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newSchoolWorks.com › VoTechWorks › Manufacturing & Marine › Shipbuilding / Marine Fabrication › Steel & Aluminum Welding for Marine Fabrication › Lesson 5
MFG-SHIP13-03 · Lesson 5 · 18 clock hours · lab

FCAW-G and FCAW-S on Shipbuilding Steel — Production Techniques

Objective. Students will set up and operate both gas-shielded (FCAW-G) and self-shielded (FCAW-S) flux-cored processes on carbon steel in flat, horizontal, and vertical-up positions, selecting wire classification and parameters from the WPS to produce welds meeting ABS workmanship standards.

FCAW-G and FCAW-S: How the Processes Differ

Flux-cored arc welding (FCAW) uses a continuously fed tubular wire electrode whose core contains flux ingredients that stabilize the arc, shield the weld pool, and add alloying elements. Two variants exist and shipyards use both.

FCAW-G (gas-shielded) relies on an external shielding gas — most commonly 75% Ar / 25% CO₂ (C25) or straight CO₂ — to protect the molten pool from atmospheric contamination. The flux core still generates slag, but the gas does most of the atmospheric shielding work. FCAW-G produces low spatter, excellent bead appearance, and consistently low hydrogen deposits, making it the first choice for structural fillet welds, groove welds, and outfitting work done inside a covered bay.

FCAW-S (self-shielded) generates all its own shielding from the flux core; no external gas cylinder is required. This makes it highly portable and wind-resistant, suitable for outdoor hull work and areas where dragging a gas hose is impractical. The trade-off is that self-shielded wires generally produce more fume and spatter than gas-shielded wires, and electrode selection matters greatly because hydrogen content and impact toughness vary widely across wire classifications.

AWS A5.20 Wire Classifications

AWS A5.20 covers carbon steel electrodes for FCAW. Reading the classification label tells you everything about how to run the wire.

Always verify wire classification, polarity, and gas requirement on the Welding Procedure Specification (WPS) before striking an arc.

Machine Setup and Parameter Selection

FCAW machines are constant-voltage (CV). You set voltage at the machine and control amperage indirectly by setting wire-feed speed (WFS). Higher WFS = higher amperage = more heat input.

For a typical 0.045-inch E70T-1C wire on 1/2-inch plate:

For E71T-8 self-shielded wire, CTWD is typically longer (up to 1.5 inches) because the extended electrode stickout is part of the shielding mechanism — shortening it can cause porosity.

A flat, uniform bead with minimal spatter is the target. If spatter is excessive, voltage is usually too low. If the bead is tall and narrow (ropy), WFS is too high relative to voltage. Adjust one variable at a time and run a test bead before welding production joints.

Multi-Pass Fillet Welds on T-Joints

Joining 1/2-inch plate in a T-joint configuration requires multiple passes. A WPS will specify the sequence:

1. Root pass — smaller wire-feed speed and voltage to ensure fusion into the joint root without burn-through.

2. Fill passes — increased parameters to build weld size efficiently.

3. Cover (cap) pass — parameters that produce a smooth, flat finished surface.

Between passes, chip and wire-brush all slag completely. Trapped slag is a discontinuity that fails ABS workmanship standards. Use a spatter chipper and wire brush after every pass; verify the surface is clean before depositing the next bead.

Travel angle for fillet welds is typically 40–50° from horizontal (work angle) and 5–15° drag angle for FCAW. Maintain a consistent travel speed — uneven speed causes variable leg lengths, a common rejection reason.

ABS Workmanship Standards — Visual Acceptance Criteria

ABS Rules for Materials and Welding (Part 2, Section 4) set minimum visual acceptance criteria for ship structure welds. Key points for fillet welds:

Self-inspect methodically: use a weld profile gauge for size, a flashlight at a low angle to reveal undercut, and run a gloved finger along toes to feel for overlap or lack of fusion before submitting your coupon.

