Flux-Cored Arc Welding uses a continuously fed tubular wire whose core carries flux and alloying elements. It is the high-deposition cousin of MIG, built for thick steel, heavy fabrication, and outdoor work.
FCAW wires are classified under AWS A5.20 (carbon steel) and A5.36. Gas-shielded wires like E71T-1 need an external shield — 100% CO₂ or 75/25 argon/CO₂ — and deliver smooth, high-deposition welds with light slag; the suffix "-1C" means CO₂, "-1M" means mixed gas. Self-shielded wires such as E71T-11 and E71T-8 carry all of their shielding in the core, so they weld in wind with no gas bottle — E71T-8 is the workhorse for bridge and structural work because of its low-temperature impact toughness.
The flux core forms a slag that supports the bead in all positions and protects the solidifying metal, but it must be chipped between passes. Deposition runs roughly 8–15 lb/hr with a single wire — double typical MIG — so heat input and duty cycle, not feed rate, are the real limits. Stick-out differs by family: gas-shielded wires run about 3/4", self-shielded up to 1-1/4" — too much stick-out starves the weld of shielding and causes porosity.
| Wire | Polarity | Shielding | Volts | Wire Feed (IPM) | Amps | Gas (CFH) |
|---|---|---|---|---|---|---|
| 0.035" E71T-1M | DCEP | 75/25 Ar/CO₂ | 22–26 V | 200–280 | 130–190 A | 35–40 |
| 0.045" E71T-1C | DCEP | 100% CO₂ | 24–28 V | 220–320 | 200–300 A | 35–45 |
| 0.045" E71T-11 | DCEN | Self-shielded | 17–19 V | 200–300 | 150–250 A | None |
| 1/16" E71T-1C | DCEP | 100% CO₂ | 26–30 V | 180–260 | 300–400 A | 40–50 |
| 1/16" E71T-8 | DCEN | Self-shielded | 18–22 V | 140–200 | 250–350 A | None |
Self-shielded wires need a long stick-out (3/4–1-1/4") and must never be run with external gas. Drag the gun 15–25° for both families.
A constant-voltage power source drives the arc while the wire feeder pushes a tubular wire through the gun. The flux in the wire core does double duty: it generates shielding gas, and it forms a slag that protects the weld as it cools.
Constant-voltage power source holds the voltage steady; wire feed speed — not voltage — controls the current and deposition rate.
Wire feeder pushes the tubular wire through the liner at a set IPM, through knurled drive rolls matched to the wire.
Contact tip transfers welding current to the wire, which extends beyond the nozzle as stick-out.
Arc formation — the wire touches the work, shorts, and strikes an arc that melts the wire and base metal into a pool.
Flux creates shielding gas — core compounds burn and decompose to shield the arc; self-shielded wires add deoxidizers for wind tolerance.
Slag formation — lighter molten flux floats on the weld pool, sealing it from air as it travels behind the arc.
Weld pool solidification — the metal freezes under the slag blanket, which supports the bead out of position and slows cooling.
Slag removal — the cooled slag is chipped and brushed off between passes so it cannot become a trapped inclusion.
FCAW shares a rig with MIG, but the drive rolls, contact tips, and gun consumables must be matched to tubular wire. Here is everything needed for a gas-shielded setup.
Constant-voltage DC machine rated for the amperage and duty cycle you need — 250 A for most shop work, 450 A+ for heavy wire.
Smooth, constant-speed feed. Set the drive-roll pressure light enough to avoid crushing the tubular wire.
Air-cooled for light work, water-cooled for high amperage and 1/16" wire. Match the liner to wire type and diameter.
A poor ground arc-seeks through tables and bearings. Use a clean, tight clamp on bare steel near the joint.
Only for gas-shielded wires: CO₂ or 75/25 Ar/CO₂, with a flowmeter set to 35–50 CFH. Self-shielded runs no gas.
Work lead and whip sized for the machine's output; oversize for long runs to prevent voltage drop at the arc.
Knurled V-groove or U-groove rolls sized to the wire — solid-wire rolls crush tubular wire and cause erratic feed.
One size per wire diameter. Replace worn tips (oversized bore causes erratic arc) and keep the nozzle free of spatter.
E71T-1C/-1M, E71T-8, E71T-11 or E70C-6M depending on shielding, position, and service. See the consumables section below.
Chipping hammer, wire brush, anti-spatter spray, and tip cleaner — slag control is half the job with FCAW.
Auto-darkening helmet with UV protection, welding gloves, long-sleeve jacket, and approved footwear. FCAW throws more fume and spatter than MIG.
