Sub Arc Welding: The Complete Guide to SAW Process

A fabrication shop was quoted three days to seam-weld a stack of 2-inch bridge girders with stick electrodes, until a supervisor swapped in a submerged arc rig and finished the same joints before lunch. That hidden, flux-buried arc is why sub arc welding still runs the heaviest seams in steel construction.

What Is Sub Arc Welding and Why Does It Matter?

A fabrication shop once quoted three full days to seam-weld a stack of 2-inch bridge girders with stick electrodes. The supervisor rolled a submerged arc rig into position, buried the arc under granular flux, and the joints were finished before lunch. That hidden arc is why sub arc welding still handles the heaviest seams in steel: bridge girders, ship hulls, pressure vessels, and wind tower shells.

Wondering what “sub arc” means? It is an automatic welding process where the arc is completely covered, or “submerged,” by a layer of fusible granular flux. The arc never sees daylight, and that single choice changes how the whole process behaves.

A Plain-Language Definition

Sub arc welding is formally known as submerged arc welding, abbreviated SAW. The SAW process is defined by the AWS Welding Handbook as coalescence produced by an arc between one or more bare metal electrodes and the workpiece, shielded by a blanket of granular, fusible material called submerged arc welding flux.

Three words in that definition do the heavy lifting:

• Bare metal electrode — unlike a stick electrode, sub arc wire has no flux coating. All shielding comes from the granules around it.
• Granular, fusible flux — the flux melts as the arc burns through it, forming liquid slag that protects the molten puddle.
• Arc or arcs — most setups run one wire, but tandem and multiwire systems with up to four wires are routine in heavy plate work.

In practice, a machine feeds continuous bare wire into a pile of flux, strikes an arc underneath, and travels along the joint. The operator never sees it; what emerges is a finished bead covered by hard solidified slag, chipped off when cool.

Where Sub Arc Welding Came From

The process is older than most expect: the first SAW patent was filed in 1935, when shipyards and rail car builders wanted long plate seams welded faster than a hand-held stick allowed. Early systems were bulky, but the core idea — bury the arc in flux — has survived nine decades, with modern rigs adding digital controls and smarter flux formulations (history and development of the process).

According to EPA AP-42 Chapter 12.19, SAW accounted for roughly 4 percent of welding electrodes consumed in the United States back in 1991. That sounds small until you remember the market is dominated by millions of small stick and MIG jobs. By weight of weld metal, one sub arc station can deposit more in an hour than a dozen stick welders do in a shift.

Why Heavy Fabrication Keeps Choosing It

Sub arc dominates thick-steel work because you trade position flexibility for raw productivity and weld quality:

• Very high deposition rates. A single-wire setup approaches 40 pounds of weld metal per hour; multiwire systems pass 100 pounds.
• Deep, consistent penetration. Concentrated heat lets sub arc weld thick sections in fewer passes than most processes.
• Excellent bead appearance. A stable, shielded arc lays down smooth, uniform welds that are usually spatter-free.
• Low operator fatigue. The machine handles travel and feeding; the operator monitors parameters rather than manipulating a torch.
• Reduced arc hazard. The flux blanket suppresses spatter, arc light, fumes, and ultraviolet radiation compared with shielded metal arc welding.

That containment is why sub arc stations can sit beside grinding and fitting work without shutting down the bay.

Where You Will See the SAW Process in the Real World

• Longitudinal and circumferential seams on pressure vessels and storage tanks
• Web-to-flange welds on plate girders for bridges and buildings
• Pipeline girth welds in specialized mechanized configurations
• Ship hull plate seams and bulkhead fabrication
• Wind tower shell longitudinal seams
• Hardfacing and buildup overlays on worn components

The common thread is thick carbon or low-alloy steel, a flat or rolling joint, and enough weld metal that the economics swing hard in sub arc’s favor. Filler choice follows base metal chemistry, as our alloy steel welding electrodes guide explains.

Sub arc has limits: it is basically a flat and horizontal position process, it struggles on thin sheet, and it fits poorly with short, interrupted welds or awkward field repairs. That is why stick welding still wins in maintenance and out-of-position work, and why most shops run it alongside other processes.

The One-Sentence Answer

So what is sub arc welding? It is submerged arc welding, an automatic process in which a bare wire electrode and the workpiece are joined by an arc buried under granular fusible flux, producing deep-penetrating, high-deposition welds with minimal spatter, fume, and arc radiation. What follows covers how that buried arc behaves.

How the SAW Process Works: Step by Step

While the arc may be out of sight, the submerged arc welding (SAW process) is a carefully timed sequence of physics. Rather than relying on a blanket of shielding gas, this method buries its arc beneath granulated flux to create the clean, high-deposition welds seen in heavy steel fabrication. Here is how that hidden arc goes from insulation to a finished bead.

1. Flux Deposition

Every SAW weld begins before striking the arc. The flux hopper lays down a generous, consistent layer of dry, granulated flux directly over the joint. At room temperature, this cold flux is an electrical insulator. By blanketing the seam in advance, it prevents any contact between the open air and the molten metal to come. The width and depth of this layer are not guessed, they are set to fully bury the arc for the chosen parameters.

2. Arc Initiation Under the Flux

With the joint covered, the continuously fed electrode is brought into contact with the base metal. Because the flux above it is non-conductive, a direct short is often used to strike the arc. Other methods, such as a small piece of steel wool or high-frequency starting, can be used depending on the equipment. The moment this arc is established, intense heat begins to rapidly melt both the tip of the electrode and the surrounding flux. This is the key transition: once molten, the flux loses its insulating properties and becomes conductive, allowing the arc to sustain itself beneath the blanket.

