1.5 SAW — Submerged Arc Welding

Submerged Arc Welding (SAW)

Submerged Arc Welding (SAW) is the high-production, mechanized process in which the arc burns entirely beneath a blanket of granular flux — hence "submerged." Because the flux hides the arc, there is no visible arc, no spatter, and no ultraviolet radiation, and the process posts the highest deposition rate of any single-arc process, 25–100+ lbs/hr. It is the backbone of plate girders, pressure-vessel shells, pipe seams, and wind-tower fabrication.

A bare solid or metal-cored wire is fed continuously into the joint while a hopper lays granular flux ahead of and around it. The arc melts wire, base metal, and part of the flux into a pool; the molten flux becomes a glassy slag and the unmelted flux is vacuumed up and recycled. Most SAW runs on constant voltage (CV) for smaller wires (self-regulating, like GMAW), while large-diameter wire often uses constant current (CC) with voltage-sensing feed.

A practical consequence of burying the arc is that operator fume and arc-flash exposure are very low, but it also means the weld must be set up so precisely on the joint line that even a small mistracking can run the bead off the seam unseen.

SAW is highly adaptable to multi-electrode arrangements that push deposition even higher. Tandem SAW runs two or more wires in line — typically the lead wire on DC for penetration and a trail wire on AC for fill and bead shape — and twin/parallel setups feed two wires through one contact tip. Cold-wire and hot-wire additions and iron-powder fill can further raise deposition without adding arc energy. The inspector should appreciate that these productivity boosts also raise total heat input and the risk of inter-run slag entrapment, so parameter control and inter-pass cleaning are scrutinized.

Because SAW is mechanized, the operator's role shifts from manual bead control to setup, parameter monitoring, and joint tracking, which is why operator-qualification and machine-calibration records become central to the inspector's documentation review.

Operating Parameters

Consumables, Flux Types, and Limits

SAW wire/flux are classified together under AWS A5.17 (carbon steel). The wire EL12 means Electrode, L low manganese, 12 = ~0.12% carbon. The flux-wire combination is what gets certified for mechanical properties.

Flux-wire example: F7A2-EL12

Positions and Inspection

SAW's defining limitation: it is flat (1G/1F) and horizontal (2F) only, because the loose granular flux must rest on the joint by gravity — it cannot be made to stay on a vertical or overhead surface. It also suits only long, straight, or circular (rotated) seams, and on circumferential pipe seams the workpiece is rotated under a fixed head so the weld stays at top dead center. Thick SAW joints are frequently welded from both sides, which makes back-gouging of the first side (usually by CAC-A) before the second pass a routine step the CWI verifies for complete joint penetration.

Because the arc is hidden, the operator cannot watch the puddle, so mechanical tracking, controlled parameters, and downstream NDE carry the quality burden. Inspectors watch for slag inclusions between SAW passes (multi-wire/tandem setups are common), lack of fusion at high travel speeds, and hydrogen cracking if bonded/agglomerated flux has picked up moisture — which is why such flux is held in heated hoppers. 6 kJ/in)**, often demanding control of cooling rate and grain growth in the HAZ.

Exam trap: SAW is flat and horizontal only (gravity holds the flux). It has the highest single-arc deposition rate but cannot weld vertical or overhead.

A5.17 Flux-Wire Classification and Flux Manufacture

The flux is half of the SAW consumable system, and how it is made governs both what it can do metallurgically and how it must be handled. The three manufacturing routes give very different behavior:

Because bonded and agglomerated fluxes can carry deoxidizers and alloying additions, they let a fabricator tune weld-metal chemistry — but they also absorb moisture, which is a direct hydrogen-cracking risk, so they are stored sealed and run from heated hoppers. Fused flux trades that flexibility for stability.

Decoding F7A2-EL12

The full SAW flux-wire designation pairs a flux property string with the electrode. F7A2-EL12 reads as: F = flux; 7 = 70 ksi minimum tensile (and a defined yield/elongation set); A = tested in the as-welded condition (a P here would mean tested after PWHT); 2 = Charpy V-notch of at least 20 ft-lb at −20°F; EL12 = a low-manganese (L) solid electrode of about 0.12% carbon. The same flux can earn different ratings with different wires, which is why the flux-wire combination, not the wire alone, is what gets certified for mechanical properties.

Multi-Wire and Tandem Productivity

SAW scales deposition far beyond a single arc. Tandem SAW runs the lead wire on DC for penetration and a trailing wire on AC for fill and bead shape; twin/parallel setups feed two wires through one tip; cold- and hot-wire additions and iron-powder fill raise deposition without raising arc energy. These arrangements drive deposition into the 25–100+ lb/hr range and let single-pass penetration reach roughly 1 inch, but they also raise total heat input and the chance of inter-run slag entrapment, so the inspector scrutinizes parameter control and interpass cleaning.

The Flat/Horizontal Limitation

SAW's defining restriction follows directly from physics: the loose granular flux is held in the joint only by gravity, so the process is limited to flat (1G/1F) and, with care, horizontal (2F) positions and cannot be made to weld vertical or overhead. It therefore suits long straight seams and circular seams welded with the work rotated under a fixed head so the puddle stays at top dead center.