The wire class decides everything: shielding, position rating, toughness, and what gas — if any — the joint needs. Small diameters handle out-of-position work; large diameters maximize flat-position deposition.
| Class | Shielding | Positions | Best For |
|---|---|---|---|
| E71T-1 | Gas | All | Shop production |
| E71T-8 | Self | All | Bridge / structural |
| E71T-11 | Self | All | Field / light structural |
| E70C-6M | Gas | All | Metal-cored, no slag |
Suffix "-1C" = CO₂ shielding, "-1M" = mixed argon/CO₂ gas.
Typical flow: 35–50 CFH. Wind over ~5 mph breaks gas coverage.
Tip bore must match wire size exactly — oversize bores give an erratic, wandering arc and burnback. Nozzles collect spatter quickly; coat with anti-spatter compound and clean every few passes. Keep a spare tip and nozzle on the bench.
Anti-spatter spray or gel on the nozzle and work surface keeps spatter from sticking. The chipping hammer breaks slag, the wire brush removes it — both between passes, every pass, or inclusions will be trapped in the weld.
Flux-cored wire is hygroscopic — it absorbs moisture that becomes hydrogen in the weld. Keep spools in their sealed bags, store them warm and dry, and return opened spools to the bag. Damp wire is the classic cause of worm tracks and cracking.
Both families run tubular wire, but they are different tools. Gas-shielded FCAW is a shop production process; self-shielded FCAW is the field welder's answer to wind.
| Feature | Gas-Shielded | Self-Shielded |
|---|---|---|
| Gas Required | Yes | No |
| Outdoor Use | Poor | Excellent |
| Wind Resistance | Low | High |
| Slag | Moderate | Heavy |
| Appearance | Better | Rougher |
| Deposition Rate | High | High |
| Typical Industry | Fabrication Shop | Construction |
Metal-cored wire (E70C-6M) is a third option: gas-shielded, nearly slag-free, and fastest of all — but flat-position oriented and not covered in detail here.
Position ratings are printed in the wire class — "1" means all positions, "2" means flat and horizontal only. The 0.045" and smaller wires carry the "1" rating; big 1/16"+ wires are flat-only machines.
Maximum deposition and speed. Any wire class works, including 1/16"+ heavy wires. The pool is supported by gravity — the slag runs behind the bead cleanly.
Most wires qualify. Keep the work angle slightly upward into the top member of a fillet and watch for slag lapping over the puddle, which buries inclusions.
Run only small wires (0.045" and under) with E71T-1 or E71T-8 approval. Use a slight weave or upward steps; the slag holds the pool in place as it freezes.
All-position wires only. Low heat, stringers, and a tight drag angle keep the puddle small so it doesn't sag. Watch for spatter raining down.
Approval by class: E71T-1, E71T-8, and E71T-11 are rated for all positions. E70C-6M and 1/16"+ versions of most classes are rated 2F/2G (flat + horizontal) only — check the AWS class before running vertical or overhead.
FCAW tolerates more mill scale than MIG, but the joint still decides the weld. Porosity, lack of fusion, and inclusions are almost always prepped into the part before the arc ever starts.
Mill scale is a poor conductor that destabilizes the arc and causes lack of fusion. Grind or brush to bright metal in the joint and 1" beyond each edge.
Rust carries moisture (hydrogen); paint burns into the puddle. Strip both from the weld zone. For galvanized steel, remove the zinc coating first — the fume is toxic.
Set per the WPS — typically 1/8" for a 3/8" plate groove with backing, tight for fillets. Too tight traps slag in the root; too wide burns through.
A 60° included angle is the standard for full-penetration grooves on plate. Narrower angles need more root opening; deeper grooves need more fill passes.
Members must align — mismatch over 1/16" makes the arc wander and the weld cross-section uneven. Check alignment at both ends and the middle before tacking.
Tack the joint at both ends and intermittently along long seams — enough tacks to stop movement, not so many they slow production. Chip the slag off tacks before welding over them.
FCAW is a drag process: the gun tilts back 15–25° and the arc works the leading edge of the puddle. Beyond that, six techniques cover nearly everything you will run.
Straight, no oscillation. Preferred for roots, overhead, and thin material — narrow heat zone, less slag trapping. Keep travel speed steady.
Oscillate the gun to lay wider fill passes — keep the weave to about 2–3× the wire diameter and pause briefly at each edge to fill the toes. Too wide buries slag.
Gun tilted 15–25° back from the travel direction. Required for self-shielded wire; best for gas-shielded too — better coverage, deeper penetration, clearer view of the puddle.
Small upward triangle or zigzag steps, pausing at the edges so each step freezes before the next. The slag ledge supports the pool. Small wire only.
Fast, thin, low-heat pass — only where the WPS allows it (mostly light sheet and specific pipe positions). Not a substitute for a qualified vertical-up weld.
Root, hot pass, fill passes, cap. Brush and chip every pass — nothing goes on top of slag. Watch interpass temperature; on thick plate it can dictate the whole weld.
The table above is a starting point. These are the controls behind every number — and what happens when you move them.
