process guide
Submerged Arc Welding (SAW): Complete Process Guide
How SAW works, where it's used, the equipment it needs, and how to fix the most common problems; from porosity to arc instability.
Submerged arc welding hides its arc beneath a layer of granular flux, giving it the highest deposition rates and deepest penetration of any common arc process, with barely any fume, spatter or arc flash. This guide covers how SAW actually works, where it's used, what equipment you need to run it, and how to diagnose and fix the problems that come up most often, from porosity to cracking.
If you're ready to buy, browse our sub arc welders for sale, otherwise, read on for how the process works.
What Is Submerged Arc Welding?
Submerged arc welding (SAW) is an arc welding process in which the welding arc is hidden beneath a continuously fed layer of granular flux. Unlike MIG or TIG welding, there is no visible arc during the process; the flux completely covers the weld pool. Protecting it from atmospheric contamination and suppressing the spatter, fumes, and UV radiation associated with open-arc processes.
The bare wire electrode feeds continuously into the joint, forming the weld as electrical current passes through it to the workpiece. As welding progresses, the flux immediately surrounding the arc melts and fuses, forming a protective slag layer over the weld bead. Unfused flux is recovered and recycled.
SAW is valued for its extremely high deposition rates, deep penetration, and consistent weld quality on heavy plate. Making it a go-to process in heavy fabrication, pressure vessel manufacture, shipbuilding, and structural steelwork.
Why Is Submerged Arc Welding Called “Submerged”?
Submerged arc welding gets its name from the flux layer that completely covers, or “submerges”, the arc and weld zone during the process. A flux hopper feeds granular flux ahead of and over the weld pool as the welding head travels along the joint. Because the arc is hidden beneath this layer, there is no visible arc flash during welding, which is one of the process’s distinctive safety advantages.
How Does the Submerged Arc Welding Process Work?
The SAW process uses an electrical current to create an arc between a continuously fed bare wire electrode and the base material.
The key steps are:
Because the weld pool is not visible during the process, correct parameter settings (current, arc voltage, and travel speed) are critical. These directly affect bead quality, chemical composition, and penetration depth.
Single Wire and Multi-Wire Operation
SAW is most commonly run as a single-wire process, but deposition rates and travel speeds can be significantly increased using multi-wire setups. Twin wire feed, tandem wire systems, and the addition of metal powder are all established methods for boosting productivity on high-volume applications. Tubular wire is another option in which alloy additions are required via the consumable.
What Are the Applications of Submerged Arc Welding?
Submerged arc welding is most suited to long, straight weld seams and circumferential welds on large rotating components.
Common applications include:
- Pressure vessels and storage tanks. The process produces strong, clean welds with deep penetration on carbon and stainless steels
- Structural steelwork. Longitudinal butt and fillet welds on heavy plate sections
- Shipbuilding and offshore structures. High deposition rates make it economical for long runs
- Pipe fabrication. Circumferential welds using a fixed weld head with the workpiece rotating on a positioner or pipe rotator
- Weld overlay and hard facing. Surfacing applications on components subject to wear
- Wind tower and pressure pipe manufacture. Spiral and longitudinal seam welding of large-diameter sections
Materials: SAW handles low-and medium-carbon steels, high-strength low-alloy steels, stainless steels, and some nickel-based alloys effectively.
What Equipment Is Needed for Submerged Arc Welding?
SAW requires more infrastructure than manual arc processes.
The core components are:
- Power source. A high-duty-cycle power source capable of the high output amperages the process demands; typically 800–1,200 amps for production applications. AC or DC current can be used depending on the application.
- Wire feed system and weld head. The weld head carries the electrode and flux delivery nozzle along the joint. In automated setups, this is controlled by a carriage, tractor, or column and boom manipulator.
- Control unit. Mechanised and automated SAW setups use a control unit to regulate wire feed speed, voltage, and travel speed, all of which directly affect weld quality.
- Flux hopper and recovery system. A hopper feeds granular flux onto the joint ahead of the arc. Most production setups include a flux recovery system to collect, sieve, and recirculate unused flux.
- Handling equipment. Because SAW is generally limited to flat and horizontal positions, the workpiece usually needs to be rotated or repositioned. Welding positioners, pipe rotators, and column and boom manipulators are all used alongside SAW systems to handle large weldments and maintain the correct welding position throughout.