Safety

FCAW generates significant fume and UV radiation. Before striking an arc:

Key terms10

FCAW-GGas-shielded flux-cored arc welding; uses an external shielding gas (such as 75/25 Ar/CO₂) in addition to the flux core to protect the weld pool from atmospheric contamination.
FCAW-SSelf-shielded flux-cored arc welding; the flux core alone provides all shielding, requiring no external gas supply, making it suitable for outdoor and high-wind shipyard environments.
AWS A5.20The American Welding Society filler metal specification that classifies carbon steel electrodes for flux-cored arc welding, defining mechanical properties, usability, and shielding gas requirements.
Wire-feed speed (WFS)The rate, measured in inches per minute (ipm), at which the electrode wire is fed through the gun; on a CV machine, WFS is the primary control for welding amperage and heat input.
Contact-tip-to-work distance (CTWD)The distance from the end of the contact tip in the welding gun to the workpiece surface; affects current, arc stability, and — for FCAW-S — the effectiveness of flux shielding.
Constant-voltage (CV) machineA welding power source that maintains a preset arc voltage while automatically adjusting current as wire-feed speed changes; the standard power source type for FCAW and GMAW.
UndercutA groove melted into the base metal alongside the weld toe that is not filled by weld metal; a surface discontinuity that reduces cross-sectional strength and is subject to ABS dimensional limits.
WPS (Welding Procedure Specification)A written document that prescribes the essential variables for a weld — including process, filler metal classification, polarity, shielding gas, parameter ranges, and pass sequence — to ensure repeatable quality.
DCEN / DCEPDirect current electrode negative (work is positive) and direct current electrode positive (work is negative); polarity must match wire classification — E71T-8 requires DCEN; E70T-1C and E71T-1C require DCEP.
Multi-pass weldA weld built up in two or more successive passes (root, fill, cap) to achieve the required weld size and mechanical properties on thicker base materials such as 1/2-inch shipbuilding plate.

Worked examples4

1. A WPS calls for a 5/16-inch fillet weld leg. After welding, you measure the weld with a profile gauge and find one leg measures 0.280 inch and the other measures 0.315 inch. Are either leg measurements acceptable?
  1. Step 1 — Convert the specified leg to decimal: 5/16 inch = 0.3125 inch.
  2. Step 2 — Check the first leg: 0.280 inch < 0.3125 inch. The first leg is undersized and does not meet the minimum specified dimension.
  3. Step 3 — Check the second leg: 0.315 inch < 0.3125 inch. 0.315 is less than 0.3125, so this leg is also undersized by 0.3125 − 0.315 = −0.0025 inch... wait — recalculate: 0.315 inch vs. 0.3125 inch. 0.315 > 0.3125, so the second leg exceeds the minimum and is acceptable in size.
  4. Step 4 — Conclusion: The first leg at 0.280 inch is undersized and must be repaired by adding weld metal. The second leg at 0.315 inch meets the minimum.
Answer: The 0.280-inch leg is undersized and rejectable; the 0.315-inch leg meets the 5/16-inch (0.3125-inch) minimum and is acceptable for size.
2. You are running E70T-1C wire at 26 V and 280 ipm WFS. You want to estimate whether increasing WFS to 320 ipm will meaningfully change heat input, given that heat input is proportional to amperage. Your current setting produces approximately 220 A. The higher WFS is expected to produce approximately 255 A at the same voltage. Calculate the percentage increase in amperage.
  1. Step 1 — Identify the two amperage values: original = 220 A, new = 255 A.
  2. Step 2 — Find the difference: 255 − 220 = 35 A.
  3. Step 3 — Calculate percentage increase: (35 ÷ 220) × 100 = 15.9%, approximately 16%.
Answer: Increasing WFS from 280 ipm to 320 ipm raises amperage by approximately 35 A, a roughly 16% increase, which will noticeably increase heat input and bead width — verify the new parameter set still meets WPS limits before running production welds.
3. Your shielding gas regulator shows a flow rate of 30 CFH, but the WPS specifies 35–45 CFH for E70T-1C. During welding you notice scattered porosity on the bead surface. By how many CFH must you increase flow to reach the midpoint of the specified range?
  1. Step 1 — Find the midpoint of the specified range: (35 + 45) ÷ 2 = 40 CFH.
  2. Step 2 — Find the required increase: 40 − 30 = 10 CFH.
  3. Step 3 — Verify 40 CFH falls within the 35–45 CFH range: yes, it is centered in the range.
Answer: You must increase flow by 10 CFH, from 30 CFH to 40 CFH, to reach the midpoint of the specified range. Insufficient shielding gas flow is a common cause of surface porosity in FCAW-G.
4. A multi-pass T-joint fillet weld requires three passes: root, fill, and cap. The WPS specifies a minimum of two minutes inter-pass cooling time between each pass on 1/2-inch plate. If the root pass is completed at 9:04 AM, the fill pass at 9:18 AM, and the cap pass at 9:29 AM, did the welder observe the required inter-pass cooling times?
  1. Step 1 — Measure time between root and fill passes: 9:18 AM − 9:04 AM = 14 minutes. 14 minutes ≥ 2 minutes minimum — acceptable.
  2. Step 2 — Measure time between fill and cap passes: 9:29 AM − 9:18 AM = 11 minutes. 11 minutes ≥ 2 minutes minimum — acceptable.
  3. Step 3 — Both inter-pass intervals exceed the 2-minute minimum.
Answer: Yes, both inter-pass cooling intervals (14 minutes and 11 minutes) exceed the 2-minute minimum specified by the WPS. The welder is in compliance.