3. Molten Pool Formation and Metal Transfer

Now buried from view, the arc reaches temperatures capable of fusing the base metal and the filler metal together. The filler metal comes from the continuously fed electrode and, on some setups, supplemental welding wire or metal granules. As droplets transfer across the arc, they join the growing weld pool. Simultaneously, the melted flux reacts with impurities, helping to refine the weld metal. At the same time, the unmelted portion of the flux around the pool continues to act as a thermal insulator, keeping the heat concentrated exactly where it needs to go.

For heavier joints utilizing alloy steel welding electrodes, this concentrated heat is especially beneficial, as it can achieve deep penetration without needing to excessively widen the joint preparation.

4. Slag Formation and Bead Shaping

As the arc travels forward, the molten flux floats to the surface of the weld pool. Here, it solidifies into a layer of protective slag. This slag does two crucial jobs. First, it shields the still-hot weld metal from oxygen and nitrogen as it cools. Second, it slows the cooling rate, which helps to form a smoother, more uniform bead contour. Unlike a bare arc, the shape of an SAW bead is largely influenced by this fluid slag, not just the surface tension alone. Once cooled enough, the brittle slag is chipped off to reveal the finished weld.

5. Flux Recovery and Reuse

Not all of the granulated flux is consumed. As noted in AWS technical guidance for submerged arc welding, between 50 and 90 percent of the flux is recoverable. A vacuum flux recovery system collects the unused, un-melted granules from around the weld, screens out any slag chunks or spatter, and feeds them back to the hopper for reuse. With proper handling and storage, this recycling drastically cuts consumable waste for large, production-scale runs.

6. The Self-Adjusting Arc Principle

The final piece of this process is its built in stability. With a constant voltage power source, SAW operates on what is known as the self-adjusting arc principle. If the arc length tries to shorten from changes in fit-up, the current increases, melting more electrode to compensate. If the arc length grows, the current drops and slows melting. This automatic correction keeps the arc length consistent without the need for minute manual adjustments, a major reason why SAW is so well suited for mechanized and automatic welding.

SAW Equipment and System Setup

Submerged arc welding earns its reputation for high deposition rates, but the arc is only half the story. The other half is the rig around it: a power source, a wire drive, a flux delivery system, and something that moves the whole package along the joint at a steady speed. Set those pieces up correctly and SAW runs almost by itself. Set them up poorly and you get erratic arcs, cold lap, and a pile of expensive rework.

This section walks through the full system, component by component, so you know what each part does and what to check before striking an arc. The AWS Welding Handbook chapter on submerged arc welding is a useful reference for standard equipment configurations if you want to go deeper.

The Power Source

SAW draws heavy current for long stretches, so the power source is built for endurance rather than portability. Most industrial units operate at a 100 percent duty cycle, meaning they can run continuously at rated output without overheating. That matters on a 20-foot girders seam that never stops.

Current demand scales with plate thickness: roughly 350 A on thinner material up to and beyond 1,000 A on heavy plate, especially with tandem or multiwire setups. Because SAW uses a constantly feeding bare wire rather than a coated stick electrode, the arc has a stable voltage that is easy to regulate, which is why constant-current (CC) and constant-voltage (CV) machines both appear in service.

• DC gives the deepest, most stable penetration and is the most common choice.
• AC reduces arc blow on heavy, out-of-position-adjacent work and is often used in tandem-wire systems to limit interference between arcs.
• CV pairs naturally with a constant-speed wire feed for short-arc-free, high-current production welding.

Wire Feed, Drive Rolls and the Welding Head

The wire feeder is the heartbeat of the system. It pulls electrode wire from a coil or drum, straightens it, and pushes it through the conduit to the contact tip at a precise, repeatable rate. Drive rolls must match the wire diameter; the wrong groove size causes slippage, surging, and inconsistent stick-out.

Wire sizes for automatic SAW commonly run 1/8, 5/32 and 3/16 in. Semiautomatic guns, which an operator hand-handles, use lighter wire from 1/16 to 3/32 in. to keep the gun manageable. A wire straightener removes the memory curve from coiled wire so the electrode enters the contact tip dead straight, which directly affects where the arc lands in the joint. For a broader look at how wire types differ, our guide to all position welding rod selection covers the trade-offs in more detail.

The torch, or welding head, holds the contact tip, guides the wire into the flux pile, and carries the flux nozzle alongside it. On mechanized rigs it is rigidly mounted so travel angle and work offset stay fixed for the entire pass.

Flux Delivery and Recovery

A hopper mounted above the head gravity-feeds granulated flux through a nozzle, burying the arc completely before any light escapes. Directly behind the weld, a vacuum recovery unit sucks up unused, unfused flux for screening and reuse. Reclaiming flux is standard practice and saves real money, but only if it is screened to remove fines and slag contamination before it goes back in the hopper.

Carriage, Controls and Backing Strips

Because SAW is normally limited to flat and horizontal-fillet positions (1F, 1G and 2F), the work sits still and the machine moves. A track-mounted carriage, column-and-boom manipulator, or fixed gantry carries the head along the seam at a controlled travel speed. Controls regulate wire feed speed, arc voltage, travel speed and flux coverage, and modern units log all four for traceability.

