The process is often used when there is a need to use mild or low-alloy steel for the main structure with a specially alloyed material applied to a certain portion of the work piece to accommodate necessary properties. It is more cost effective to apply the layer only where needed, rather than fabricating the entire structure from the more expensive specially alloyed material. Cladding offers a solution in these situations.
There are many types of Cladding, but one of the most flexible is Weld Cladding. All welding processes can be used for Cladding, but due to constraints in the physical requirements, some welding processes are better suited for Cladding than others. For example, TIG Cladding lacks the necessary deposition rate — it’s about 5 pounds per hour — to be used with larger, thicker materials, but it is ideal for small inside diameters or restricted areas.
Strip Cladding processes are better suited for applications where a high deposition rate is desirable and where the part will accommodate this higher rate of deposition. Strip Cladding has been around for decades, and historically, Submerged Arc Strip Cladding (SASC) has been the most commonly used process, offering deposition rates of about 33 pounds per hour.
However, technology advancements, especially related to consumables, have made the Electroslag Strip Cladding (ESSC) process a good alternative in some applications, such as oil and gas, pressure vessel and petrochemical — one that can save labor time and material costs and greatly increase the deposition rate. SASC and ESSC are the formal designations, but the processes are also commonly referred to as SAW and ESW.
How Strip Cladding works
Electroslag Strip Cladding and Submerged Arc Strip Cladding are similar processes, but they differ in that SASC uses an arc, while ESSC is a resistance heating process that does not use an arc.
With Submerged Arc Strip Cladding, an arc runs along the width of the strip, depositing weld metal on the base material. Because there is penetration into the base material, dilution levels typically are about 20 percent with this method.
With Electroslag Strip Cladding, the strip is fed through a delivery system much like wire is fed during a typical wire welding process. Since ESSC is not an arc process, heating takes place in the conductive flux, and the resulting heating effect melts the strip and base material into the liquid slag, which is then transferred into molten metal that is deposited onto the base material. The strip actually rides on top of the slag system created by the flux, protecting the weld.
Another difference between Submerged Arc Strip Cladding and Electroslag Strip Cladding is that the flux is delivered in front of the weld in ESSC, while in SASC, the flux is delivered at both the front and behind the weld, to shield the arc from atmospheric contamination. The flux for each process looks similar, but the ESSC flux is specifically formulated to work with that process.
Electroslag Strip Cladding offers some advantages when compared to its SASC counterpart, including a reduced dilution rate of base material into the weld — typically about 10 percent for ESSC compared to 20 percent for SASC — along with greater deposition rates, improved travel speeds and lower flux consumption. The heat input of the two processes are comparable.
Deposition rates of 55 pounds per hour
Because the dilution rate with ESSC is much less, the process can often be completed by applying one layer of material using a flux for standard travel speed — whereas two layers are typically required when using a high-speed ESSC flux. That compares to the minimum of two passes needed to get the required overlay chemistry with Submerged Arc Strip Cladding.
The need to deposit only one or two layers of material by using ESSC not only saves labor time and costs, but it also reduces the necessary strip material needed for the application, resulting in consumable savings.
The typical travel speed offered by the ESSC process is double that of Submerged Arc Strip Cladding — 10 inches or more per minute compared to 5 inches per minute. This is achieved mostly due to the higher deposition rate that is realized while still maintaining a similar layer thickness, so more metal is being deposited in the same amount of time.
Electroslag Strip Cladding also offers greater deposition rates — about 55 pounds per hour, compared to the 33 pounds per hour typically offered with Submerged Arc Strip Cladding. A higher deposition rate, combined with increased travel speed, reduces welding time and improves productivity for manufacturing and fabrication applications.
Another time-saving benefit offered by the ESSC process stems from the electroslag refining that occurs when the molten metal passes through the slag bath. This results in cleaner weld metal with lower oxygen levels, which means less post-weld cleaning is necessary for some applications.
Best practices for optimized results
To obtain the desired weld metal composition, it’s important to choose the right combination of strip electrode and flux together with correct welding parameters.
For Electroslag Strip Cladding, it’s necessary to use a dedicated ESSC flux that provides good electrical conductivity at high temperatures. This is typically done with a higher content of fluorides in the flux.
The optimal voltage for the ESSC process is governed by the flux, and it tends to be a narrower voltage window compared to SASC. It’s important to note that too high a voltage will cause spatter and unstable fusion, but too low a voltage increases the risk of short-circuiting as a result of the strip sticking to the base metal.
In consumable selection for ESSC, the strip width needed for the application is determined by the size and shape of the components to be surfaced. The strip electrodes are typically .5 mm thick, and standard widths include 30, 60 and 90 mm.
With Electroslag Strip Cladding, it’s important to use magnetic steering when the strip width is greater than 60 mm. Due to the magnetic field created by the high current, the molten metal moves from the edge to the inside of the cladded plate. Using magnetic steering connected to the welding head can help control this effect.
Choosing equipment, accessories and consumables designed for Electroslag Strip Cladding can help manufacturers find success with the ESSC process.
Consider return on investment
The Electroslag Strip Cladding process may require investing in more equipment than SASC, a factor that may make some companies hesitant to consider the process. Cladding is typically a very continuous operation that requires high amperages and high duty cycles.
However, the productivity and efficiency gains that result from the increased travel speeds and deposition rates, lower dilution rates and the use of less welding consumables mean the return on investment can be only a matter of weeks for some operations.
It’s also important to be aware of which applications are best suited for the ESSC process, which can additionally enhance the benefits that are realized and help optimize the investment.
A viable option that offers productivity gains
Electroslag Strip Cladding can double the travel speed, greatly increase deposition rates and reduce dilution rates for manufacturers and fabricators using an automated process.
In combination with lowered usage of welding flux and strip, these productivity and efficiency benefits of Electroslag Strip Cladding can help companies save time and money, allowing them to be more competitive and profitable.