Is submerged arc welding (SAW) the most practical steel pipe welding technology

Submerged arc welding is suitable for heavy industrial applications such as steel pipe, pressure vessels and tanks, locomotive manufacturing, and heavy construction/excavation. It is highly suitable for industries requiring high productivity, especially those involving welding very thick materials, from which numerous benefits can be derived. Its high deposition rate and travel speed can significantly impact worker productivity, efficiency, and production costs, which is one of the key advantages of SAW. Other benefits include: excellent chemical composition and mechanical properties of SAW welds, minimal arc visibility and lower welding fumes, improved working environment comfort, and good weld shape and toe line.

Submerged arc welding uses a wire feeding mechanism that separates the arc from the air using granular flux. As the name suggests, the arc is buried in the flux, meaning that once the parameters are set, the arc is invisible as the next layer of flux flows out. The welding wire is continuously fed by a welding torch that moves along the weld seam. An electric arc heats and melts a section of welding wire, some flux, and base metal, forming a molten pool. After solidification, a weld covered with a layer of slag is formed. The thickness range of the welding material is 1/16”-3/4”, which can achieve 100% penetration welding through a single pass. If the wall thickness is not limited, multiple passes can be welded, and appropriate pretreatment of the weld and selection of suitable welding wire and flux combinations are necessary.

Selection of Flux and Welding Wire for Submerged Arc Welded Steel Pipes

(1) Selecting suitable submerged arc welding flux and welding wire for a specific submerged arc welding process is crucial for achieving optimal results using this process. Although submerged arc welding alone is efficient, productivity and efficiency can be improved based on the submerged arc welding wire and flux used.

(2) Submerged arc welding flux not only protects the weld pool but also contributes to improving the mechanical properties and productivity of the weld. The formulation of submerged arc welding flux has a significant impact on these factors, affecting current-carrying capacity and slag release. Current-carrying capacity refers to the ability to achieve the highest possible deposition efficiency and high-quality weld profile.

(3) Slag release from specific submerged arc welding (SAW) fluxes affects SAW flux selection, as some SAW fluxes are better suited for certain welding designs than others.

(4) Flux selection options for SAW include active and neutral types of welding. A fundamental difference is that active fluxes alter the chemical properties of the weld, while neutral fluxes do not.

Active fluxes are characterized by the presence of silicon and manganese. These elements help maintain weld tensile strength at higher heat inputs, help keep the weld smooth at higher travel speeds, and provide good slag release.

In general, active fluxes can help reduce the risk of poor weld quality and costly post-weld cleaning and rework. However, it's important to remember that active fluxes are generally best suited for single-pass or double-pass welding. Neutral fluxes are better for large, multi-pass welding because they help avoid the formation of brittle, crack-sensitive welds.