What Is the Function of Flux in Submerged Arc Welding?
Flux in SAW serves several critical functions simultaneously:
- Shielding. The flux layer prevents atmospheric contamination of the weld pool, replacing the need for shielding gas.
- Heat concentration. Flux concentrates heat into the weld pool, enabling the deep penetration SAW is known for.
- Arc stability. Flux assists with arc striking and maintains arc stability throughout the weld run.
- Bead shaping. The molten flux controls the shape of the weld bead and surface finish.
- Alloying. Depending on the type, flux can contribute alloying elements to the weld metal to meet specific mechanical property requirements.
Correct flux selection, storage, and handling are essential. Damp or contaminated flux is one of the most common causes of porosity and quality issues in SAW.
Advantages of Submerged Arc Welding
- Very high deposition rates. Significantly higher than manual arc processes, making SAW highly productive on long runs
- Deep penetration. Capable of achieving full penetration on heavy plate with fewer passes than other processes
- Consistent weld quality. Mechanised operation removes variability from the human operator
- Minimal fume, spatter, and UV radiation. The flux cover makes SAW one of the cleaner arc processes to work around
- Low skill requirement. Once parameters are set, the process runs automatically
- No restriction on material thickness. Multiple passes with correct joint preparation allow virtually unlimited plate thickness to be welded
- Suitable for indoor and outdoor use. The flux shield is not disrupted by draughts, as shielding gas can be
Disadvantages of Submerged Arc Welding
- Limited to flat and horizontal positions. The fluid weld pool and molten flux mean SAW cannot be run in vertical or overhead positions
- High setup requirement. The process is not portable and requires significant fixturing and handling equipment
- Restricted material range. Most effective on carbon steels, low-alloy steels, and stainless steels; not suitable for all materials
- Post-weld cleaning. Slag removal and flux recovery add steps to the process, though flux recovery can be automated
- Parameter sensitivity. Because the weld pool is not visible, errors in current, voltage, or travel speed are not immediately obvious and can result in costly rework
Common Submerged Arc Welding Problems and How to Fix Them
Because the weld pool is hidden, SAW quality problems are often only discovered during post-weld inspection. Catching issues early (and knowing their root cause) saves significant rework cost.
Quick Reference: SAW Troubleshooting
| Problem | Typical Symptoms | Likely Cause | Fix |
|
Porosity
|
Voids or holes in the weld bead | Contamination; damp flux; travel speed too fast | Clean base material; dry or replace flux; adjust speed |
|
Lack of fusion
|
Weld metal not bonding with base plate | Low heat input; poor joint prep; incorrect electrode angle | Increase amperage/voltage; re-cut joint; realign electrode |
|
Cracking
|
Cracks in weld or HAZ after cooling | High residual stress; wrong preheat; hydrogen contamination | Apply correct preheat; use low-hydrogen consumables; consider PWHT |
|
Arc instability
|
Wandering arc; uneven bead; spatter | Incorrect stick-out; inconsistent flux coverage; wire feed issues | Set stick-out to 25–50 mm; maintain 25–50 mm flux depth; check wire feed |
|
Flux issues
|
Inconsistent bead; slag inclusions | Mixed or contaminated flux; damp storage | Follow manufacturer guidelines; sieve recovered flux; store sealed and dry |
Porosity
Porosity appears as small voids or holes within or on the surface of the weld bead. It is almost always caused by gas being trapped before it can escape the solidifying weld pool.
Causes: Oil, rust, or paint on the base metal; damp or improperly stored flux; travel speed too fast for gases to escape; flux coverage too shallow.
Fix: Ensure base material is clean and dry before welding. Store flux in sealed containers in a dry environment, and if moisture is suspected, rebake per the manufacturer’s guidance. Reduce travel speed slightly or adjust amperage to allow the pool to remain fluid long enough for gases to escape.
Lack of Fusion
Lack of fusion occurs when the weld metal fails to fully bond with the base plate or the previous weld pass. It can appear sound externally, but will fail under inspection or testing.
Causes: Insufficient heat input (amperage or voltage too low); tight root gap or incorrect bevel angle; electrode not directed at the joint sidewall.
Fix: Increase heat input. Re-cut or re-grind the joint to the correct geometry. Reposition the electrode so the arc strikes both the base material and the filler wire correctly.
