How to choose the right wire and flux for SAW

The submerged arc welding (SAW) process can offer excellent productivity, providing you with a potential competitive edge. However, the wide range of wire and flux combinations on the market can make selecting the best products seem intimidating. Often it&#;s not a simple &#;if X is the case, then use Y filler metal&#; answer. There are several factors to consider.

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It&#;s important to understand how the wire and flux will interact with each other and the weldment. That choice ultimately will require some compromise. Discovering as much as possible about the application&#;s requirements helps identify potentially costly and time-consuming conflicts between expectations and reality during the selection process, as opposed to during implementation.

Most important, answering the following key questions provides insight into the big question: Which wire and flux is best for me?

Question 1: What Are the Design and Fabrication Requirements?

Codes and specifications are best practices compiled by those experienced in the industry to guide filler metal selection. Understanding the application code requirements is key for both compliance and performance. These often identify the exact wire and flux classifications that must, can, or cannot be used.

For example, a common structural fabrication code is American Welding Society (AWS) D1.1. It requires the use of specific wire and flux classifications (shown in an expansive table) for prequalification of welding procedures, depending on the base material being used. As another example, AWS D1.5, a common bridge fabrication document, limits use of active fluxes to one- and two-pass welds.

However, these and most other documents still allow some level of flexibility in filler metal and flux that you can use. Most also provide requirements for using a new wire and flux combination with existing procedures without requalification. While requalification can cost time and money, it may be worth the effort to optimize the SAW process with the best combination for the application, and make it more productive.

Some agencies, such as the American Bureau of Shipping (ABS) and Det Norske Veritas (DNV), require type approval/classification of the wire/flux combination before you can use them. Consult the filler metal manufacturer for a listing of their approved wire and flux combinations and with an agency auditor to ensure the application is supported by the classification of products.

Question 2: How Will the Part Be Used?

Achieving the appropriate mechanical and chemical properties in the SAW process depends on both the wire and flux. A common approach is to select a wire and flux that produce a weld that closely matches the strength and toughness of the base material. However, there are exceptions and additional considerations based on how you&#;ll use the part, for example, parts subject to static, dynamic, and impact loading.

Static loading, in which load does not change, has the least stringent requirements, providing the most flexibility in choice.

Dynamically or cyclically loaded weldments undergo fluctuations in load during service&#;sometimes quite frequently. These loading conditions require a wire/flux combination that results in a more ductile weld. Excessive tensile strength reduces ductility; therefore, active fluxes or wires with high alloy contents can be problematic in these applications. Unlike neutral fluxes, active fluxes contribute significantly to the manganese and silicon composition of the weld and, as a result, its strength. When possible, choose a wire/flux combination that provides a tensile strength closer to the minimum allowable (with a factor of safety, of course) because it can help improve ductility.

Impact loading, in which high loads are applied quickly, requires a wire/flux combination with higher toughness. To achieve this toughness, consider using a wire with a medium to high manganese level as manufactured, such as an AWS EM12K or EH12K. Another option is one containing nickel. Combine one of these wires with high-basicity flux to achieve optimal toughness levels.

Question 3: Where Will the Part Be Used?

The service conditions the weld will encounter, such as high or low temperatures and/or corrosion, affect which wire and flux you choose. Again, a common approach is to select a wire and flux that produce a weld that closely matches the base material&#;s chemical composition.

High service temperatures, like those found in boilers and power generation applications, require special alloys such as chrome-moly. Chrome-moly alloys, in turn, require wires and fluxes with low residual content, or X-factor, to help prevent cracking from temper embrittlement. Low service temperatures also require special alloys; wires that contain nickel are good to provide toughness in these circumstances, and high-basicity fluxes should also be considered. Special low-ferrite versions of common austenitic alloys are available when service requirements involve cryogenic temperatures.

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Parts exposed to sources of corrosion also affect filler metal selection since various alloys react differently to these mediums. This holds true for stainless steels, which are used in many different corrosive environments. For these applications, it is helpful to note the corrosive medium and required component lifespan, and then consult a filler metal manufacturer for recommendations.

Question 4: Will It Be Heat-Treated?

Like base metals, filler metals can undergo significant changes when heat-treated. Some SAW wires are designed to maintain good mechanical properties following extended postweld heat treatment, while others are less resilient.

The AWS classification for SAW wires uses a designator to provide insight on the best options for heat-treated applications. However, be aware the classification typically indicates the mechanical properties at one hour of heat treatment. A filler metal manufacturer can provide information for additional time and temperatures.

Question 5: What Are the Productivity Requirements?

