What is submerged arc welding (SAW)? An easy guide

Submerged arc welding, often called subarc welding, is the go-to process for fabricating ships, bridges, and pressure vessels. It can produce deep, smooth seams while keeping the arc completely hidden under a blanket of granular flux. 

What is submerged arc welding?

Submerged arc welding (SAW) is an automatic or semi-automatic welding process that joins metals by creating an electric arc between a continuously fed consumable electrode and the workpiece. It is unique because the entire arc and molten zone are completely covered or “submerged” under a layer of granular flux. 

This flux melts partially during welding, protecting the molten metal from air contamination and forming a layer of slag that solidifies over the weld bead.

The term “subarc welding” is simply a shortened name for the same process. It was first developed in the 1930s and quickly became a cornerstone of industrial fabrication because of its unmatched efficiency for thick steel sections. 

Over time, engineers refined the process with automatic wire feeding and flux recovery systems, making it even faster and more consistent.

Its reliability has kept it relevant for nearly a century. The global submerged arc welding market is expected to reach $11.9 billion by 2030. Even in an age of laser and robotic welding, SAW continues to dominate where heavy steel meets precision.

Today, SAW remains one of the most dependable methods for producing high-quality welds in heavy manufacturing. It is primarily used when automation or robotic systems handle long, continuous joints with minimal supervision.

How submerged arc welding works

Submerged arc welding works by generating an electric arc between a continuously fed electrode wire and the base metal, all hidden beneath a thick layer of granular flux.

It typically follows four main stages:

1. Setup: The welder or automated system prepares the power source, electrode wire, and flux delivery unit. The electrode is usually a solid or tubular wire, while the flux is poured from a hopper to form a protective blanket over the joint.
2. Operation: As the arc strikes beneath the flux, it melts both the electrode and the base metal, creating a molten weld pool. Because the arc is submerged, it stays stable and free from atmospheric interference, allowing higher currents and faster welding speeds.
3. Weld formation: The molten metal mixes with flux to form a clean, uniform weld. The molten flux that interacts with the weld solidifies into a slag layer, which protects the cooling metal and prevents oxidation.
4. Finishing: Once the weld cools, the slag is chipped or brushed away, revealing a smooth bead. Unused flux is collected and recycled for the next pass, making the process both efficient and economical.

SAW is typically performed in flat or horizontal positions, which helps maintain uniform penetration and high deposition rates. It’s also highly compatible with automation and robotic systems, where consistent speed and torch angle can be maintained for long, continuous welds.

Key benefits of subarc welding

The key benefits of submerged arc welding include deep penetration, high weld quality, operator safety, and strong cost efficiency while being fully compatible with modern automation systems.

• Deep penetration and high deposition rates: SAW delivers exceptional depth of fusion, making it ideal for welding thick plates in a single pass. Its high deposition rate means faster production with fewer passes required.
• Excellent weld quality: Because the arc is completely covered by flux, the molten pool is shielded from air and impurities. The result is a clean, uniform weld with minimal spatter, low porosity, and consistent mechanical strength.
• Operator safety: The submerged arc reduces visible arc light, radiation, and excessive fumes. This not only makes the process safer but also reduces fatigue for operators working long shifts in fabrication shops.
• Cost efficiency in volume production: Continuous wire feeding and the ability to reuse flux make SAW quite economical for large projects. It reduces rework and consumable waste, offering a strong return on investment for industries that weld around the clock.
• Automation compatibility: SAW integrates easily with robotic systems and automated track welders. Companies using robotic welding machines can automate long, repetitive welds with precision while maintaining consistent quality and speed.

Common applications of submerged arc welding

The most common applications of submerged arc welding include shipbuilding, pipelines, structural steel, and wear-resistant overlays. These are the industries that depend on high-strength, repeatable welds for thick metal fabrication.

Shipbuilding and offshore structures

Major shipyards are implementing one-side submerged arc welding systems with automated panel lines for butt joint welding. Equipment manufacturers like Castellini have installed OSW (One Side Welding) technology at facilities, including Fincantieri Riva Trigoso shipyard, capable of welding plates up to 20 mm thick in butt weld configuration.

SAW can achieve deposition rates up to 45 kg/hour, significantly cutting fabrication time. Because of its predictable heat control and arc stability, it’s often automated for straight-line seams on large panels and offshore structures.

Standard Bots’ long-reach motion control and weld integration approaches support this same class of straight-line, high-repeatability seams and are useful for panel lines and offshore modules.

Pipelines, pressure vessels, and heavy equipment

SAW’s ability to produce smooth, uniform welds over long distances makes it ideal for pressure vessels, pipelines, and construction machinery. Miller Electric highlights that operations typically use SAW in demanding heavy industrial applications such as pressure vessel fabrication, shipbuilding, and offshore oil rig welding, where its deep penetration and high deposition rates excel at handling thick plate materials.

The process is also widely used for overlay welding, where corrosion- or wear-resistant alloys are applied to the inner surfaces of pipes and tanks. Weld overlay systems can extend equipment life in oil and gas, mining, and heavy industrial applications by providing corrosion and wear resistance.

Structural steel and large fabrication

SAW is a staple in bridge, building, and heavy machinery fabrication. It handles long seams in flat and horizontal positions without interruption, maintaining strength and precision across thick plates. 

Market data shows that the increased adoption of high-strength steels and the desire for more welding efficiency and productivity are also among the factors adding to growth in the market.

Overlays, wear-resistant surfaces, and specialty uses

Beyond standard joints, SAW excels in producing wear-resistant or corrosion-resistant coatings. The combination of flux and filler wire can be customized for carbon steel, stainless, or nickel-based alloys. Hobart Brothers documents several flux-wire combinations for cladding applications in offshore structures, pressure vessels, heavy equipment, and wind towers, ensuring longer equipment service life.

