Why is submerged arc welding better?

Sep. 23, 2024

Is Submerged Arc Welding the Right Process for You?

By: Hobart Brothers

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Companies thinking of making a change to the SAW process should consider the benefits it offers, as well as some factors that make it a good fit for a specific application, to help get the most from the investment. (Photo courtesy of Miller Electric Mfg. Co.)

The submerged arc welding (SAW) process has the potential to substantially improve deposition rates and productivity, and to provide repeatable weld quality. However, it is better suited for some applications than others. When considering SAW, there are numerous factors that can affect process success. Material thickness, along with joint design, fit-up and length all need to be assessed.

Also, be aware that achieving maximum success with SAW requires some homework and an investment in equipment up front &#; but it can yield a significant and quick return in many cases.

How does SAW work?
SAW is a wire-fed process, like gas metal arc welding (GMAW, or MIG). Wire is fed through a torch that typically moves along the weld joint by mechanization. Understanding and controlling SAW is not significantly different than understanding and controlling GMAW. Setting the machine is similar, and many welding variables remain the same: Voltage still influences bead width, amperage still influences penetration, and increasing wire feed speed still increases amperage and deposition (assuming constant contact-to-work distance and use of a CV power supply).

Unlike GMAW, SAW relies on granular flux to protect the arc from the atmosphere. The arc is buried &#; submerged &#; in the flux and is not visible during normal operation. As the arc melts the wire, flux and base material to form the weld pool, the molten flux performs important functions such as deoxidizing, alloying, shaping and generating a protective atmosphere for the weld deposit.

Single-wire SAW applications can achieve deposition rates of up to 40 pounds per hour, depending on wire size, type and polarity. (Photo courtesy of Miller Electric Mfg. Co.)

What can be gained with SAW?
An optimized SAW process can provide gains in throughput, time savings, weld quality and consistency, as well as an improved environment for the operator.

Single-wire SAW applications can achieve deposition rates of up to 18 kilograms per hour, depending on wire size, type and polarity. While achieving this value is not typical for most applications, it can be quite easy to use SAW to improve deposition rates over a current GMAW, flux-cored arc welding (FCAW) or stick metal arc welding (SMAW) process. Welding equipment and filler metal manufacturers can assist in determining starting parameters and provide insight on improvement potential.

In addition to productivity gains, SAW can provide repeatable weld quality. SAW is almost exclusively a mechanized process. The arc and/or work-motion machinery maintains consistent travel speeds and torch positioning, so operators with less hands-on welding experience can easily oversee it. Companies can then allocate their most skilled personnel in the most demanding areas of the operation.

SAW also offers an improved working environment because it has low fume generation and no visible arc. This minimizes UV exposure, so operators do not need to wear a helmet or welding jacket, and it&#;s easier for other tasks to occur near the welding operation in progress.

Lastly, excellent mechanical properties of the finished weld are another benefit of SAW. Many medium- to high-basicity wire/flux combinations can easily obtain high toughness &#; even at or below -60 degrees Celsius, which can be difficult even for well-designed, rutile-based FCAW wires. Certain SAW wires and fluxes can also help maintain properties at high-heat inputs, further optimizing potential deposition rates.

What equipment is needed for effective SAW?
SAW can offer substantial productivity gains in certain applications, but achieving those results requires investing in the proper equipment, in addition to the power supply and wire feeder. Therefore, SAW typically has a higher capital investment than other processes.

To help optimize SAW mechanization &#; and to provide varying levels of flexibility depending on application needs &#; there are numerous accessories available.

In some applications, the torch is kept stationary and the workpiece is moved using positioning equipment. When arc motion is required, there are several options:

SAW welding tractors offer portability and flexibility for bringing welding to jobs located throughout the shop or perhaps inside a vessel.
Side beams or gantry setupsare not portable but instead are a fixed installation, requiring work to be brought to the weld cell. This reduces time spent on setup/changeover, but also reduces flexibility.
An integrator can help design a custom system, such as girth welding for storage vessels or circular welders for attaching nozzles. Some solutions can be integrated with positioning equipment to weld more complex geometry such as pipe saddles.

Compared to robotic welding, SAW mechanization is much more accessible. It&#;s typically simpler to implement and become familiar with. Although operator attention is required with SAW, it&#;s often easier to adjust during welding compared to a robotic welding operation. In addition, SAW equipment is generally designed for ruggedness and reliability.

However, keep in mind that SAW is limited to flat and horizontal position welding, which allows the use of high-current/high-deposition welding parameters. Using SAW for entire weldments with multiple welds may require large positioning equipment; several options include drop-tilt, head and tailstock. Sometimes this positioning equipment can be cost-prohibitive, but in other cases the return on investment can quickly justify it and the SAW process compared to welding out of position with another process.

Also, because operators cannot see the arc&#;s position during welding, joint tracking equipment may be needed. Options range from simple, such as a laser that indicates the future position of the welding arc, to more complex, such as a tactile probe that can automatically adjust torch position.

Consult with an integrator or equipment manufacturer to determine the combination of equipment to maximize the potential and determine the ROI of an SAW operation.

