C-P Systems
What Is Submerged Arc Welding (SAW)? | Process Engineering Glossary
What Is Submerged Arc Welding (SAW)?
In piping engineering and process engineering, submerged arc welding, or SAW, is an arc welding process in which a continuously fed wire electrode forms an arc beneath a blanket of granular flux. The flux covers the arc completely, so there is no visible arc flash, very little spatter, and almost no fume. As the flux melts, it forms a protective slag over the molten weld pool, shielding the metal from atmospheric contamination and shaping the finished bead.
How SAW Is Used in Pipe Fabrication
Because the arc is fully enclosed and the welding head is mechanized, SAW runs at much higher currents and travel speeds than manual processes. In process piping, it is used almost entirely in the fabrication shop, where the pipe turns on rotators beneath a fixed welding head so the joint stays in the flat position. A typical shop weld on large-bore carbon steel pipe combines a manual root pass with SAW fill and cap passes.
Applications
Large-Bore Pipe Fabrication
Fabrication shops use SAW for the fill and cap passes on circumferential butt weld joints in heavy-wall carbon and low-alloy steel pipe, where its deposition rate cuts the welding time on each joint.
Longitudinal Seam Welding
Pipe mills use SAW to weld the longitudinal and spiral seams of large-diameter welded metallic pipe. Material specifications often identify this product as DSAW, or double submerged arc welded, pipe.
Heavy-Wall Joint Preparation
On thick-walled pipe, SAW is often paired with a compound or narrow-groove pipe bevel that reduces the volume of filler metal needed to complete the joint.
Benefits
High Deposition Rates
SAW deposits weld metal several times faster than shielded metal arc welding, reducing the number of passes and the labor hours required for each joint.
Consistent Weld Quality
Mechanized travel and full flux coverage produce smooth, uniform beads with reliable fusion, which typically means lower repair rates when completed welds are examined by radiography or ultrasonic testing.
Better Working Conditions
With no visible arc and minimal fume, operators face less arc radiation and lower fume exposure than with open-arc processes.
Limitations
Limited to Flat and Horizontal Positions
Loose flux must rest on the joint to shield the arc, so SAW is not practical for fixed pipe in vertical or overhead positions.
Equipment and Setup Costs
Rotators, a welding head, and flux feed and recovery systems make SAW most cost-effective for repetitive work on larger pipe sizes.
Root Pass and Flux Control
Open-root pipe joints usually need a root pass made by another process, such as GTAW or SMAW, before SAW begins. Flux must also be stored dry, because absorbed moisture introduces hydrogen that can cause weld cracking.
FAQ
Can submerged arc welding be used in the field?
Rarely. Most field welding involves fixed pipe in vertical and overhead positions where flux cannot stay in place, so piping projects reserve SAW for shop fabrication.
How is a SAW procedure qualified?
The welding procedure and each welding operator must be qualified under ASME Section IX, which ASME B31.3 references for process piping. Operators complete a performance test similar to a welder qualification test, adapted for mechanized equipment.
How are SAW joints tracked during fabrication?
Each joint receives a number on the weld map, linking it to the welding procedure, the operator who made it, and its inspection results.
About C-P Systems
SETTING THE STANDARD FOR CHEMICAL ENGINEERING FIRMS EVERYWHERE
Through unmatched professionalism, knowledge and experience, we set the industry bar for chemical engineering firms. With decades of chemical plant engineering and piping design experience, our team of licensed engineers can handle any project scope.