Gas-shielded: DCEP (electrode positive). Self-shielded: DCEN (electrode negative). Wrong polarity gives a violent arc, spatter, and shallow fusion — check it before anything else.
Contact tip to work distance: ~3/4" for gas-shielded, 3/4–1-1/4" for self-shielded. Too long starves the shielding and drops the arc heat; too short buries the tip in the puddle.
The puddle should run about 2× the wire diameter wide. Too fast → lack of fusion and a ropey bead; too slow → excess reinforcement and slag trapping under the puddle.
Work angle: ~0–15° on butts, 45° on fillets. Travel angle: drag 15–25°. The drag angle directs arc force into the joint and keeps slag behind the arc.
FCAW is a drag process. Pushing lets the arc blow slag over the leading edge of the puddle, burying inclusions. Self-shielded wire physically requires drag to hold its coverage.
Voltage sets arc length and bead shape; wire feed sets current and deposition. Raise voltage for a flatter, quieter bead; raise feed for more fill. Change one at a time and retest on scrap.
FCAW is the process behind most heavy steel that gets welded out of position and out of doors.
Columns, beams, and moment connections — gas-shielded E71T-1 in the shop, self-shielded E71T-8 in the field.
Hull plating, stiffeners, and deck structure — long vertical and overhead seams run continuously with 0.045" wire.
Qualified under ASME Section IX with certified wire classes; the slag-free metal-cored option speeds up shell seams.
Excavator buckets, frames, and wear plates — 1/16" wire at high deposition on thick, abused plate.
Fill and cap passes over a cellulosic root, run with self-shielded wire on the right-of-way in weather.
Abrasive-wear overlay and hard-facing repairs on crushers, chutes, and dragline buckets in remote locations.
E71T-8 self-shielded wire is specified for its low-temperature impact toughness and wind tolerance, per AWS D1.1.
Field repair of frames, pads, and structural members where portability and dirty material beat polish.
Ten defects cover nearly every FCAW rejection. For each: what it looks like, what caused it, and how to stop it.
Appearance
Gas bubbles — pin holes on the bead surface or cavities inside the weld, sometimes a spongy centerline.
Causes
Low gas flow, wind, dirty or wet base metal, wrong stick-out, damp wire, wrong polarity.
Prevention
Clean the joint, set 35–50 CFH and block drafts, hold spec stick-out, store wire dry, check polarity.
Appearance
Glass-like streaks or islands trapped inside the weld, often found by radiography or after grinding.
Causes
Slag left between passes, low voltage, weave too wide, pushing the gun instead of dragging.
Prevention
Chip and brush every pass, keep voltage up, limit weave width, drag the gun 15–25°.
Appearance
A visible gap where weld metal meets the base — the bead looks laid on top rather than melted in.
Causes
Too little heat, travel too fast, wrong gun angle, cold material, heavy mill scale.
Prevention
Raise wire feed and voltage, slow the travel, correct the angle, grind the joint, preheat when specified.
Appearance
A groove melted into the base metal along the weld toes, weakening the cross-section.
Causes
Voltage or amperage too high, travel too fast, bad work angle, weave too wide.
Prevention
Drop voltage slightly, fix the work angle, narrow the weave, slow down, cap the toe with a stringer.
Appearance
Holes or sagging drops blown through thin material — usually on the back side of the joint.
Causes
Too much heat, wire too large, travel too slow, excessive root gap.
Prevention
Smaller wire, lower feed, faster travel, or move to MIG short-circuit below 1/8" material.
Appearance
A tall, convex bead that rises well above the plate surface instead of blending smoothly.
Causes
Voltage too low, wire feed too high, travel too slow for the deposit.
Prevention
Raise voltage to flatten the bead, cut feed, or speed the travel — check the cap profile per the WPS.
Appearance
Wavy hairline cracks along the bead surface, visible under the slag — hydrogen damage.
Causes
Moisture in the flux, damp wire, contaminated base metal, long arc length.
Prevention
Store wire sealed and dry, clean the base metal, keep stick-out to spec, replace damaged spools.
Appearance
Longitudinal or transverse cracks in the weld or a star crack in the crater at the weld end.
Causes
Unfilled crater, hydrogen, high restraint, wrong wire class for the base metal, poor fit-up.
Prevention
Fill craters before stopping, use the right class (e.g. E71T-8 for low-temp service), control interpass, reduce restraint.
Appearance
Weld metal rolls over the base at the toes without fusing — a rounded lip that hides a cold joint.
Causes
Heat too low, excessive fill metal, wrong gun angle, puddle too big for the position.
Prevention
More heat and less fill, correct the angle, keep the arc on the leading toe until it melts in.
Appearance
Metal globules welded to the plate around the joint — cosmetic damage and extra cleanup.
