Can quality meet quantity? It sure can. The submerged arc welding process (SAW) is a specialized metal joining method applied when you need to weld extreme thicknesses and achieve exceptional weld quality. It offers an extremely high metal deposition rate while providing high weld accuracy, fusion quality, depth of penetration, and a low rate of weld discontinuities.
Other highly efficient arc welding processes, like MIG and Flux-cored, can’t match the deposition rate of the submerged arc welders. Heavy fabrication of structural steel, shipbuilding, and pressure vessels relies on the SAW to meet the production demand and quality expectations.
What Is Submerged Arc Welding?
Submerged arc welding is an arc-based welding process with a defining characteristic — the arc melts and fuses the filler wire (electrode) under a large amount of crushed flux. Other arc welding processes rely on a shielding gas (MIG/TIG) or a protective flux bound externally or internally to the electrode (stick/flux-cored). But, with SAW, the flux is independent of the electrode, while the electrode is, quite literally, submerged in it.
Quick SAW Factsheet:
- Extreme deposition rate, especially when used in multi-wire mode. Single-wire SAW can deposit up to 40 pounds of filler metal per hour, while multi-wire systems can achieve more than 100 pounds of metal deposition per hour. No other arc welding process can accomplish the same.
- Produces clean, uniform welds.
- Exceptional weld penetration, even on the thickest materials.
- Can weld extreme thicknesses in single or multi-pass configurations.
- Utilizes AC or DC with constant current (CC) or constant voltage (CV) power sources.
- Usually used as an automated or mechanized process.
- Arc is submerged and not visible, which reduces workplace hazards.
- Welds most carbon and alloy steels and nickel alloys.
How Submerged Arc Welding Works?
“You can use SAW with a single electrode or run it in a multi-wire system for a drastic boost in deposition rate”
Submerged arc welding works by forming an arc between a wire electrode and the welded workpiece. The ground connection completes the electrical circuit between the electrode and the power source, while the resistance to the flow of current melts the electrode and the welded metal. In other words, the fundamental principle of SAW operation is exactly the same as any other arc welding process.
However, SAW has many differences on the operational level compared to other arc processes. The flux burying the electrode protects the weld puddle from atmospheric contamination and can influence the weld alloy chemistry and the resulting weld quality. Likewise, the flux covering the arc prevents the UV/IR arc worker exposure and the welding fumes and sparks are minimized. So, SAW is much safer than other arc welding processes.
You can use SAW with a single electrode or run it in a multi-wire system for a drastic boost in deposition rate. This process is flexible with numerous wire feeding setups, including hot and cold wires that can be fed into the joint or into the edge of the weld pool. You can even replace the wire with a metal strip, which benefits some applications like hardfacing.
While flexible in flux/wire configurations, SAW is limited to horizontal and flat welding positions. The weld puddle is too fluid for vertical and overhead applications. But, using positioners, welding manipulators, and other automated welding equipment, you can configure SAW for most heavy fabrication.
SAW is almost always used in an automated or mechanized welding system. While manual SAW application is possible, it’s not the norm in the industry. SAW is not the most viable solution for short welds. It’s the most cost-effective and productivity-boosting when applied to a batch of long circumferential or longitudinal welds.
The SAW Power Source
The choice of a power source can easily make or break any welding process, including SAW. But, this is particularly the case with SAW as this is a highly demanding process that requires maximum machine reliability.
SAW is performed at high amperages in heavy fabrication. Subarc welders can have over 1000A of power and output AC and DC. For example, the Miller SubArc Digital 1000 can output AC and DC in single or multi-wire configuration at 1000A with a 100% duty cycle. Going back to the issue of reliability, running SAW at such high amperages for continuous heavy fabrication can be troublesome as the equipment can break down. This is why it’s important to invest in high-end brands. Miller’s SubArc Digital Series has a highly reliable thyristor power regulation, which is a solid-state technology that improves reliability and stability.
