Double-Sided Submerged Arc Welding vs. Manual Welding for Straight Seam Steel Pipes

Submerged arc welding (SAW) is a highly efficient welding method invented in the 1940s. Like manual arc welding, it uses the principle of "slag protection," but instead of the electrode coating, the protective material is specially molten granular flux. The flux is continuously delivered to the welding area through a funnel and pipe, covering the arc.

Unlike manual welding, submerged arc welding uses welding wire as the electrode. The welding wire can be continuously fed, avoiding the interruption of welding due to frequent electrode head changes in manual welding, thus significantly improving welding efficiency. During welding, the continuously fed welding wire ignites the arc under the coverage of the granular flux. The flux partially melts and evaporates, forming a sealed cavity, within which the arc burns stably, hence the name "submerged arc welding."

Three major advantages of submerged arc welding:

1. Fully automated: Submerged arc welding automates the welding process. The welding wire is continuously fed, and the welding process requires no human intervention, significantly improving production efficiency and welding consistency.
2. High weld quality: The arc burns under the flux layer, resulting in excellent heat exchange and protection performance. This leads to high weld metal purity, fewer porosity and inclusions, and stable and reliable weld joint quality.
3. High current and high efficiency: Because the arc is covered by flux, the heat is concentrated, allowing for high-current welding (up to 1000A or more). This results in deep penetration and fast welding speed, making it particularly suitable for welding thick plates and large-diameter steel pipes.

Typical application: West-East Gas Pipeline Project

China's West-East Gas Pipeline project extensively uses high-strength pipeline steel (such as X70 and X80). Pipelines are prefabricated in 12-meter-long sections in the factory, and longitudinal seams are welded using double-sided submerged arc welding (internal welding first, then external welding), before being transported to the site for circumferential welding and assembly. Currently, submerged arc welding has evolved into twin-wire and multi-wire submerged arc welding. Multi-wire technology allows the simultaneous use of 2-5 welding wires, further improving deposition efficiency and welding speed.

Double-sided submerged arc welded straight seam steel pipes are increasingly widely used in building structures, oil and gas transportation, and pressure vessels. Compared to manual welding of large-diameter straight seam steel pipes, automatic submerged arc welding has significant advantages in efficiency, quality, and consistency.

Other efficient welding methods:

Gas shielded welding (GMAW/TIG): 

Gas shielded welding uses gas (not flux) as the protective medium. A protective gas (usually argon or an argon-rich mixture) is delivered to the arc area through the welding nozzle, displacing air and preventing weld oxidation. Its advantages include visible welding process, flexible operation, and a small heat-affected zone. It is widely used for welding stainless steel, aluminum, and thin plates. To improve welding efficiency and weld formation, 3%-5% carbon dioxide is sometimes added to the argon gas as an active gas.

Laser welding: 

Laser welding is a welding method that uses a high-energy laser beam as a heat source. Its characteristics include:

● It can penetrate transparent media, enabling welding inside sealed containers.
● It does not require vacuum protection and can be performed in the atmosphere.
● Heat input is precisely controllable, with an extremely small heat-affected zone.

● It has been widely used in the automotive, aerospace, and electronics industries, and has been successfully applied in the medical field (such as retinal repair surgery).

Read more: Basic Principle of High Frequency Welding (HFW)