On full-penetration butt joints, a steel or copper backing plate under the seam does two jobs: it supports the large molten weld pool so it does not blow through, and it helps control penetration depth. Copper pulls heat away faster and yields a shallower, cleaner root; steel backing is cheaper and can be left in place.

Three Operating Modes

Mode	Who moves the torch	Typical use
Semiautomatic	Operator by hand, machine feeds wire	Short runs, repairs, field work
Machine / mechanized	Fixed head, operator supervises	Repeatable shop seams, circumferentials
Automatic	Carriage or gantry, closed-loop controls	Long production seams, multi-shift girders and plate

Getting the rig dialed in is a shop discipline, and equipment selection is only part of it. If you are still building out your setup, the Airgas welding equipment guide is a practical starting point for matching machines to the work you actually do.

SAW Consumables: Electrodes and Flux Classification

Sub arc welding looks simple: feed wire into a pile of flux, strike an arc, move along the joint. But the weld metal inside a pressure vessel or bridge girder is only as good as the consumables chosen before the machine switches on. In SAW, consumables do far more than fill the joint. Flux shapes the arc, shields the pool, adds or removes alloying elements, and decides whether the finished weld passes its mechanical tests. Get the pairing right and the process practically runs itself; get it wrong and no amount of parameter tuning will save the joint.

The Standards Behind SAW Filler Metals

Two AWS specifications cover almost everything a SAW operator will touch. AWS A5.17/A5.17M governs carbon steel electrodes and fluxes, and its current edition was approved by ANSI on February 25, 2025, revising the 2019 edition. For low-alloy and stainless steel work, the governing document is AWS A5.23/A5.23M, which covers the same consumable families with chemistry and toughness requirements matched to those alloys. Understanding alloy steel welding electrodes and how they are selected pays off here, because the classification logic in A5.23 mirrors what many welders already know from stick electrode specs.

Both specifications follow the philosophy the rest of the AWS filler metal family uses: consumables are qualified through all-weld-metal test welds made with a classified electrode in a classified flux, and the resulting mechanical properties become part of the classification itself. The AWS Welding Handbook chapter on submerged arc welding describes this system in detail if you want the full technical treatment.

How to Read a Flux Classification

Unlike stick electrodes, where the designation tells you the deposited metal chemistry, an SAW flux classification tells you what that flux produces when paired with a classified wire. A typical designation looks like F7A6-EM12K:

• F identifies the consumable as a flux.
• 7 is the required tensile strength range (here 70 ksi minimum).
• A means all-weld-metal test requirements apply.
• 6 indicates the Charpy V-notch impact test temperature and energy requirement.
• EM12K is the classification of the wire the flux was qualified with.

That wire suffix matters more than most beginners realize. The flux is not classified as a standalone product; it is classified as a system. Substituting a different wire class without rechecking the combination can push weld metal chemistry, tensile strength, or toughness out of the range the procedure was qualified for.

Active Fluxes vs Neutral Fluxes

Fluxes fall into two broad behavioral categories, and the difference comes down to chemistry.

Active fluxes are formulated with ingredients that transfer silicon and manganese into the weld metal. They are economical and effective for single-pass welds on thinner material, where that extra alloying helps hit the required weld metal chemistry quickly. The catch is real: active fluxes are not recommended for multipass welding because manganese progressively builds up in successive passes and degrades toughness. In heavy multipass work, that buildup can quietly push impact values below spec.

Neutral fluxes produce weld metal chemistry that stays within tight limits regardless of the number of passes, current, or polarity. They are the default choice for thick-section multipass welding, where consistent toughness through the full joint depth is non-negotiable. The July 2025 Welding Digest practical guide to SAW walks through this choice in more depth for production teams.

Fluxes are also manufactured in two physical forms. Fused fluxes are melted, cooled, and crushed into granules; they resist moisture pickup and produce consistent, smooth beads. Agglomerated (bonded) fluxes are made by coating a core with a silicate binder and baking, which makes it easy to add alloying powders, though they pick up moisture faster than fused types.

Solid Wire, Metal-Cored Wire and Matching Pairs

Most SAW work runs on solid bare wire, commonly supplied in diameters from 3/32 in. to 5/32 in. (2.4 to 4.0 mm) on 14, 18, or 24 in. spools or coils. Metal-cored wire is the higher-output alternative: the tubular cross section carries more flux-equivalent alloying inside the wire itself, delivering higher deposition rates and better gap bridging on imperfect fit-up, at a higher cost per pound. Both are classified under the same A5.17 and A5.23 systems, and both must be matched to a flux qualified for that wire class. Reputable suppliers such as Airgas welding supplies can confirm compatibility, but the specification number on the consumable box is the final authority.

Flux Storage and Conditioning Rules

Moisture is the enemy of SAW consumables, and flux is porous enough to absorb humidity straight out of the air.

A few habits prevent most consumable-related defects. Store bags and drums off the floor on pallets, in a dry, climate-controlled area. Keep opened containers sealed between shifts. Screen reclaimed flux before reuse to remove fines and slag chips, and never reclaim flux that has been contaminated with oil, paint, or rust scale. The Canadian Metalworking SAW tech tips article is a useful shop-floor reference on screening and reclamation practice.

Treat the flux and wire pairing as a single, specified system rather than two independent purchases. When the consumable spec is locked in before the first pass, weld metal chemistry, mechanical properties, and inspection results stop being surprises and start being certainties.