You can also benefit from power sources with advanced waveform control. The prime example is the Lincoln Electric Power Wave AC/DC 1000 SAW machine with Lincoln’s Waveform Control Technology. You can control and shape the arc’s waveform to adapt to almost any application. The Waveform Control Technology lets you control the wire feed speed, current, voltage, wave frequency, variable balance, DC offset, phase relationship (to control arc blow), and other settings that aren’t usually available with SAW. Lincoln’s technology modernized this welding process, allowing you to fully experience the benefits of single and tandem-wire SAW welding.
It’s critical to highlight that power source selection also depends on how many wires you plan to run and at what polarity/current type. For example, the before mentioned Miller’s and Lincoln’s SAW machines can output AC and DC in tandem welding modes, allowing you to weld with a leading wire using the DC (DCEN higher deposition / DCEP higher penetration) and a trailing wire with AC (to prevent arc blow).
Tandem or multi-wire welding can dramatically boost productivity and improve your ROI. So, this is a crucial aspect of SAW that should be exploited as much as your application allows it. In tandem arc welding, the leading wire penetrates the material, while the trailing wire does the fill and cap. This is an extremely powerful concept when used appropriately and can help you significantly improve the production time compared to standard SAW, MIG, and flux-cored.
However, there are many variables when it comes to choosing a SAW machine, especially in heavy fabrication. We offer rugged, sophisticated, reliable, and specialized SAW power sources. Each machine can be the “best,” depending on many factors. If you aren’t sure which SAW power source is the most suitable for you, reach out and our experts will assist you in no time.
The Role Of Flux
There is a large number of flux types for SAW. They all have distinctive purposes. But, all SAW fluxes have the primary objective: to protect the weld pool from atmospheric contamination. The flux in direct contact with the molten metal melts and solidifies into a protective slag, just like slag produced by stick welding. However, this is just a small amount of flux that interacts with the molten pool in this way, while the rest of the flux can be captured and re-used. This slag must be chipped/peeled off before any subsequent weld passes are made.
Flux can also perform the following:
- Stabilize the arc.
- Control slag viscosity and freezing range.
- Modify the chemical composition of the weld. Some fluxes include the alloying elements, which are critical for some applications. Voltage control can modify the amount of melted flux and the resulting alloy deposition in the weld.
- Influence the shape of the weld bead.
- Alter the weld mechanical properties.
American Welding Society (AWS A5.17 and A5.23) classifies SAW fluxes as:
- Neutral fluxes – don’t make significant changes to the weld metal. They are a good general-purpose flux type, especially for multi-pass welding when it is important to limit alloy buildup.
- Active fluxes – contain manganese, silicon, or both to improve resistance to contamination. They are generally used for single-pass welds, but they can alter the weld properties as a result of voltage output changes.
- Alloy fluxes – are formulated with alloys and can alter the chemistry of the weld. They are often used to make alloyed weld deposition when using plain carbon steel wires. To modify the rate of alloy addition, you can increase/decrease the arc’s voltage, which controls how much flux is melted. This requires a precise voltage output control, which is again where high-end SAW power sources come to the rescue.
SAW Wires
SAW wires are very similar to MIG wires. They can be solid or cored and contain alloying elements for improving the weld quality. Likewise, they are often copper-coated for better conductivity and preventing oxidation. In fact, the only visible difference between SAW and MIG wires is their thickness, as SAW wires often have much higher diameters. There is a large number of SAW wires you can use, depending on the welded metal and the desired outcome.
It’s recommended to observe the SAW wire and flux as a combination. So, choosing one without considering the effect of the other is not a good idea. Wire/flux combinations are used to get the precise weld results you want, control the hydrogen level, modify the weld alloy, and achieve the desired mechanical properties of the weld.
Submerged Arc Welding Applications In Heavy Fabrication
SAW is primarily used to join thick materials and achieve a high deposition rate and weld penetration. However, SAW can also be used to join relatively thin metals with a very high welding speed. But, let’s stick to heavy fabrication in this article and see how SAW benefits fabricators working with thick metal.
You can use SAW to weld carbon steel, stainless steel, low-alloy steel, chrome-moly, and nickel-based alloys.
Structural Welding
SAW is an excellent welding process for fabricating massive beams, frames, trusses, piles, and other critical structural members of large buildings and bridges.
