During the welding process of
thin-walled stainless steel pipes, issues such as burn-through, deformation, and susceptibility to rusting of the weld seam often arise due to factors related to welding equipment, welding parameters, and operational details. Below, we'll delve into the welding technology for thin-walled stainless steel pipes.
Adopt the left welding method, ensuring the welding torch moves forward at a uniform speed without jumping up and down. Feed the welding wire along the weld joint, keeping it close to the leading edge of the weld pool. The amount of wire fed depends on the gap and speed. Minimize frequent wire feeding to avoid concave weld seams during flat welding and convex weld seams during vertical welding, adhering to the principle of forming the weld seam in one pass.
Ensure that the end of the welding wire remains within the shielding gas range to prevent oxidation of the hot wire end. Do not allow the welding wire to penetrate the weld pool and disturb the argon gas flow. Use fine welding wire with a diameter ranging from 0.8 to 2.5 millimeters. The welding current for
thin-walled stainless steel pipes should not be too high; it should be sufficient to melt the welding wire, typically ranging from 40 to 100 amps. Use an argon gas flow rate of 8L/min, an 8-millimeter nozzle aperture for the welding torch, and maintain a distance of 5 to 10 millimeters between the nozzle and the workpiece.
Faster welding speeds result in less deformation and produce more aesthetically pleasing weld seams. Despite the inert gas protection during stainless steel pipe welding, contact with oxygen from the air is inevitable. Prolonged exposure of the pipe edges to the air leads to the formation of deeper layers of non-metallic oxides, causing intergranular corrosion and disrupting the continuity of the weld seam structure, resulting in a pronounced brittle interface. Moreover, during stainless steel precision pipe welding, the evaporation of a large amount of alloying elements such as manganese and carbon reduces the mechanical properties of the weld seam. Slower welding speeds lead to increased susceptibility to rusting of the weld seam. By increasing the welding speed, the weld seam quickly exits the heating zone and is rapidly water-cooled, achieving the purpose of refining the weld seam grain size.
Pre-gas flow should be initiated 3 to 5 seconds before arc initiation. Increase the travel speed before arc extinguishing to eliminate arc craters. Post-weld cleaning involves using imported pickling paste, applying it for 20 minutes, brushing off the oxide layer with a wire brush, and rinsing with clean water. For thin-walled stainless steel pipes with low requirements, a wire brush can be used directly, brushing while rinsing.
Careful consideration should also be given to the selection of welding machines. Generally, inverters with both AC and DC capabilities are preferred for their stable current output. Non-consumable tungsten inert gas (TIG) arc welding can be used, characterized by stable combustion, concentrated heat, high arc temperature, high welding productivity, narrow heat-affected zone, and minimal tendencies for welded parts to exhibit stress, deformation, or cracks. It is suitable for welding thin-walled stainless steel pipes and ensures good weld quality. However, tungsten electrodes have limited current-carrying capacity; excessive current should be avoided. Nonetheless, the quality can be guaranteed, and welding thin pipes does not require beveling, making it convenient.
Reasons for Oxidation of Thin-Walled Stainless Steel Pipes
Thin-walled stainless steel pipes rely on a thin but exceptionally robust and dense chromium-rich oxide protective film on their surface to prevent oxygen atoms from penetrating into the steel and obtaining oxidation resistance. However, in some cases, this thin film is continuously damaged. Oxygen atoms from the air or liquid continuously penetrate, or iron atoms from the metal continuously precipitate, forming loose iron oxide, resulting in continuous oxidation of the metal surface. When oxidation occurs on the surface of the steel pipe, oxide accumulation forms. Once it reaches a certain scale, further oxidation slows significantly. So, what are the reasons for the oxidation of thin-walled stainless steel pipes?
Production Process: This is one of the reasons for the oxidation of stainless steel products. From the perspective of production processes and product characteristics, forming a thin oxide film on the product surface is the basic process to avoid oxidation. It is also one of the main features that distinguish stainless steel from other iron and steel products. However, if the production process is insufficient or negligent, resulting in an incomplete and discontinuous oxide film, oxygen in the air directly reacts with some elements in the pipe material, leading to oxidation.
Product Composition Ratio: Some manufacturers, in order to reduce production costs, reduce the proportion of important elements such as chromium and nickel in the product composition and increase the content of other elements, such as carbon. This phenomenon of not strictly following the stainless steel pipe model and product characteristics for composition ratio production not only compromises product quality but also affects the appearance and oxidation resistance of the product. For example, when the chromium content of 304 stainless steel pipes is insufficient, it not only affects the corrosion resistance and formability of the product but also poses quality hazards when applied in industrial settings.
Human Factors: This is also one of the reasons why some consumers frequently encounter product oxidation when using thin-walled stainless steel pipes. Some consumers mishandle products during use and maintenance, especially in industries such as food and chemical equipment, where the probability of human-induced oxidation is higher. To address oxidation caused by human factors, consumers need to possess correct product usage knowledge and regularly carry out reasonable and effective maintenance and care for their stainless steel pipes.