Choosing the right wire and flux for the application can improve productivity by increasing deposition rates and travel speeds, as well as reducing time spent on cleanup and rework. Consider these factors:

• Metal-cored versus solid wires. The tubular design of metal-cored wires provides higher deposition rates and faster travel speeds in SAW applications compared to solid wire welded at the same current. Metal-cored wires are available in both carbon and low-alloy steel options. Metal-cored wires also offer a wider, shallower penetration profile. Using these wires can help fight burn-through for reduced rework and better productivity.
• Current-carrying capacity. Flux formulation influences the flux&#;s current-carrying capacity&#;the maximum current (and therefore the greatest deposition rates) at which high-quality weld profiles can still be obtained. Certain fluxes are designed for multitorch SAW setups, welding at high currents or at high travel speeds. Check with the manufacturer to ensure the flux does not have a lower current-carrying capacity than your application requires.
• Polarity. Employing a modern variable-balance square-wave alternating current (AC) power source allows for adjustments between high penetration and high deposition rate without necessarily changing amperage. Fluxes can be designed for use in direct current (DC) only or for use with both DC and AC. The AC designator in the flux&#;s EN ISO classification indicates use for both AC and DC, while a DC designator indicates only DC should be used.
• Heat input. Higher amperage means a higher wire feed speed, which equals better deposition rates and throughput. High amperage also translates to high heat input in the weld, which affects mechanical properties. The alloy content of some wires makes them suited to high-heat welding by helping maintain acceptable properties. In addition, certain flux combinations are better suited for high-heat welding. Low-basicity fluxes tend to improve overall operating characteristics, especially when using high-productivity (hot and fast) parameters. High-basicity fluxes tend to offer improved toughness than lower-basicity fluxes under most conditions, but may not at high heat inputs.
• Pre- and postweld cleaning. Active fluxes contribute significant silicon and manganese, which are deoxidizers that help clean the material during welding to cut down on rework time. Welds made with active fluxes, as well as low-basicity neutral fluxes, typically wet out smoothest and have the best slag release when welding at higher travel speeds or when the base material is rusty, scaly, or dirty. This reduces the risk of poor weld quality and time spent on pre- and postweld cleaning. Wires with high manganese and silicon (deoxidizers) can also help prevent porosity.

Question 6: How Will the Part Be Welded?

Joint design and the manner in which the part will be welded are important factors when it comes to choosing the appropriate wire and flux.

The deep, narrow penetration profile of solid wire, for instance, makes it suitable for narrow and square groove welding, while the higher deposition rate and wider profile of metal-cored wires are advantageous for wider grooves and fillet welds. In addition, certain fluxes are specially designed to assist with slag release in narrow groove welding. A flux that releases best in a wide groove may not do so in a narrow groove, and vice versa.

Neutral fluxes are suited for large, multipass weldments because they help maintain consistent and acceptable mechanical properties. Active fluxes typically should be used only for single or two-pass welding, as the excessive alloying that occurs in large multipass welds can contribute to brittle, crack-sensitive welds.

Also consider if the application is plate or tubular welding. Fluxes specially designed for pipe welding may offer a slightly higher freezing rate, which helps prevent the puddle from spilling.

Look Beyond Cost

When selecting SAW wire and flux combinations, the best option isn&#;t necessarily the least expensive. Mild steel metal-cored wires may cost more than similar solid wires, for example, but they can help improve productivity and efficiency. The greatest leap in welding productivity can be realized using multiwire configurations such as twin or tandem wire, although some level of capital investment is required. But small increases in consumable or equipment cost can quickly provide significant reduction of labor cost.

Submerged arc welding or SAW is a commonly used welding process for thick steel sheets or long welds. There are four components to this process. The welding head is used to feed flux and filler metal to the area that is being worked on. With the help of the electrode, the filler metal gets energized too. The flux hopper stores and controls the flux.

The 4 Components of SAW

The granulated flux is an extremely important part. It allows the metal to be cleaned and shields molten atmospheric contamination. The granulated flux can be fused, mixed or bonded materials. It is also mixed with different materials depending on what the project is. The electrode or filler metal is usually in the form of a wire. There are special forms as well. If a wire of filler metal is twisted it will give the arc an oscillating movement. The types of material that can be added with the electrode is used for are nickel-based alloys, low alloy steel, carbon steel, and stainless steel. Other options that can change jobs up are the wire feed speed, travel speed, arc voltage, current type, electrode stick-out, and contact tip.

This type of arc welding starts with the flux feeding the filler metal onto the joint. Placing steel wool between the electrode and joint before starting, works just as well as lighting the electrode with a torch to start. Once molten, the flux goes from being an insulator to a conductor. The wasted flux material or slag is removed after the weld. The electrode has several speeds. Predetermined speed is a continuous feeder. Semi-automatic speed allows manual movement of the head. Automatic speed is good for stationary jobs. The arc can be shortened and lengthened manually.

The Pros of Submerged Arc Welding

There are some pros and cons to all types of welding. The submerged arc welding process is a specific type of weld. To start, the job will have higher deposition and high operating factors with mechanized jobs. Sound and deep penetration welds are made possible with easy control. Thicker sheets of metal are typically used for these welds, but thin sheets can be done. Another pro is the lack of edge preparation needed and little fumes created. The work can be done outside or inside and the welds are uniform and corrosion-resistant. Even with a thick sheet, a single pass is possible. Finally, the arc is always covered to allow no chance of splatter. One great thing is that more than half of the flux can be reused.

The Cons of Submerged Arc Welding

When it comes to arc welding, there are a few specific cons. This is due to the fact that it is a very specific weld type. The first obvious con is that the only materials to work on are some types of steel and some nickel-based alloys. The equipment can only be in the position of 1F, 1G, and 2F. It is also limited to rotating pipes, vessels or straight seams for welds. The flux can be a bit troublesome to set up and can cause health concerns. A huge con is a fact that only thick welds are workable. There are also requirements for slag removal before you start and backing strips for root penetration.

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