Such projects often require a series of customized structural elements that must be produced to meet the specification requirement, which is where fab shops come in. Fabricators use automated or mechanized SAW equipment to produce lengthy longitudinal welds to join structural steel plates into structural members like beams.
Longitudinal seam welders and welding manipulators equipped with a subarc welding head are a great choice for automatic structural welding. These automated systems can guide the welding head along the seam of two flat plates to produce beams, trusses, and other structural members. Likewise, a longitudinal seam welder can produce a seam weld to join rolled plates into piles and other cylindrical structural pieces. These systems are easy to set up and reduce the requirement for skilled labor, while achieving maximum productivity and weld quality.
Shipbuilding
Welding in shipbuilding is primarily performed using MIG, Flux-cored, and SAW welding, thanks to their high efficiency and ease of use. But, fabricating heavy ship framing, girders, hulls, and decks benefits the most from SAW as it provides the highest deposition rate and weld penetration.
Fabrication of almost all structural ship parts can be automated with SAW with the benefit of improved productivity over MIG and Flux-cored. However, the process selection comes down to many variables for Shipyards, including operator training and whether the job is performed inside the shop or in the open shipyard.
Pressure Vessel Welding
What do almost all pressure vessels have in common? A massive amount of stored energy, which can be released all at once if the welds were to fail, resulting in dangerous explosions. So, regardless of the industry and the stored/processed contents inside them, all pressure vessels must be welded according to strict codes and standards.
Like with other applications, SAW can be used in tandem with TIG, MIG, Flux-cored, and MMA for various weld passes when fabricating pressure vessels. However, SAW provides the highest deposition rate and penetration, making it the most productive welding process for heavy wall ASME pressure vessel production.
A particular benefit of SAW for pressure vessels with extreme wall thicknesses is the ability to weld with narrow root openings, also referred to as narrow gap welding. This reduces the required filler metal deposition and the time it takes to weld the joint, making the process less costly and more efficient.
Before welding, rolled plates need to be aligned for a butt weld, which is a job for specialized fit-up bed rollers. These stations rotate and translate the rolled plates for maximum joint alignment before the mechanized can lay a seam weld using a SAW welding process. Positioners and welding turning rolls can be used for automated and controlled pressure vessel rotation while the welding manipulator completes circumferential SAW welds.
Offshore Structure Welding
Welding offshore structures benefits from SAW because the foundations and other critical structural offshore elements have high thicknesses. In particular, offshore oil rigs and wind farms require massive structural steel piles, towers, beams, jacket structures, and jack-up legs. All of which should be SAW welded to achieve high productivity.
Like pressure vessels and structural welding applications, offshore welding productivity can experience a significant boost from automated welding equipment. Pairing positioners, turning rolls, longitudinal welders, and manipulators with a subarc welding system boosts productivity and reduces the rework. Automatization requires less skilled labor and makes the job more streamlined, predictable, and modular, while SAW ensures exceptional penetration and weld quality.
An excellent testament to the possible SAW productivity when done right is the job Red-D-Arc fulfilled for a construction company from Willebroek (Belgium). We delivered manipulators equipped with a double-wire system for the construction of an offshore wind farm close to the German-Dutch border, and each turnkey system only required a single operator.
One particular automatization system for offshore is the growing line system. Quite literally, this system grows in size to accommodate wind tower bodies and piles as they are extended with cans welded one to another. Wind towers can’t be produced in one piece. They are usually welded from individual cans, but this requires a system that supports the individual pieces and grows in length, while a welding manipulator uses a SAW head to join them together.
Rent or Lease From Red-D-Arc
SAW is an incredible welding process that’s only been improved since its inception in 1935, and we have some of the most advanced subarc power sources, flux recovery systems, SAW tractors, and the weld automatization equipment to go with it. Whether your application requires SAW, or GMAW, GTAW, FCAW, or SMAW, we have the equipment you need to achieve your productivity goals and improve your bottom line.
Contact us today, and our team of experts will work with you to find the most optimal welding process and equipment for your industry and specific application.