Process Parameters and Welding Productivity

Every SAW machine has a handful of dials that decide whether a weld is clean, deep-penetrating and fast, or full of trouble. In submerged arc welding those settings matter more than in almost any other process: the arc is buried under flux, so no welder is watching the puddle to compensate. Set the machine right, or find out at inspection. Five variables do the heavy lifting.

The Five Variables That Control Your Weld

Treat them as a system, not a row of knobs; change one and the others react.

• Wire feed speed controls amperage, because SAW runs as a self-regulating constant-voltage process. More wire means higher current, which melts more metal, digs deeper and widens the fusion zone.
• Arc voltage sets arc length, and arc length sets bead shape. Higher voltage gives a flatter, wider bead and higher flux consumption; too little produces a narrow, ropey, high-crowned bead that traps slag.
• Travel speed sets deposition per inch. Fast travel thins the bead and cuts penetration; slow travel piles metal up and invites burn-through.
• Stick-out, or electrode extension (contact tip to work distance), changes resistance heating in the wire. Short stick-out runs cooler and stiffer; long stick-out preheats the wire and boosts melt-off, but excessive extension loses arc control.
• Polarity shifts where the heat lands. DCEP concentrates heat on the workpiece for deeper penetration; DCEN pushes more heat into the wire for higher melt-off and shallower penetration, with AC in the middle.

AWS covers these fundamentals in its Submerged Arc Welding reference, and the 2025 Welding Digest practical guide is the companion to reach for when you want real setup numbers.

How Each Variable Shapes the Bead

Trade press has documented these effects for decades; here is the summary that matters on the floor:

Change This	Effect on Penetration	Effect on Bead
Increase WFS / amperage	Deeper	Wider, more deposition
Increase arc voltage	Slightly less	Flatter and wider
Increase travel speed	Less	Narrower, thinner
Longer stick-out	Less	Higher melt-off, less stable
Switch DCEP to AC	Slightly less	Higher wire melt-off rate

Voltage and current interact, which is where beginners get burned: raising current to bury a joint deeper also raises arc force, so nudge voltage up. Change one variable at a time.

Polarity and the AC Advantage

Polarity is the most overlooked parameter, yet it changes productivity with a single switch. Welding on AC rather than DCEP melts wire more efficiently, because the arc spends half its time in each direction: in practice you can raise wire feed speed and deposition rate by roughly 15 to 25 percent at the same amperage compared with DCRP. That is why high-output tandem and multi-wire rigs mix AC and DC arcs, and AC also cuts arc blow, the magnetic deflection that plagues DC on long seams. If scrap is climbing on thick plate while you run straight DC, testing AC pays for itself. The Fabricator’s article on improving deposition rates with submerged arc welding breaks down the wiring schemes and current mixes.

Deposition Rates: Where SAW Pulls Ahead

Now the payoff. Deposition rate is the weight of filler metal melted and deposited per hour, and it is why SAW exists. A good stick welder running E7018 flat manages 5 to 6 lb/h; SAW has approached 100 lb/h (45 kg/h), against roughly a 10 lb/h (5 kg/h) theoretical maximum for SMAW.

• Single-wire SAW: up to about 40 lb/h in flat or horizontal work.
• Tandem systems: two torches feeding one puddle commonly reach 60 to 80 lb/h.
• Multi-wire and triple-arc setups: three or more torches regularly exceed 100 lb/h.

Lincoln Electric’s contrast of single-arc and triple-arc configurations shows the gap: often two to three times the output for the same floor space and the same operator attention. On thick plate it also cuts interpass cleaning, flux handling and rework. The Canadian Metalworking piece on SAW tech tips and fundamentals is a solid field reference.

Turning Numbers Into a Working Procedure

High deposition only helps if the weld is sound. Build the procedure from the joint outward: choose current for the penetration the design needs, set voltage for a bead shape that cleans up easily, then adjust travel speed to hit fill rate without overheating the plate. Keep a log of settings, plate thickness, joint prep and inspection results — with a hidden arc, your records are the only reliable feedback. SAW also cannot reach out-of-position joints, so shops pair it with manual processes; our guide to all-position welding rods covers the filler that handles those.

Dialed in, those numbers stop being abstract: a two-wire rig depositing 70 lb/h instead of 15 turns a multi-day seam into an afternoon, which is exactly why sub arc welding still runs the heaviest seams in steel construction.

Where Sub Arc Welding Is Used: Applications and Materials

Submerged arc welding (SAW) is almost exclusively a shop process. It thrives where heavy plate can be tacked, rolled, or held by a gantry to keep the torch perfectly still. As stated in AWS Welding Handbook coverage of the process, SAW became the default for heavy plate fabrication because of its ability to produce deep, clean, high-deposition welds at speeds that stick electrodes simply can’t match.

Industries That Rely on SAW

Pressure vessels and boilers. Longitudinal and circumferential seams on shells, heads, and nozzles are classic SAW work. Shops like Alamo Welding & Boiler Works use it to meet ASME requirements where consistency across thick-walled vessels is non-negotiable.

Structural plate girders and beams. Built-up plate members, flange-to-web fillet welds, and cap welds are all common SAW applications. Many of these fall under the qualifications of AWS D1.1, Structural Welding Code.

Pipelines and line pipe. SAW is widely used to weld longitudinal seams in API-grade line pipe. With tandem-wire or narrow-gap setups, it’s also used for certain shop girth joints where long, straight seams allow for maximum efficiency.

