The SAW process is commonly used in demanding heavy industrial applications in industries such as pressure vessel, wind tower and rail car fabrication, shipbuilding and offshore oil rig welding. But the characteristics of SAW can be beneficial in a wide variety of applications, especially those that require high productivity rates.
The biggest advantage of Submerged Arc welding is the high deposition rate that can be achieved, which can have a significant impact on productivity and efficiency. Because this process is typically automated to some degree, consistent quality welds are easily achieved. In addition, there is a level of operator comfort and safety added as well, due to the SAW characteristics of low fume and no open arc.
Understanding the benefits of the process — and the applications for which Submerged Arc welding is best suited — can help the fabrication shop, shipbuilding yard and wind tower, rail car and pressure vessel production facility considering a conversion to the process.
The basics of SAW
Submerged Arc welding is a wire-fed process typically used with carbon steels, stainless steels and some nickel alloys, and it is best suited for materials that are 1/2-inch to 5-inches thick. It’s a common misconception that SAW is only for thick metals, however. It can be used to weld material as thin as 3/16-inch thick, by accounting for travel speed and heat input to avoid burn-through.
In SAW, a granular flux is used to protect the arc from the atmosphere; the Submerged Arc name refers to the fact that the arc itself is buried in the flux. The arc is not visible when parameters are correctly set and the layer of flux is sufficient.
The wire is fed through a torch that moves along the weld joint. The arc heat melts a portion of wire, flux and base material to form a molten weld pool. In this area, all important functions of the flux — degassing, deoxidizing and alloying — take place. Behind the arc, molten flux and metal freeze to form a slag-covered weld bead. When the welding process is correctly set, the slag should come off easily. Because of the necessity of the flux coverage, the SAW process is limited to the flat and horizontal positions.
The basic equipment necessary for Submerged Arc welding includes a power source; controller/interface; wire drive motor; torch; wire straightener; cables; and a flux hopper.
The reliability of power sources is essential in SAW, since they are often subjected to 100 percent duty cycles at high welding currents. Duty cycle refers to the number of minutes out of a 10-minute period a machine can operate, so having robust and durable equipment is important in SAW applications. A power source needs to be able to operate at welding currents as low as 350 amps for thin materials and more than 1,000 amps for thick materials.
Constant current (CC) and constant voltage (CV) can be used in the SAW process; CV equipment provides a consistent preset voltage, while CC equipment provides a consistent preset current. Technology is now available to easily switch between the two with a single machine. There are also process modes such as CV+C available, which offer additional benefits for SAW depending on the application.
Consider the consumables
Solid and metal-cored wire are used for SAW, and depending on the application, each should be considered to achieve the desired results.
The properties of metal-cored wires can offer increased travel speeds that result in even higher deposition rates with the same heat input. Cored wires also tend to have wider, shallower penetration profiles than solid wire, which helps to minimize the potential for burn-through on relatively thin materials or during root passes. In addition, cored wires can be filled with alloying elements to improve mechanical properties or offer additional solutions for high strength materials and high temperature applications.
The wire and flux combination should be matched to best meet application requirements, and they must be classified and qualified together. Special flux/wire combinations are available to meet specific requirements of demanding industries. Flux can vary in its composition, and certain types of flux offer different mechanical properties, such as higher impact values. Flux grain size also influences carrying capacity and flux feeding and recovery.
The welding parameters in SAW — arc voltage, welding current, travel speed, stickout, torch angle, wire diameter, wire feed speed and polarity — all influence the shape and quality of the weld and productivity, so it’s important to be aware of their individual and combined influence.
Higher deposition rates offer productivity gains
The much greater deposition rates that SAW offers is one of the biggest benefits of the process. Deposition rate refers to the amount of filler metal melted into the weld joint and is defined by pounds per hour.
Single wire SAW applications can achieve deposition rates of up to 40 pounds per hour, depending on wire size, type and polarity. Deposition rates with SubArc welding often can be increased even more when using a tandem torch option or pairing the process with metal-cored wire.
Submerged Arc welding is a highly productive process in even its simplest form — and most widely applied — method, which is single wire welding. But there are a variety of other process options and torch configurations available that can further increase welding productivity and help optimize results. Those include twin wire, tandem wire and multiwire SAW.
Systems with multiple wires feeding in the same puddle — called tandem SubArc welding — can achieve deposition rates of more than 100 pounds per hour with three or more torches.
These high deposition rates can offer great benefits in productivity and increased throughput.
SAW also can offer deep penetration, which is important for thicker base materials. The more heat that is put into the weld, the more penetration that can be achieved. The penetration depth is tied to the amount of current that is used for welding.
Quality and comfort benefits
Because Submerged Arc welding is a consistent, often highly automated process, it can offer excellent weld quality and consistent, repeatable results, with minimal spatter and weld fume.
Those characteristics also offer benefits for operator comfort and a worker-friendly environment. With SAW, the welding operator is not bent over the workpiece welding during the process, which improves comfort and ergonomics.
Also, the low fume and lack of open arc with SAW can contribute to greater operator comfort and safety, especially when the application involves long periods of welding.
Return on investment
In many operations that use Submerged Arc welding, the welding equipment is a small part of the total fabrication system or process. The SAW equipment is often integrated into additional automation equipment — such as manipulators, positioners, gantries or custom systems — to help achieve the most efficient results.
So while converting to SAW can mean a larger upfront investment, the major productivity capabilities the process provides result in a fast return on investment.
An operation or shop that switches to SAW can double or even triple productivity and make more efficient use of labor time, outcomes that help justify the initial investment.
Updated SAW offerings from Miller
Updates to SAW offerings from Miller have resulted in the new Digital SubArc Series of machines that are easy to setup and operate, for a superior arc in demanding industrial applications.
The addition of digital control communication technology to the machines allows for more remote capabilities and an intuitive user interface, for simplified integration of the equipment in more advanced applications.
The interface provides the operator with the ability to set process parameters and control output easily, with easy setup and operation. The SAW Digital Series interface controls recognize what power source and wire drive are connected — information that previously had to be inputted manually — and automatically configure the system for proper operation.
The Miller Digital SubArc Series also offers simplified setup with the tandem cable, which provides the benefit of automatic phase shifting once the cable is connected.
Paralleling of equipment also has been simplified with the updated Miller SubArc Digital Series. Paralleling is used in applications that need more than 1,000 amps. Hooking a parallel cable to the front of two 1,000 amp machines results in 2,000 amps. With the updated SubArc Digital Series, no special tools or software are needed to do this; paralleling can be achieved by simply connecting the cable between the two units, and the system automatically shares the load between the machines and updates the interface.
In addition to the Miller Digital SubArc Series, a complete line of Hobart consumables is manufactured for high performance and provides many options for a variety of applications. Hobart offers solid wire, both carbon and low-alloy steels, as well as a variety of nickel-based and stainless steel alloy wire. Hobart also offers stainless steel strip and some nickel alloy strips for SubArc Welding and Electroslag Welding Strip cladding applications. There are also a variety of flux offerings that best match the specific industry and application — from a low to high basicity level to achieve different levels of mechanical properties.
Realize productivity benefits
Process improvements can be profit-boosting initiatives for companies. The numerous advantages Submerged Arc welding offers for productivity and weld quality make an investment in the process one to consider, especially in heavy industrial applications.
Understanding the SubArc welding process and the overall equipment needs — and selecting the proper wire and flux combination for the application — can help an operation realize the full potential of the process.