Pressure vessel plays an extremely crucial role In industrial production,. Whether it is reactors in chemical production or boilers and storage tanks in the energy sector, the safe operation of pressure vessels is directly related to production efficiency, product quality, and personnel safety. Welding technology, as the core process in the manufacturing of pressure vessels, is of paramount importance in terms of both quality and efficiency. Among various welding methods, submerged arc welding (SAW), with its unique advantages, has become an indispensable process choice in the manufacturing of pressure vessels.
Submerged arc welding, also known as submerged arc automatic welding or flux-cored automatic arc welding, is a process where the arc burns under a layer of flux for welding. The core principle involves feeding the welding wire through a conductive nozzle into the flux layer, where the arc, covered by the flux, melts the wire and the base metal to form a weld seam. It is a commonly used welding method in the manufacturing of pressure vessels.
Submerged arc welding is a method where the arc burns under a layer of flux for welding. Its full name is submerged arc automatic welding, also referred to as flux-cored automatic arc welding. During the welding process, the welding wire is fed through a conductive nozzle into the flux layer, where the arc burns under the flux cover, melting the wire and the base metal to form a weld seam. The flux plays a vital role in the welding process. It not only isolates the air to prevent oxidation and nitriding of the weld seam but also, through the slag cover, slows down the cooling of the weld seam, reducing welding defects.
High Production Efficiency: The high production efficiency of submerged arc welding is mainly due to two reasons. On one hand, the reduction in the length of the welding wire's electrical conductivity increases the current and current density, significantly enhancing the arc's penetration and wire deposition efficiency. For example, without beveling, a single-sided penetration of up to 20mm can be achieved. On the other hand, the insulating effect of the flux and slag reduces heat radiation loss from the arc and minimizes spatter. Although there is an increase in heat loss used to melt the flux, the overall thermal efficiency is still greatly improved.
High Weld Seam Quality: The slag provides excellent air isolation, offering good protection for the weld seam. Moreover, welding parameters can be automatically regulated to maintain stability, requiring less skill from the welder. The weld seam composition is stable, and the mechanical properties are good. This enables submerged arc welding to meet the strict requirements for the strength, toughness, and density of welded joints in pressure vessels.
Good Working Conditions: Compared to manual welding, submerged arc welding significantly reduces the physical labor intensity of the operators. More importantly, it eliminates arc radiation, a unique advantage of submerged arc welding, providing a safer and more comfortable working environment for workers.
Submerged arc welding is widely used in the manufacturing of important steel structures such as pressure vessels, pipe sections, and box beams. It is particularly prevalent in industries like shipbuilding, boilers, chemical containers, bridges, lifting machinery, metallurgical machinery manufacturing, marine structures, and nuclear power equipment. Additionally, it is suitable for welding special materials like nickel-based and copper-based alloys, as well as for cladding wear-resistant and corrosion-resistant alloys.
Pressure vessels have extremely high requirements for welding quality, and submerged arc welding flux plays a key role in this process.
In the welding process of pressure vessels, the role of submerged arc welding flux cannot be underestimated. The flux forms a slag cover during welding, isolating the air and slowing down the cooling of the weld seam. This characteristic is especially suitable for welding materials commonly used in pressure vessels, such as low-alloy steel and stainless steel. For example, in the manufacturing of containers for flammable and explosive media, submerged arc welding flux can effectively reduce defects like porosity and slag inclusion, enhancing the density of the weld seam.
The strictness of welding processes in the pressure vessel industry has driven the development of submerged arc welding flux towards specialization. Taking the GB/T 5117 standard as an example, for welding pressure vessel steels (such as Q345R and SA516), it is necessary to select matching sintered flux to ensure that the mechanical properties meet the standards. In actual production, the collaborative design of flux and welding wire is particularly critical. Acidic flux is suitable for ordinary carbon steel containers, while alkaline flux is used for high-strength steel or low-temperature service environments, achieving a balance between toughness and strength through compositional control.