Shipbuilding. Hull plating, deck seams, bulkhead joints, and stiffeners are often welded by SAW bridges traveling along large panel lines. For marine work, procedures are guided by AWS D3.5, Guide for Welding Hull Structural Steel.

Tanks and cylindrical work. Storage tanks, silos, and pipe sections are often welded on turnrolls, allowing the circumferential seam to stay in the flat position. This is one of SAW’s most economical uses.

Power generation and surfacing. Heavy components like hydro turbine stay rings, runners, and segments can be joined or built up with SAW. For wear or corrosion protection, strip-electrode SAW is often used to apply stainless or nickel-bearing overlays to carbon steel without needing to replace the entire component.

Materials SAW Handles Well

SAW is predominantly an iron-based process. The materials it is most suited for include:

• Carbon steels: From mild plate up to heavy structural grades, making up the bulk of SAW work.
• Low-alloy steels: Used when toughness or elevated-temperature strength is required, matched with filler metals per AWS A5.23/A5.23M. For a breakdown of these classifications, see our guide to alloy steel welding electrodes.
• Stainless steels: Welded as solid stainless plate or cladded over carbon steel.
• Nickel-based alloys: Primarily used for corrosion-critical overlays in specialized applications.
• Surfacing overlays: Deposited strictly for abrasion or corrosion resistance rather than structural joining.

Aluminum is not realistic for SAW. The fluoride-borate flux chemistry is designed for ferrous metals, so aluminum fabrication is better left to other processes such as aluminum MIG welding.

Joint Designs and Thickness Range

SAW is commonly used for material from about 3/16 inch (5 mm) up to 5 inches (125 mm) thick, with its sweet spot between 1/2 inch and 5 inches. On high-speed pipe and strip lines, thin stock can be welded at over 100 in/min (about 2.5 m/min).

Joint preparation depends on thickness and deposition needs:

• Square or I-butt: For thinner plate requiring full penetration.
• Single V-groove: For moderate thickness, often with a backing strip.
• Double V or double bevel: For heavy plate, cutting filler volume and balancing distortion.
• Knife-edge bevel or U-groove: For very thick sections, minimizing deposited metal.

Single-wire SAW typically uses an included angle of about 45 degrees. With tandem or multiwire heads, a narrower groove of 25 to 30 degrees is often enough, as the trailing wires can reach the sidewalls.

Where SAW Reaches Its Limits

SAW is best suited to the flat and horizontal positions. It requires protection from wind to keep its flux pile intact, won’t follow contoured three-dimensional joints, and struggles out of position. For stock under about 3/16 inch, short intermittent welds, or tight field fit-up, processes like FCAW or SMAW are usually more practical. Simply put, when the job calls for long seams, thick plate, repeatable geometry, flat or horizontal, and shop conditions, SAW is at its most powerful.

SAW vs Other Welding Processes: An Honest Comparison

With so many arc welding methods to choose from, picking the right one for a job can be the difference between a profitable run and a costly setback. For heavy plate and long, straight seams, submerged arc welding (SAW) earns its keep. However, that does not make it a one-size-fits-all process. When measured against shielded metal arc welding (SMAW), gas metal arc welding (GMAW), and flux cored arc welding (FCAW), SAW trades flexibility for unmatched productivity and workplace comfort.

How Do These Processes Stack Up?

The most accurate way to judge a process is by its tradeoffs. No single method will top every category, as each has its place on the shop floor. Based on EPA AP-42 (1991) consumption figures, SMAW accounts for 45 percent of electrodes consumed, GMAW 34 percent, FCAW 17 percent and SAW 4 percent. This speaks more to SAW’s specialization for high-deposition work than its lack of capability. The following breakdown highlights where SAW shines and where it falls short:

Factor	SAW (Submerged Arc)	SMAW (Stick)	GMAW (MIG)	FCAW (Flux-Cored)
Deposition Rate	Highest (single-wire up to ~40 lb/h, tandem/multiwire over 100 lb/h)	Lowest (1–8 lb/h typical)	Moderate–high (5–12 lb/h)	High (6–15 lb/h, higher with certain wires)
Position Capability	Mostly flat and horizontal	All positions	Flat, horizontal, vertical, overhead (with skill)	All positions (with correct wire)
Fume & Arc Light	Minimal; EPA notes an extremely low fume formation rate	High fume and UV exposure	Moderate (shielding gas dependent)	High (especially in confined spaces)
Operator Skill	Low for manual input, high for setup/monitoring	High (arc control, electrode manipulation)	Moderate	Moderate–high out of position
Cost (Operational)	Lowest per lb for large runs	Highest per lb for volume	Moderate	Moderate
Penetration	Deep, consistent	Moderate, variable	Shallow–moderate	Moderate–deep
Joint Prep	Precise fit-up required	Forgiving	Moderate precision needed	More forgiving than GMAW

These differences are why shops still utilize versatile methods like stick welding (SMAW) for field repairs, while relying on SAW for long plate seams. For those looking to expand their skillset, an aluminium welding course can cover processes from aluminum MIG welding to aluminum flux core welding. Specialized work, such as alloy steel welding electrodes or all position welding rod selection, further showcases the flexibility of other processes.

