Submerged Arc Welding (SAW) is a common arc welding process that is typically operated in the automatic or mechanized mode. Also known as Sub-Arc, this process uses a bed of powdered flux on top of the area being welded to prevent contamination from the atmosphere, and is normally used on pipes and pressure vessels with thicker walls (more than ½” in thickness). Sub-Arc welding systems are typically installed on X-Y Manipulators and are only used for fill and cap passes.
The Spool Welding Robot (SWR) uses modified short circuit waveforms such as RMD, LSC and STT for root pass and the GMAW-P weld process for fill and cap passes. GMAW welding is a process that uses inert gas rather than flux to cover the area being welded. This welding process uses shielding gas such as CO2 / Argon blends to protect the process from contaminants in the air and to keep atmospheric nitrogen /oxygen away from the molten metals.
SWR or Sub-Arc manipulators
While the Sub-Arc welding process is much more efficient than the GMAW process due to higher deposition rates, all production factors have to be considered in the decision to purchase the right mechanized manipulator.
Root and hot pass welding and material handling time
Typically when welding pipes or vessels with Sub-Arc systems the root pass is done manually at a different welding station and then the pipe or spool has to be moved to the Sub-Arc welding station for fill and cap passes. Also a hot pass is required over root prior to SAW pass. In comparison the SWR uses the GMAW from root to cap in a single welding station which results in a much more efficient process on pipes or vessels less than 0.75 inch compared to Sub-Arc manipulators. As a result, the faster deposition times of Sub-Arc process will be washed away with the extra root and hot pass welding and extra material handling time for thicknesses of less than 0.75inch.
Flux handling system
SAW process requires a flux handling system but the SWR does not require such a system, nor a post-weld slag removal, and it is able to consistently create high quality welds with eliminating the possibility of slag entrapment defects. The complexity and cost of the flux handling/recovery systems have to be considered in the total cost of ownership.
Project mix
Sub-Arc manipulators further require longer setup times which only make economical sense for large projects that can justify the setup of Sub-Arc manipulators. In contrast, the SWR can weld pipes of less than 0.75 inch and be used for smaller or infrequent projects of welding pipes or vessels with larger than 0.75 inch thickness. Having a pipe welding machine that can be used in both scenarios is a huge advantage for production managers that need to deal with a high mix of projects in their operations. The SWR’s user friendly HMI and ease of positioning from joint-to-joint clocks the industry’s fastest setup time while covering the largest spool variety (spools upto 30ft long, 2inch to 60inch diameters, slip-on flanges, etc).
To summarize, purchasing Sub-Arc manipulators are only justified when steady stream of projects requiring welding of thick pipe or vessels (greater than 0.75inch) can be guaranteed.
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