SAW welding tractors offer portability and flexibility for bringing welding to jobs located throughout the shop or perhaps inside a vessel. (Photo courtesy of Miller Electric Mfg. Co.)

What parts can be effectively welded using SAW?
There are several factors that make a part right for SAW. Material type and thickness are two important considerations.

SAW is best suited for carbon and low-alloy steels, but it can be used for stainless steel and nickel-based alloys as well. And while thick materials are the most common, it is a misconception that SAW can only be used on thick materials.

SAW is used successfully on thin materials in many applications, such as propane tanks and water heaters. Although high amperages are used, the travel speed increases significantly in these cases so that the resulting heat input is low. For example, single-torch SAW can be used to weld 6.5-millimeter material in a single pass at 800 amps with a travel speed of 76.2 centimeters per minute (or more, depending on joint design). Note that welding thinner materials also requires greater attention to the &#;smoothness&#; of the mechanization, joint tracking and consistency of joint preparation. Joint backing using copper and/or welding flux is a popular solution for improved repeatability.

Regardless of material thickness, key part considerations for successful SAW implementation include the following:

Joint and part geometries: SAW is suited to straight-line joints, since parts with jogs in the weld require more complex and expensive mechanization to handle repeatedly. And while SAW is well-suited for high-volume components, that doesn&#;t mean it can only be used for the exact same part over and over. Even job shops can take advantage of SAW. Parts don&#;t need to be identical, but they should have similar geometries to maximize the process. For example, it&#;s common for SAW and its equipment to easily weld both 3.7-meter-diameter and 3-meter-diameter pressure vessels since the geometries are similar. The idea is to find parts that can utilize the same arc/work motion equipment and equipment placement to minimize changeover and, therefore, downtime.
Long weld joints: A disadvantage of SAW is the required interpass cleaning. For this reason, it&#;s better suited to long weld joints (often 1.2 meters or longer), which can be cleaned during welding. With shorter welds, the total amount of time spent cleaning is greater because multi-tasking is more difficult, and the ratio of arc-on time versus time spent repositioning/readjusting equipment becomes smaller. As a side note, it is also important to consider investing in flux recovery and reconditioning equipment (a vacuum and oven) to minimize consumable costs.
Circumferential welds larger than 200 millimeters in diameter: SAW is a popular choice in pressure vessel and pipe applications, because the vessel or pipe can be rotated on positioners. But below this diameter, flux containment becomes more difficult because the flux waterfalls off the pipe. Because the weld cooling rate in SAW is slower than other processes, using it on smaller-diameter pipe can also result in an unacceptable bead profile.
Parts with good access: SAW equipment is bulky, which make space and part access key considerations. A system may need to be custom-designed for use in smaller spaces, but wire feeding may become an issue. The large diameters simply aren&#;t as flexible as the small diameters used on a robotic GMAW arm.

Joint design considerations
Good part fit-up is necessary for successful SAW &#; otherwise there could be a problem with burn-through. These issues must be compensated for prior to the welding process, and may require mechanical fixturing and special attention to part preparation.

&#;Seal beads&#; made using GMAW, FCAW or SMAW can be used to help compensate for less-than-ideal fit-up. These quick extra weld passes add time to the operation, but are often less time-consuming than if the entire joint was welded with a process other than SAW.

Potential problems can also be solved by reconsidering the joint. The deep penetration of the SAW process may allow root faces to be increased &#; or joint preparation to be eliminated entirely.

It may still be necessary to perform multi-pass welding, depending on material thickness and/or mechanical properties desired for the application. This approach can be better than significantly increasing heat to complete a weld in a single pass. Even though high amperages lead to higher deposition rates, SAW is not infinitely tolerant of heat input (a common misconception).

Considering the ROI of SAW
The SAW process can provide significant advantages for productivity and quality in the right application. However, it&#;s important to have a good understanding of what the process involves &#; and make sure your specific application is well-suited to SAW &#; before making the investment.

Integrators and equipment manufacturers can offer help in design and implementation of an optimized SAW process, or advise when SAW may not be the right process. In certain applications, the impact on the bottom line can be significant.

The Role of Submerged Arc Welding in Heavy Fabrication

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 A of power and output AC and DC. For example, the Miller SubArc Digital can output AC and DC in single or multi-wire configuration at A 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 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.

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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 , 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.

Red-D-Arc, an Airgas company, rents and leases welders, welding positioners, welding-related equipment, and electric power generators &#; anywhere in the world. Our rental welders, positioners and specialty products have been engineered and built to provide Extreme-Duty&#; performance and reliability in even the harshest environments, and are available through over 70 Red-D-Arc Service Centers, strategically located throughout the United States, Canada, the United Kingdom, France, and the Netherlands, as well as through strategic alliances in the Middle East, Spain, Italy, Croatia, and the Caribbean. From our rental fleet of over 60,000 welders, 3,700 weld positioners, and 3,700 electric-power generators, we can supply you with the equipment you need &#; where you need it &#; when you need it.