When NOT to Use SAW

As AWS notes for the submerged arc process, its strengths are narrow by design. It is limited mostly to flat and horizontal positions, unlike SMAW or FCAW which work out of position. While semi-automatic hand-held SAW guns exist, the process is normally mechanized or automatic. This makes it ill-suited for tight corners, vertical seams, or one-off field repairs. Additionally, the flux blanket requires a controlled setup, so short, intermittent welds can be less economical. For jobs requiring mobility, consider methods like air arc welding and carbon arc gouging instead. If you’re working with small parts or exotic repairs, resources covering aluminum flux welding or alpha laser welding may be a better fit.

Ultimately, the choice isn’t about which process is “best”, but which one best serves your priorities. For shops focused on throughput, SAW is hard to beat. For those needing versatility in the field, the other arc processes will continue to hold their well-earned ground.

Common SAW Defects and How to Troubleshoot Them

One of the most unique aspects of submerged arc welding (SAW) is its lack of visibility. With the arc completely covered beneath a blanket of flux, operators are unable to watch the puddle in real time. As a result, the majority of defects go unnoticed until slag removal or formal inspection. This makes troubleshooting more reliant on prevention than reaction.

Porosity

Porosity is the trapping of gas pockets within the weld metal. Some of the most common causes include:

• Moisture: Damp flux introduces hydrogen and other gases into the weld pool.
• Contamination: Oils, rust, or mill scale on the joint can release gas during welding.
• Flux coverage: Insufficient coverage allows atmospheric gases to reach the molten puddle.
• Travel speed: Excessive speeds can prevent proper degassing of the weld metal.

According to The Fabricator’s troubleshooting column, inadequate flux coverage is especially prevalent on wide joints. To combat this, only use properly conditioned flux, thoroughly clean joint surfaces, maintain a consistent flux layer, and utilize a travel speed that allows gases to escape.

Lack of Fusion

While many assume amperage is to blame, lack of fusion in SAW is more often caused by an imbalance between deposition rate and travel speed. When too much weld metal is deposited too quickly, the puddle cannot properly wet the side walls or root, creating cold lapping. A strong indicator of this is centerline porosity on the second side of a two-sided joint, as it typically points to an unbonded root from the first pass.

As stated in the AWS Welding Digest, the solution lies in balancing heat input to travel speed and adjusting bead placement. This becomes especially critical when welding higher strength materials, such as those outlined in our Alloy Steel Welding Electrodes guide.

Slag Inclusion

Slag inclusions occur when solidified flux becomes trapped between passes or along the fusion line. Excessively convex beads often create tight valleys that are difficult to clean, while a viscous weld pool can prevent the slag from floating out. To prevent this, remove all slag between passes with a chipping hammer and wire brush, aim for a flatter bead profile, and adjust your parameters to promote a more fluid puddle.

Undercut

Undercut appears as a groove melted into the base metal adjacent to the weld toe without being filled with weld metal. In SAW, this is commonly caused by excessive arc voltage, high travel speed, or improper head positioning. Slightly lowering voltage, matching your travel speed to your deposition, or utilizing weaving techniques for wide joints will greatly reduce its occurrence.

Cracking (Hot and Hydrogen-Induced)

Cracking is the most structurally severe of all SAW defects. Excessive depth-to-width ratio is a major contributor, as deep and narrow single-pass beads create high restraint and rapid cooling. Other factors include thick plate restraint, high sulfur or phosphorus content, and moisture-laden consumables. For carbon steel applications, refer to the requirements of AWS A5.17/A5.17M (2025) to ensure compliance.

To mitigate these risks, utilize wider pass geometries when possible, store flux in heated cabinets, apply proper preheat based off of material and thickness, and control hydrogen levels. For more foundational knowledge, review AWS’s Submerged Arc Welding handbook.

Arc Instability and Bead Shape Problems

Erratic whistling, wandering beads, or inconsistent penetration are often linked to worn drive rolls, incorrect wire stick-out, poor electrical connections, or an undersized power source. Ropy, humped, or excessively wide beads are typically caused by an imbalance of wire feed speed, voltage, and travel speed. For tuning assistance, utilize a parameter chart specific to your wire and flux combination and keep head alignment consistent. More practical advice can be found through Canadian Metalworking’s SAW tech tips.

Safety, Health and Environmental Aspects of SAW

Submerged arc welding has a reputation as one of the calmest processes in a heavy fabrication shop, and much of it is earned. With the arc buried under granular flux there is no visible flash, almost no spatter, and far less crackle than an open-arc booth. Calmer does not mean hazard-free. The risks simply shift, away from the arc and toward fume, heat, hot slag, dust and the byproducts nobody notices until exposure has already happened.

What the Flux Blanket Does and Doesn’t Shield You From

The flux blanket suppresses most arc radiation, sparks and spatter, which is why SAW stations look friendlier than a stick or MIG booth. That suppression is real but partial. Radiation escapes during arc initiation, wherever the weld head runs short of flux, at the edges of a long groove, or when an operator strikes an arc outside the flux pile. Ultraviolet and infrared energy still reach surrounding workers, so screens, curtain barriers and correct helmet shade selection stay mandatory rather than optional. Heat is a separate issue: molten slag sits on the bead long after the arc has passed, holding temperature well into post-weld cleanup and spitting or cracking unpredictably when disturbed. The practical rule is that a buried arc is a partially shielded arc, not an unprotected one, and everyone in the bay still needs the eye, skin and respiratory protection they would use on an open-arc process, as the AWS submerged arc welding handbook makes clear.