The math in this lesson2

Learners compute heat input as volts × amps × 60 ÷ travel speed to compare WFS settings.
A-SSE.1N-Q.3
Brush up in the math halls at newSchoolWorks.com:
In class: Wire and shielding gas selection exercise: students match three FCAW wire classifications (E70T-1C, E71T-1C, E71T-8) to their shielding gas requirements, polarity, and typical shipyard application using AWS A5.20 filler metal specification and record findings in a comparison table. · Machine parameter optimization drill: working in pairs, students run test beads at three different wire-feed speeds and two voltage settings, measure bead width and height with a weld profile gauge, and identify the parameter set producing the flattest, most uniform bead with minimal spatter. · Production simulation: students complete a multi-pass fillet weld joining 1/2-inch plate T-joint using FCAW-G with specified root and fill passes per a provided WPS, then self-inspect using the ABS workmanship checklist and submit the coupon with a completed inspection report.
Materials: CV welding machines with wire feeders, E70T-1C wire (gas-shielded), E71T-8 wire (self-shielded), 75/25 Ar/CO2 shielding gas cylinders with regulators, 1/2-inch carbon steel plate, weld profile gauges, spatter chippers, wire brush, ABS Rules for Materials and Welding Part 2 Section 4 excerpt, WPS documents, lab log notebooks, PPE
Check: Students submit a completed 1/2-inch multi-pass T-joint fillet coupon with a self-inspection report; instructor confirms visual acceptance per ABS criteria and verifies lab log entries for parameter sets are complete. Both required for credit.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

NCCER Shipfitting / NCCER Maritime Welding — process setup
1. An E71T-8 electrode is connected to DCEP instead of the required DCEN. What is the most likely result when welding begins?
AWS D1.1 Certified Welder — filler metal specification
2. According to AWS A5.20, which shielding gas is designated by the suffix 'C' in a wire classification such as E70T-1C?
NCCER Maritime Welding — equipment operation
3. A welder sets voltage to 26 V and increases wire-feed speed from 250 ipm to 350 ipm on a CV machine. What effect should the welder expect on the weld bead?
ABS/USCG Weld Test — workmanship standards
4. When performing a multi-pass FCAW fillet weld, why must all slag be completely removed between passes?
NCCER Maritime Welding — parameter optimization
5. A FCAW-G bead shows excessive spatter and a narrow, convex profile. Which parameter adjustment is most likely to correct both problems?
NCCER Shipfitting / AWS D1.1 Certified Welder — filler metal selection
6. Which FCAW wire classification from AWS A5.20 is best suited for vertical-up welding outdoors on a ship hull where external shielding gas cannot be reliably maintained?
AWS D1.1 Certified Welder / ABS/USCG Weld Test — discontinuity identification
7. During FCAW-G welding, a welder notices surface porosity appearing on multiple beads despite correct voltage and wire-feed speed. The most likely cause is:
NCCER Maritime Welding / NCCER Shipfitting — safety
8. Before changing a wire spool on a FCAW machine, the correct safety action is to:
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