What are the details of the welding forming technology for thin-walled stainless steel pipes

Thin-walled stainless steel pipes are prone to problems such as burn-through, deformation, and rust during welding. These issues stem from the welding equipment, welding parameters, and operational details.

1. For thin-walled stainless steel pipes, the left-hand welding method is used. The welding torch advances at a constant speed, maintaining a steady vertical movement. The welding wire is added along the weld joint, close to the weld edge, from the leading edge of the molten pool. The amount added depends on the gap and speed. Add the wire frequently but in small amounts to avoid concave welds during flat welding and convex welds during overhead welding. The principle is to form the weld in one pass.

2. The tip of the welding wire must always be within the argon gas protection zone to prevent oxidation of the red-hot tip. The welding wire should not be inserted into the molten pool to disrupt the argon gas flow. The welding wire must be thin, with a diameter of 0.8–2.5 mm. The welding current for thin-walled stainless steel pipes should not be too high, just enough to melt the welding wire, generally between 40–100 A. Argon flow rate: 8 L/min; welding torch nozzle diameter: 8 mm; nozzle-to-workpiece distance: 5-10 mm.

3. The faster the welding speed of thin-walled stainless steel pipes, the better, as deformation will be smaller and the weld seam will be more aesthetically pleasing. Even with inert gas protection, thin-walled stainless steel welded pipes inevitably come into contact with oxygen in the air. The longer the edges of the heated tube blank are exposed to air, the deeper layers will develop non-metallic oxides, causing intergranular corrosion, thus disrupting the continuity of the weld seam and forming a brittle interface. Furthermore, a large amount of manganese, carbon, and other alloying elements burn off and evaporate during the welding process of thin-walled stainless steel precision pipes, reducing the mechanical properties of the weld seam. Therefore, it can be concluded that the slower the welding speed, the more prone the weld seam is to rust. By increasing the welding speed, the weld seam of the thin-walled stainless steel pipe is quickly removed from the heating zone, and rapid water cooling is applied to refine the weld grains.

4. Pre-send gas for 3-5 seconds before arc ignition for thin-walled stainless steel pipes. Before extinguishing the arc, increase the travel speed first, then extinguish the arc to eliminate the crater. For post-weld cleaning of thin-walled stainless steel pipes, use imported pickling paste. After applying, wait 20 minutes, then brush off the oxide scale with a wire brush and rinse with clean water. For thin-walled stainless steel pipes with lower requirements, a wire brush can be used directly, brushing and rinsing simultaneously.

5. The welding machine used for processing thin-walled stainless steel pipes is also important. Generally, an inverter AC/DC welding machine is chosen because the current is relatively stable. A non-consumable electrode argon arc welding arc can be used, which offers stable combustion, concentrated heat, high arc column temperature, high welding production efficiency, narrow heat-affected zone, and low stress, deformation, and cracking tendency in the welded parts. It is suitable for welding thin-walled stainless steel pipes and can obtain good ends, ensuring mechanical properties. However, the tungsten electrode has a limited current-carrying capacity, so the current cannot be too high, but the quality is guaranteed, and beveling is not required when welding thin-walled stainless steel pipes, which is very convenient.

The above covers the welding and forming technology for thin-walled stainless steel pipes. When welding thin-walled stainless steel pipes, the left-hand welding method should be used, the welding wire tip should always be within the argon gas protection range, the welding speed should be increased, the current should not be too high, the weld should be cooled with water, gas should be supplied 3-5 seconds in advance when igniting the arc, and a stable inverter AC/DC welding machine should be selected. By following these steps, the thin-walled stainless steel pipe will not deform during the welding process.