Welding Fume: The Hazard You Cannot See

Fume is the health issue that deserves the most attention in SAW. The OSHA welding fact sheet lists the metals commonly present in welding fume, including manganese, chromium, nickel and lead, alongside gases such as nitrogen oxides, carbon monoxide and ozone. Which of those you breathe depends on the base metal, the wire and flux chemistry, and how much fume escapes the blanket. Welding on stainless or alloy steels raises hexavalent chromium and nickel concerns, one more reason to choose consumables with full awareness of what they put into the air; our guide to alloy steel welding electrodes covers that selection side in detail.

The regulatory baseline matters. The International Agency for Research on Cancer classifies welding fumes as Group 1 carcinogens, and ultraviolet radiation from welding processes is likewise Group 1. OSHA’s standard for hexavalent chromium, 29 CFR 1910.1026, sets a permissible exposure limit of 5 micrograms per cubic meter averaged over an eight-hour shift, with an action level half that. Because welding fume is a mixture rather than a single substance, that Cr(VI) limit works alongside OSHA’s general particulate limits, and both are exceeded quickly in an unventilated shop running continuous SAW beads.

The Ventilation Hierarchy in Practice

Controls should follow a hierarchy rather than a grab-bag of afterthoughts:

1. Engineering controls first. Capture fume at the source with a local exhaust hood or extractor positioned near the weld head, or enclose the station entirely on automated gantries. Fixed enclosures with filtered exhaust beat portable arms on long, continuous seams.
2. Administrative controls second. Rotate operators, schedule heavy welding in better-ventilated bays, and keep people out of the plume zone during long runs.
3. PPE last, but never skipped. Respirators selected and fit-tested under OSHA’s respiratory protection rules, helmets with the correct lens shade, flame-resistant clothing, gauntlets and hearing protection.

Flux, Slag and Confined Space Hazards

Flux and slag bring their own handling discipline. Fresh flux is a fine dust that irritates skin and airways, so pour it from a controlled height, keep bags closed and wash thoroughly after handling. Unused flux recovered by the vacuum system should be screened before it goes back into the hopper; tramp metal, slag chips and moisture in the recovery line cause arc instability and porosity later. Spent flux and slag come off the bead extremely hot, can crack or spatter when chipped, and belong in dry metal containers rather than swept wet or dumped into drains. Some flux chemistries contain fluoride or borate compounds, so disposal sits in your waste plan, not the floor drain.

Confined spaces raise everything an order of magnitude. A tank, vessel or closed girder box requires a formal permit-entry program with atmospheric testing for oxygen deficiency, carbon monoxide and metal fume, plus continuous forced ventilation and a dedicated attendant. Damp or poorly stored basic flux also pushes hydrogen into the weld and invites cracking, which is why keeping flux dry and sealed is a safety control as much as a quality one. Related hot-work hazards, including gouging and back-gouging often used to sound out SAW roots, are covered in our guide to air arc welding and carbon arc gouging.

Recommended Controls Checklist

• Position source-capture exhaust at the weld head before adding general room ventilation.
• Monitor exposure against the 5 µg/m³ Cr(VI) limit and track it with periodic air sampling.
• Store flux sealed, dry and off the floor, and screen recovered flux before reuse.
• Let slag cool before chipping, and collect it in covered, dry containers.
• Use permit-required confined space procedures for any enclosed weldment.
• Train every operator to treat the flux blanket as partial shielding, not full protection.

Handled this way, SAW keeps its genuine safety advantage: fewer arc flashes, minimal spatter and less operator fatigue, paired with the industrial hygiene controls a high-deposition process genuinely requires. The AWS practical guide to submerged arc welding and workplace safety references such as SAIF’s welding health and safety document reinforce the same point: the process rewards shops that plan ventilation and handling before the first arc, not after the inspection report.

Practical Tips, Common Mistakes and Key Takeaways

Most SAW problems are not caused by the arc itself. They are caused by the small, unglamorous decisions made before the arc is struck: how tight the fit-up is, what electrode went into the tack, how damp the flux got overnight, where the head sits on a pipe. Below is a shop-ready checklist drawn from common troubleshooting columns, including published guidance on lack of fusion and porosity in submerged arc work.

The Pre-Weld Checklist

• Hold fit-up tolerance tight. Root openings and land variations show up directly as lack of fusion or a wandering bead. Straighten and re-fit before you clamp, not after.
• Choose tack electrodes carefully. Tacks that are porous or hydrogen-rich become the seed for porosity and cracking in the final pass. Recommended tack electrodes for sub arc joints include E6010, E6011, E7015, E7016 and E7018 types, ground smooth where the SAW bead will cover them.
• Store flux dry and screen it. Flux is a chemical product, not gravel. Keep bags off the floor, re-cover opened containers, and never dump reclaimed flux back into the hopper raw.
• Set parameters from a written procedure. Guessing wire feed speed and arc voltage is the fastest route to a bead shape nobody can explain. Write the numbers down and stay within them.

Setup Details That Decide Bead Quality

On circumferential welds, head offset from top dead center is a common but under-appreciated variable. Too much offset, or too little, changes how the molten pool sits relative to the flux and the joint. The result is the classic pairing: irregular bead profile plus molten flux spilling out of the seam. Small offset corrections usually fix both symptoms at once.

Recovery deserves the same discipline. Vacuum-recovered flux goes through a screening step before reuse because particle size degrades with handling. Excessive fines change the blanket’s permeability and insulation, and the symptom they produce is porosity buried under a bead that looked perfectly normal going in. Screen it, mix recovered flux with fresh at a sensible ratio, and discard anything that looks chalky or contaminated with slag chips.