Causes
Voltage too high or low, wrong polarity, worn tip, contaminated surface, wrong gas mix.
Prevention
Tune voltage, verify polarity, replace worn tips, clean the nozzle, use anti-spatter.
FCAW produces more fume than MIG and showers hot slag. Treat it accordingly: ventilate, shield, and cover everything before the trigger is pulled.
Welding fume is a known carcinogen. Flux cores add metal oxide fume on top of the usual mix — never weld without ventilation.
Stainless and hard-facing wires produce chrome VI — a serious carcinogen. Local exhaust plus respiratory protection are non-negotiable.
Work outdoors or use mechanical extraction rated for welding fume. Confined spaces need forced ventilation and a trained watchman.
Sparks and slag fly several meters. Clear flammables, cover openings, use hot-work protection, and watch for smoldering — even through wall gaps.
Auto-darkening helmet, leather or FR gloves, long sleeves, no pockets that catch slag. FCAW spatter sticks — cover skin.
Rated respirators (N95/P100 minimum, PAPR for heavy fume) when ventilation can't do the job — stainless, galvanized, and confined work.
The arc emits intense UV — arc eye and skin burn within seconds. Full shade-rated lenses and covered skin, always. Protect bystanders with screens.
Slag stays hot long after it leaves the joint. It bounces into pockets, boots, and collars — and starts fires. Brush it away from your feet and check for drips.
These five documents govern FCAW wire, procedure, and welder qualification. If you are quoting work or signing off welds, you will meet all of them.
| Standard | Scope | Why It Matters |
|---|---|---|
| AWS A5.20 | Carbon steel flux-cored electrodes | Classifies E71T-1, E71T-8, E71T-11 — chemistry, mechanicals, position ratings |
| AWS A5.36 | Consolidated carbon/alloy steel wire spec | Newer umbrella spec replacing A5.20/A5.29 for most new classes |
| AWS D1.1 | Structural steel welding code | Procedure qualification, acceptance criteria, and the low-temp rules for self-shielded wire |
| ASME Section IX | Welding & brazing qualifications | WPS/PQR and welder performance qualification for pressure vessels, boilers, and piping |
| ISO 17632 | Tubular cored electrodes for non-alloy steel | International classification and supply conditions equivalent to the AWS series |
The questions welders actually ask about FCAW — answered straight.
Flux-Cored Arc Welding is a semi-automatic process that feeds a tubular wire whose core carries flux and alloying powders. The core generates shielding gas and slag, giving high deposition rates, deep penetration, and outdoor capability on thick steel.
With matching wire classes the weld metal meets the same strength levels. FCAW wins on deposition rate, penetration, and outdoor work; MIG wins on thin material, cosmetic finish, and lower fume.
Yes. Gas-shielded stainless flux-cored wires — E308LT1, E309LT1, E316LT1 — make clean, high-quality stainless welds, usually with 75/25 argon/CO₂ shielding. Use fume extraction; chrome VI fume is a serious hazard.
Self-shielded wire (E71T-8, E71T-11) is built for it — the core carries its own shielding, so wind barely matters. Gas-shielded FCAW is wind-sensitive and needs screens or calm air.
The flux core burns to form slag that floats on the molten pool, protecting it from air while it solidifies — and it physically supports the bead out of position. It must be chipped and brushed off before the next pass.
Almost always one of: stick-out too long or short, wind or a draft pulling shielding away, low gas flow, dirty or wet base metal, damp wire, or wrong polarity. Check stick-out and flow first, then cleanliness.
Gas-shielded wire runs DCEP (electrode positive); self-shielded wire runs DCEN (electrode negative). Reverse it and you get a violent arc, heavy spatter, shallow penetration, and porosity.
For gas-shielded wires: 100% CO₂ for deep penetration at the lowest cost, or 75/25 argon/CO₂ for a smoother bead and less spatter. Self-shielded wires use no gas — adding it ruins the weld.
It's possible but not recommended casually. Zinc fume is toxic — remove the coating from the weld zone, use ventilation and a proper respirator, pick a wire matched to the base metal, and prequalify the procedure.
No — FCAW's high deposition and high heat burn through anything under about 1/8". For thin sheet, use MIG short-circuit transfer or TIG.
Volts × amps ÷ travel speed — the number that decides cracking on thick plate.
Set your CO₂ or argon/CO₂ mix and read the flow and bottle life you need.
Match wire class to base metal and service — from E71T-1 to E309LT1.
All-in-one machine settings helper for dialing in a starting point fast.
What wire and process fit 16 gauge vs 1-inch plate — before you strike the arc.
See drag angles, vertical up technique, and slag control in motion on the home page video library.
Watch the technique sections — drag angles, weaving, and vertical up — demonstrated on real steel.
Watch VideosA shop-floor cheat sheet with the parameter table, stick-out rules, and polarity quick reference.
Download from Library