Research also shows that SAW has been successfully adapted for arctic-grade steel structures, where precise heat control and alloy selection are important for cold-weather performance.

Automation in SAW systems

SAW automation is common across large fabrication setups. Column-and-boom stations, gantries, tractors, and positioners handle straight or circular seams with steady precision. Multi-wire heads and strip cladding setups push deposition rates into the tens of kilograms per hour while keeping penetration uniform. 

Sensors like seam tracking, arc-voltage control, and flux recovery ensure consistent weld quality and minimal cleanup.

Standard Bots Core and Thor can integrate into these automated cells as manipulators or part handlers. Their motion control and I/O systems sync easily with SAW power sources and flux units, while no-code programming allows quick changeovers between weld types or component sizes.

Limitations and considerations

The limitations and considerations include post-weld slag removal, position restrictions, material quality, need for flux management, limited visibility, and equipment requirements.

• Post-weld slag removal: Although slag formation protects the weld during cooling, it must be removed manually or mechanically afterward, which adds an extra production step.
• Limited to flat or horizontal positions: SAW relies on gravity to hold the molten flux and weld pool in place, which makes it unsuitable for vertical or overhead welding. Attempts to use it in these positions often lead to poor bead shape and slag entrapment.
• Not ideal for thin materials: The process uses high current and produces significant heat, which can easily warp or burn through thin sheets below about 5 mm in thickness. SAW is generally reserved for thicker sections where deep penetration is required.
• Requires flux handling and recovery systems: Flux must be stored, delivered, and recycled carefully to maintain weld quality. Contaminated or damp flux can introduce porosity or inclusions. Industrial SAW lines often include vacuum-based flux recovery systems, adding to setup cost and maintenance.
• Limited visibility of the arc: Since the arc is fully submerged under flux, operators cannot see the weld pool directly. This makes manual adjustment or inspection during welding difficult without automated monitoring sensors or cameras.
• Space and equipment requirements: SAW setups are typically larger than those for TIG or MIG welding. The process needs a dedicated flux hopper, wire feed system, and recovery unit, which may not suit small workshops or confined spaces.
• Best ROI in high-volume production: Due to its equipment cost and preparation time, SAW delivers the best value in continuous or large-scale fabrication runs. For short or custom welds, setup time may outweigh its efficiency benefits.

Understanding these constraints helps manufacturers plan better setups and achieve a stronger return on investment.

Summing up

Submerged arc welding continues to prove its worth in modern heavy fabrication. Its ability to produce deep, uniform welds with minimal defects makes it a trusted process for industries where structural integrity matters most. 

The combination of flux shielding, high deposition rates, and automation compatibility allows manufacturers to weld faster and safer while maintaining consistent quality across large assemblies.

As factories shift toward smarter, more connected systems, SAW remains an essential part of automated welding cells. With the right setup, it delivers exceptional performance and a strong long-term return on investment.

Next steps with Standard Bots’ robotic solutions

Looking to upgrade your automation game? Standard Bots Thor is built for big jobs, while Core is the perfect six-axis cobot addition to any welding or fabrication setup, delivering unbeatable precision and flexibility.

• Affordable and adaptable: Core costs $37k. Thor lists at $49.5k. Get high-precision automation at half the cost of comparable robots.
• Perfected precision: With a repeatability of ±0.025 mm, both Core and Thor handle even the most delicate tasks.
• Real collaborative power: Core’s 18 kg payload conquers demanding welding and material-handling jobs, and Thor’s 30 kg payload crushes heavy-duty operations.
• No-code simplicity: Our intuitive, no-code app makes it easy to teach Standard Bots robots to do everyday tasks. So, Core and Thor integrate smoothly with industrial welding cells for advanced automation.
• AI-driven models: For complex, high-variance, and unpredictable tasks that are otherwise impossible to automate today, Standard Bots robots learn through our AI-driven vision-to-action models, similar to how full self-driving works.
• Safety-first design: Machine vision and collision detection mean Core and Thor work safely alongside human operators.

Schedule your on-site demo with our engineers today and see how Standard Bots Core and Thor can bring AI-powered greatness to your shop floor.

FAQs

1. What is submerged arc welding?

Submerged arc welding is a process where an electric arc burns beneath a layer of granular flux. The arc melts both the electrode and base metal, creating a clean, high-strength weld protected from air contamination.

2. How does subarc welding differ from MIG or TIG welding?

Subarc welding differs from MIG or TIG welding because the arc and molten pool are completely covered by flux. This shielding eliminates visible light, fumes, and spatter, allowing higher currents and deeper penetration, which is ideal for thick materials.

3. What are the main benefits of submerged arc welding?

The main benefits of submerged arc welding include deep weld penetration, fast deposition rates, minimal spatter, and superior weld quality. It’s also safer for operators since the arc is hidden, reducing UV and fume exposure.

4. Which industries rely most on subarc welding?

Industries that rely most on subarc welding include shipbuilding, pipeline construction, pressure vessel fabrication, and heavy equipment manufacturing. These sectors use SAW for its strength, consistency, and ability to handle large, continuous joints.

5. What are the limitations of SAW?

The limitations of SAW are that it’s restricted to flat or horizontal positions, unsuitable for thin materials, and requires flux handling systems. It also demands more space and is best suited for large-scale, repetitive production.

6. Can submerged arc welding be automated?

Yes, submerged arc welding can be automated. Robotic and mechanized SAW systems are common in modern factories, integrating wire feeding, torch travel, and flux recovery for consistent, high-speed welding performance.