Common Mistakes, Quick Fixes

Mistake	What you see	Fix
Skipping interpass slag removal	Slag inclusions, repair grinding	Chip and wire-brush between passes, every time
Running wet or unscreened flux	Porosity, spatter, erratic arc	Dry storage, screen reclaimed flux, limit reuse ratio
Wrong stick-out (CTTW)	Excessive penetration or cold lap	Return to procedure length and hold it
Tack welds left proud and dirty	Crater cracks carried into the seam	Use low-hydrogen tacks, blend smooth
Bead overlap by eye alone	Uneven reinforcement, overlap defects	Set overlap by width measurement and travel speed
Untuned arc on each new joint	Unstable arc, inconsistent shape	Re-check voltage and feed at start of every run

Training and Skill Transfer

SAW has a reputation as a low-skill process because the arc is hidden and the machine moves itself. That is only half true. Machine tending, joint prep, flux management and troubleshooting are real skills, and shops that skip formal training pay for it in radiographic rejects. Welders coming from stick work often transfer faster than expected, since the fundamentals of heat input and bead shape carry over. If your team is building out core competency, it helps to start with a structured all position welding rod guide for the SMAW side, then layer SAW procedure training on top. Electrode knowledge also transfers: understanding alloy steel welding electrodes makes AWS A5.23 filler selection far less intimidating.

Supplies matter too. A well-stocked, reliably sourced consumables pipeline keeps flux, wire and drive rolls consistent from job to job; a practical Airgas welding supplies overview shows what a production welding inventory normally includes.

Key Takeaways

1. Sub arc welding earns its place on long, heavy, flat or horizontal butt joints where deposition rate, deep penetration and low spatter decide the schedule.
2. It is the wrong tool for out-of-position work, thin sheet, short runs and field repairs. For those, stick is often the better answer, as explained in advantages of stick welding.
3. Quality is decided mostly before the arc: fit-up, clean dry flux, written parameters, correct head position and disciplined interpass cleaning.
4. Inspect what you cannot see. Slag-covered beads hide porosity and lack of fusion until NDT finds them.
5. Protect the crew: proper ventilation, shielding, fume controls and confined-space procedures are non-negotiable.

If your work involves thick carbon or low-alloy plate, long seams, high deposition and repeatable procedures, sub arc welding is still one of the most economical processes in steel fabrication. Choose it for the joints it was built for, keep flux and parameters under control, and inspect honestly. Do that, and the hidden arc keeps doing what it has done since 1935: weld heavy steel fast, quietly and consistently.

Frequently Asked Questions

What is sub arc welding?

Sub arc welding, more properly called submerged arc welding (SAW), is an arc welding process in which the arc and molten weld pool are buried under a blanket of granular fusible flux. The flux shields the weld from air, melts into a protective slag, and lets the process run at very high deposition rates with almost no spatter or arc flash.

Why is it called submerged arc welding?

The arc is submerged because a layer of granular flux covers it completely, so you never see the arc during normal operation. Cold flux does not conduct electricity, so the arc starts under the flux blanket and is then maintained through the molten, now conductive, flux.

What materials can SAW weld?

SAW is mainly used on carbon steels, low alloy steels, stainless steels and some nickel-based alloys, plus surfacing and hardfacing overlays. It is essentially a ferrous-process, which is one of its main limitations compared with GMAW or SMAW.

What welding positions does sub arc welding allow?

Because the flux must stay on the joint, SAW is normally restricted to the flat and horizontal-fillet positions, such as 1G and 1F, with 2F sometimes possible. Horizontal groove welds have been done with special flux-support arrangements, but out-of-position work is not practical.

How fast can submerged arc welding deposit metal?

Single-wire SAW systems typically reach deposition rates up to about 40 lb/h (18 kg/h), while tandem and multiwire setups can exceed 100 lb/h (45 kg/h). By comparison, stick welding tops out near 10 lb/h (5 kg/h).

What is the difference between SAW and SMAW?

SAW uses a bare continuously fed wire under granular flux and is mechanized or automatic, giving deep penetration, smooth beads and very low fume and arc light. SMAW uses a coated stick electrode that the welder manipulates by hand, works in any position, but deposits metal far more slowly.

What are the most common SAW defects?

The frequent ones are porosity from damp flux or contaminated joints, lack of fusion from wrong parameters or joint fit-up, slag inclusion from incomplete interpass cleaning, undercut from excessive travel speed, and hydrogen or solidification cracking. Because the arc is hidden, these usually show up only at inspection.

Is submerged arc welding safe?

SAW is relatively gentle on the operator because the flux blanket blocks most ultraviolet radiation, spatter and fume, but hazards remain: flux dust, slag handling, hot metal, and residual fume containing manganese, chromium and nickel. Welding fume and UV are classified by IARC as Group 1 carcinogens, so ventilation, PPE and exposure monitoring are still required.

Can flux be reused in SAW?

Yes, typically 50 to 90 percent of the granular flux is recovered, screened and reused. Flux that has actually melted into slag cannot be reused, and recovered flux contaminated with fines, moisture or slag must be discarded or reconditioned in an oven.

When should you not use sub arc welding?

Avoid SAW for out-of-position welds, short intermittent joints, field repairs and non-ferrous metals. It is also a poor fit for thin, heat-sensitive assemblies unless travel speed and heat input are carefully controlled to prevent burn-through.