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.
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What do you do when you need to repair a worn surface on an item such as a nozzle, ball valve, roll tool, or a shaft? In such cases, cladding might be the way to go. It is usually more cost-effective to apply the specialty layer only where needed rather than fabricate the entire structure from the more expensive alloy. Cladding can be done in a number of ways, but one of the most flexible is weld cladding.
All welding processes can be used for cladding, but constraints in the physical requirements make some welding processes better suited to the process than others. For example, gas tungsten arc welding GTAW is not well-suited to cladding large items or areas that need a large amount of buildup.
On the other hand, GTAW can be an excellent candidate when cladding in restricted areas, such as on the ID of a small-diameter valve. Strip cladding processes are well-suited for applications that require high deposition rates. They have been used for decades.
One of the most commonly used processes, submerged arc strip cladding SASC , also is one of the most productive, offering deposition rates of about 33 lbs. However, technologies change, and advancements in consumables have made electroslag strip cladding ESSC a good alternative to SASC in some applications, such as oil and gas, pressure vessel, and petrochemical.
ESSC can save time and material costs and increase the deposition rate. The arc in SASC runs along the entire strip width. Because the weld pool penetrates the base material, dilution levels typically are about 20 percent. ESSC uses a delivery system to feed the strip, much like wire is fed through a gun in a typical wire welding process.
Because ESSC is not an arc process, heating takes place in the flux, which is conductive. The heat melts the strip and base material into the liquid slag, which then is 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 see Figure 1. The heat input of the two processes is comparable. Because the dilution rate with ESSC is low, the process often can be completed by applying just one layer of material at a standard travel speed, whereas two layers typically are required when using a high-speed ESSC flux.
This reduces the consumable cost by half. ESSC has a high deposition rate, in some cases reaching 55 lbs. Another time-saving benefit of 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 postweld cleaning is necessary for some applications. Figure 1a Electroslag strip cladding ESSC can take one of two forms: a single hopper of flux to cover the leading edge of the weld a or two hoppers to cover both the leading and trailing edge b.
Cladding is typically a 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 reduced use of welding consumables mean the return on investment can be a few months.
Figure 1b Electroslag strip cladding ESSC can take one of two forms: a single hopper of flux to cover the leading edge of the weld a or two hoppers to cover both the leading and trailing edge b.
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ESW - Electroslag strip cladding
Electroslag Strip Cladding Offers Productivity and Cost Benefits
Electroslag cladding provides alternative to standard cladding techniques