally to ensure the penetration on both sides of the groove. At the same time, the temperature of the molten pool shall be controlled to prevent weld penetration and overlap defects. At the joint, the arc crater shall be polished with an angle grinder to remove the arc stopping cracks, air holes and other welding defects at the arc crater, and then continue to conduct arc striking welding. b. During arc welding filling, short arc welding shall be adopted, and the heat input shall not be too large. If long arc welding is adopted, problems such as unstable arc burning, shallow penetration, large metal spatter and increased alloy element burning will occur, and defects such as undercut and incomplete penetration will easily occur. At the same time, harmful gases such as N 2 and O 2 in the air are easy to enter the molten pool, forming porosity defects in the weld. Small crescent shaped electrode can be used during welding. Stay at both sides of the groove for 0.5~1s. The welding slag must be thoroughly cleaned between the welding layers. When welding defects such as air holes are found, the welding defects shall be removed with an angle grinder. The crater must be filled during arc extinguishing to avoid crater cracks. Joints between layers shall be staggered without overlap. c. When covering the surface with electric arc welding, the welding current shall be slightly less than the filling, the correct electrode angle shall be selected, and the electrode shall be uniformly transported to prevent undercut defects at the edge of the groove. The weld reinforcement shall be controlled within 1~3mm to avoid stress concentration of the joint in use. 5、 Post weld heat treatment After welding, stress relief heat treatment shall be carried out to heat the welded junction as a whole to 720-760 ℃. After 1~2h of constant temperature, heat insulation materials shall be used to cover the weld and the near seam area for heat preservation, so that the joint can be slowly cooled to room temperature. The purpose of heat treatment is to eliminate or reduce the hardening structure in the affected area, increase the plasticity and toughness, effectively reduce the welding residual stress, and at the same time, it is conducive to the escape of diffusing hydrogen, thus reducing the tendency of cold cracks.铜焊丝,Copper Welding Rods,铝焊丝,aluminium welding wire,镍焊条,Nickel electrode,药皮焊条,Flux Coated Brazing Welding Rods