The physical properties of flux directly affect penetration and weld formation. By adjusting the particle size and alkalinity, the welding requirements for pressure vessel shells of different thicknesses can be met. For example, in thick plate welding, it is necessary to select flux with a coarser particle size and moderate alkalinity to ensure good penetration and weld seam formation.
The use of submerged arc welding flux requires strict process management. The pressure vessel industry generally adopts a flux drying system to control the moisture content below 0.1%, in order to avoid hydrogen-induced cracking. At the same time, when recycling and reusing flux, it is necessary to screen out impurities and ensure the uniformity of particles, which is crucial for ensuring welding stability. With the popularization of automated welding technology, the compatibility of submerged arc welding flux with intelligent equipment has also become a research focus. For example, optimizing flux conveying efficiency through an online particle size monitoring system.
Welding of longitudinal and circumferential seams of cylindrical shells is a critical part of pressure vessel manufacturing, and the application of automated welding technology has greatly improved welding efficiency and quality.
Automated welding of longitudinal and circumferential seams of cylindrical shells is the core application of submerged arc welding in pressure vessel manufacturing. To achieve high-quality automated welding, it is necessary to precisely control various parameters during the welding process.
Welding Speed: The adjustment of welding speed should be based on the material, thickness of the cylindrical shell, and welding process requirements. Too fast a welding speed may lead to insufficient penetration and lack of fusion in the weld seam. Conversely, too slow a welding speed will cause excessive heat input, resulting in coarse grain structure in the weld seam and reduced mechanical properties. Therefore, in actual operation, it is necessary to find the appropriate range of welding speed through experiments and experience.
Current and Voltage: Suitable current and voltage can ensure good formation and fusion of the weld seam. In actual operation, it is necessary to find the best combination of current and voltage parameters according to the material, thickness of the welded piece, and welding process requirements, through experiments and experience. For example, for thick plate welding, it is necessary to appropriately increase the current and voltage to ensure the penetration and width of the weld seam.
Rotational Speed and Travel Speed: The rotational speed of the cylindrical shell and the travel speed of the welding carriage must be coordinated to ensure uniform and continuous weld seams. If the rotational speed and travel speed are not matched, it will lead to uneven and intermittent weld seams, affecting welding quality. Therefore, during the welding process, it is necessary to precisely control the rotational speed of the cylindrical shell and the travel speed of the welding carriage to keep them synchronized.
For the welding of longitudinal and circumferential seams of large pressure vessels, multi-head welding can also be used to further improve welding efficiency. Multi-head welding requires precise synchronization to ensure that the welding parameters of each head are consistent and the welding speed is coordinated. Through multi-head welding, the longitudinal and circumferential seams of large pressure vessels can be completed in a short time, greatly reducing the construction period and improving production efficiency.
In the welding process of pressure vessels, the recovery management of flux is an important link in reducing costs and improving welding quality. Rational recovery and reuse of flux can not only reduce waste but also lower production costs and reduce environmental pollution.
During the welding process of pressure vessels, some flux will be lost with welding spatter and slag. Therefore, the recovery management of flux is an important link in reducing costs and improving welding quality. Rational flux recovery management can not only reduce waste and lower production costs but also reduce environmental pollution.
The recovered flux needs to be screened, cleaned, and dried to remove impurities and moisture, ensuring that its performance meets welding requirements. Screening can remove large particle impurities and slag from the flux, cleaning can remove oil and dust from the surface of the flux, and drying can remove moisture from the flux to prevent defects such as porosity during the welding process. Through these processing methods, the performance of the recovered flux can be ensured to be stable and meet the requirements of the welding process.
The application of submerged arc welding in pressure vessel manufacturing involves multiple technical and management aspects. By improving skills, selecting and recovering flux reasonably, and regulating parameters in a standardized manner, the welding quality and production efficiency of pressure vessels can be significantly improved. In actual production, it is necessary to continuously optimize welding technology in combination with specific welding process requirements and equipment conditions to ensure the safe operation and efficient production of pressure vessels. With the continuous development of automated welding technology, the application prospects of submerged arc welding in pressure vessel manufacturing will be even broader.
