Submerged arc welding is a welding method in which an arc burns under a layer of flux. Its inherent advantages such as stable welding quality, high welding productivity, no arc light and little smoke make it the main welding method in the manufacture of important steel structures such as pressure vessels, pipe section manufacturing (such as SSAW pipe and LSAW pipe ), and box-shaped beams and columns.1. High production efficiencyThis is because, on the one hand, the conductive length of the welding wire is shortened, and the current and current density are increased, so the penetration depth of the arc and the deposition efficiency of the welding wire are greatly improved. On the other hand, due to the heat insulation effect of flux and slag, there is basically no heat radiation loss on the arc, and there is less spatter. Although the heat loss for melting flux increases, the overall thermal efficiency is still greatly increased.2. High weld qualityThe slag has a good protective effect in insulating the air, the welding parameters can be kept stable through automatic adjustment, the technical level of the welder is not high, the weld composition is stable, and the mechanical properties are relatively good.3. Good working conditionsIn addition to reducing the labor intensity of manual welding operations, it has no arc radiation, which is a unique advantage of submerged arc welding.1. Submerged arc welding is protected by granular flux, which is generally only suitable for welding in flat welding and fillet welding positions. For welding at other positions, special devices are required to ensure that the flux covers the weld area and prevent leakage of molten pool metal.2. The relative position of the arc and the groove cannot be directly observed during welding, and an automatic welding seam tracking device is required to ensure that the welding torch is aligned with the welding seam without welding deviation.3. Submerged arc welding uses a large current, and the electric field strength of the arc is high. When the current is less than 100A, the arc stability is poor, so it is not suitable for welding thin-walled pipes.
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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 (see Figure 1). If you are thinking about using SAW, consider the numerous factors that affect process success. Material thickness, 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 upfront, but the investment can yield a significant and quick return in many cases.
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 raises 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.
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 applications can achieve significant deposition rates (see Figure 2), depending on wire size, type, and polarity. It can be quite easy to use SAW to improve deposition rates over a current GMAW, flux-cored arc welding (FCAW), or shielded metal arc welding (SMAW, or stick) process. Welding equipment and filler metal manufacturers can assist you in determining starting parameters and provide insight on improvement potential.
In addition to productivity gains, the process 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.
The process also offers an improved working environment because it has low fume generation and no visible arc. This minimizes UV exposure, so you 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.
Last, SAW produces excellent mechanical properties in the finished weld. Many medium- to high-basicity wire/flux combinations can 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.
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, the process typically has a higher capital investment than other processes.
To help optimize mechanization'and to provide varying levels of flexibility depending on application needs'numerous accessories are 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:
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 this process, 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.
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However, keep in mind that this process is limited to flat and horizontal position welding, which allows the use of high-current and high-deposition parameters. Using SAW for entire weldments with multiple welds may require large positioning equipment; several options include drop-tilt, headstock, and tailstock setups. Sometimes this positioning equipment can be cost-prohibitive, but in other cases the return on investment can quickly justify it and the process compared to welding out of position with another process.
Also, because you 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 a SAW operation.
Several factors 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 SAW of thick materials is the most common, it is a misconception that the process can be used only 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-mm material in a single pass at 800 amps with a travel speed of 76.2 cm 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 choice for improved repeatability.
Regardless of material thickness, key part considerations for successful SAW implementation include the following:
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 they 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 also can 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 multipass welding, depending on material thickness 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).
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.
Photos courtesy of Miller Electric Mfg. Co.
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