Cracking
Cracks in or adjacent to the weld after cooling can be surface-visible or subsurface. Hydrogen-induced cracking is a particular risk on higher-strength steels.
Causes: High residual stress from rapid cooling; insufficient preheat or interpass temperature control on thick sections; moisture-contaminated flux or consumables introducing hydrogen.
Fix: Apply the correct preheat temperature for the material and thickness being welded. Use low-hydrogen consumables and maintain proper flux storage conditions. On critical components, post-weld heat treatment (PWHT) may be required to reduce residual stress.
Arc Instability
Arc instability produces an uneven, wandering arc that results in inconsistent bead width, surface finish, and spatter.
Causes: Electrode stick-out too long (increases electrical resistance) or too short (destabilises the arc); uneven flux coverage over the arc; worn contact tips or inconsistent wire feed.
Fix: Adjust stick-out to within the recommended range, typically 25–50 mm. Ensure consistent flux depth of 25–50 mm above the arc throughout the run. Inspect and replace worn contact tips, drive rolls, or other wire feed components.
Flux Handling and Storage Problems
Poor flux management results in inconsistent bead appearance, porosity, and slag inclusions.
Causes: Mixing recovered flux with virgin flux at the wrong ratio; flux contaminated by dirt, oil, or scale; flux stored in humid conditions.
Fix: Follow the manufacturer’s guidance on the permitted percentage of recovered flux. Always sieve recovered flux to remove fines and contaminants before recirculation. Store flux in sealed, humidity-controlled containers.
Preventative Maintenance Checklist
Regular attention to the following reduces unplanned downtime and keeps weld quality consistent:
- Check and replace contact tips and drive rolls at regular intervals
- Inspect the wire feed system for inconsistent feed or slippage
- Verify the flux hopper delivery rate is consistent
- Inspect flux recovery system filters and sieve condition
- Calibrate power source output against set parameters
- Check electrode stick-out before each production run
- Inspect joint preparation and fit-up before welding; gap, bevel angle, and surface condition
- Confirm flux is within shelf life and has been stored correctly
Frequently Asked Questions
What is submerged arc welding used for?
SAW is primarily used for long, straight weld seams and circumferential welds on large rotating components. Pressure vessels, storage tanks, structural steelwork, pipes, and wind tower sections are the most common applications. It is particularly effective on heavy plates where high deposition rates and deep penetration are needed.
Why is submerged arc welding referred to as submerged?
The arc is covered (submerged) beneath a layer of granular flux throughout the welding process. This flux layer shields the weld pool, concentrates heat, and suppresses fumes and spatter. Meaning there is no visible arc light during welding.
What are the main advantages of SAW over other welding processes?
The combination of very high deposition rates, deep penetration, consistent automated quality, and minimal fume and spatter makes SAW more productive and cleaner than most manual arc processes on the applications it suits. The trade-off is that it is limited to flat and horizontal positions and requires significant handling equipment.
What causes porosity in submerged arc welding?
The most common causes are contamination of the base material (oil, rust, or paint), damp or poorly stored flux, and travel speed too fast for gases to escape before the pool solidifies. Checking material prep and flux condition before welding prevents most porosity issues.
Can submerged arc welding be done manually?
Yes, though it is less common. Manual SAW uses a pressurised or gravity-fed flux delivery system and a hand-held torch. However, the process is most productive when mechanised or fully automated; the inability to see the weld pool makes manual operation challenging and parameter setting more critical.
What equipment does Westermans stock for submerged arc welding?
Westermans holds used and refurbished submerged arc welders from manufacturers including ESAB, Lincoln Electric, and Miller. Alongside column and boom manipulators, pipe rotators, and welding positioners used to handle workpieces during the SAW process. View current SAW equipment availability or contact us to discuss your requirements.
SAW Equipment From Westermans
Westermans has supplied refurbished submerged arc welding systems to fabricators worldwide for over 50 years. Our stock includes complete SAW setups and individual components, like power sources, weld heads, column and boom manipulators, pipe rotators, and welding positioners.
“The ESAB submerged arc welding system attached to the Bode column and boom manipulator has allowed us to carry out high deposition rate welding during the latter part of jetty construction sections, increasing our skill levels in the process whilst rapidly recouping its initial cost.”
— Responsive Engineering UK
View submerged arc welding equipment for sale | Sell your SAW equipment to us
