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newSchoolWorks.com › VoTechWorks › Building & Construction › Welding › Flux-Cored Arc Welding (FCAW) › Lesson 4
BLD-WELD01-05 · Lesson 4 · 12 clock hours · lab

Flat and Horizontal Groove Welds (1G and 2G)

Objective. Students will produce a complete-joint-penetration V-groove weld on carbon steel plate in the 1G and 2G positions using a backing bar, meeting AWS D1.1 visual acceptance criteria for reinforcement, fusion, and profile.

Flat and Horizontal Groove Welds (1G and 2G) with FCAW

Flux-cored arc welding (FCAW) is the workhorse of structural steel fabrication. Its high deposition rate, tolerance for mill scale, and ability to run outdoors make it the dominant process on bridge and building projects governed by AWS D1.1. This lab focuses on complete-joint-penetration (CJP) V-groove welds in the flat (1G) and horizontal (2G) positions — two of the most commonly tested positions on the AWS D1.1 Certified Welder exam.

Joint Setup and Fit-Up

The joint used in this lab is a single-V groove with a 60° included angle (30° bevel on each plate face), a 1/8 in. root opening, and a backing bar. The backing bar is a piece of 3/8 in. × 1 in. A36 flat stock tack-welded flush to the bottom of both plates. It performs two functions: it supports the molten weld pool so the root pass achieves full penetration, and it eliminates the need for a back-gouge — making CJP welds faster and more consistent in production.

Fit-up accuracy is not optional. Check the root opening at both ends and at mid-length with a fit-up square and ruler before tacking. A root opening that is too tight restricts penetration; one that is too wide produces an irregular root bead and wastes filler metal. Tack at least two places — typically near each end — using the same E71T-1C wire and shielding gas you will weld with. Tacks must be sound; a cracked tack becomes a defect in the finished weld.

Shielding Gas and Wire Selection

E71T-1C wire is an AWS A5.20 classification. Breaking down the designation: E = electrode, 7 = 70 ksi minimum tensile strength, 1 = all-position capability, T = tubular (flux-cored), 1 = usability designator (spray-transfer characteristics, flat and horizontal optimized), C = designed for 100% CO₂ shielding. In this lab the mix is 75% Ar / 25% CO₂, which is also acceptable for the -1 designator and produces slightly less spatter than straight CO₂. Always verify your wire spool label matches the WPS before striking an arc.

Welding Parameters and Bead Sequence

A constant-voltage (CV) power source controls arc length automatically through self-regulation. Set voltage and wire-feed speed (which sets amperage) to the ranges specified on the Welding Procedure Specification (WPS) for 0.045 in. wire on 3/8 in. plate. Typical ranges for E71T-1C at this diameter run in the low-to-mid range of the wire manufacturer's published data; always defer to your school's qualified WPS.

Root pass: Use a slightly lower heat input to avoid burning through the narrow root opening. Keep the gun angle at roughly 90° to the joint (work angle) with a 5–10° drag (travel angle). Maintain a consistent travel speed to produce a flat, slightly convex bead that fuses to both sides of the groove and to the backing bar.

Fill passes: Increase parameters slightly for faster deposition. Use a stringer or narrow weave; avoid wide weaves that trap slag. Clean each pass with a chipping hammer and wire brush before depositing the next one. In the 2G position, place the first fill pass against the bottom plate shelf (toe), then step up — this prevents overlap and lack-of-fusion on the lower toe.

Cover pass: The final layer must meet visual acceptance criteria. Aim for a flat to slightly convex profile. Face reinforcement must not exceed 3/16 in. above the base-metal surface per AWS D1.1. Undercut at the toes must not exceed the D1.1 limits for the applicable condition.

Controlling Distortion and Interpass Temperature

Heat input from multi-pass welding causes angular distortion. Tacking the joint in a slight negative angle (pre-setting) before welding compensates for pull. Alternating passes symmetrically — when joint design allows — also helps.

Interpass temperature is the temperature of the base metal immediately before each subsequent pass is deposited. Measure it with a contact thermometer at a point within 1 in. of the joint. The WPS specifies a maximum interpass temperature (commonly 400–500 °F for mild steel, but use the value on your WPS). Exceeding it can degrade mechanical properties and increase distortion. Record every reading in your lab log with the pass number and time.

Safety

Key terms10

Complete-joint-penetration (CJP) weldA groove weld in which fusion extends through the entire thickness of the joint, required when the weld must develop the full strength of the base metal.
1G positionFlat welding position for groove welds; the plate lies horizontal and the weld is deposited from above, allowing gravity to help support the pool.
2G positionHorizontal welding position for groove welds; the joint axis is horizontal and the weld face is vertical, requiring the welder to control pool sag.
Backing barA piece of steel placed behind the root of a groove joint to support the molten pool during the root pass and ensure full penetration without a back-gouge.
E71T-1CAn AWS A5.20 flux-cored electrode classification indicating 70 ksi tensile strength, all-position capability, tubular construction, and suitability for CO₂ or mixed shielding gas.
Interpass temperatureThe temperature of the base metal measured immediately before depositing the next weld pass; must stay within WPS limits to preserve mechanical properties.
Face reinforcementThe height of weld metal above the plane of the base-metal surface on the face side of a groove weld; AWS D1.1 limits this to prevent stress concentration.
Root openingThe gap between the two base-metal pieces at the root of the joint before welding; controls penetration and affects fusion to the backing bar.
UndercutA groove melted into the base metal at the weld toe that is not filled by weld metal; a discontinuity that AWS D1.1 limits in depth and length.
Constant-voltage (CV) power sourceA welding machine that maintains a nearly steady output voltage while amperage varies automatically with wire-feed speed, the standard power source for FCAW and GMAW.

Worked examples4

1. After welding, you measure face reinforcement with a groove weld gauge. The gauge reads 7/32 in. above the plate surface. Does this coupon pass the AWS D1.1 visual criterion for face reinforcement?
  1. Recall the AWS D1.1 maximum face reinforcement for a groove weld: 3/16 in.
  2. Convert 3/16 in. to thirty-seconds for comparison: 3/16 = 6/32 in.
  3. The measured value is 7/32 in., which is greater than 6/32 in. (3/16 in.).
  4. Because the measurement exceeds the maximum allowed, the coupon does not pass this criterion.
Answer: No. 7/32 in. exceeds the 3/16 in. (6/32 in.) limit. The cover pass must be ground down until reinforcement is at or below 3/16 in., then re-inspected.
2. Your WPS specifies a root opening of 1/8 in. You fit up the joint and measure 3/32 in. at one end and 5/32 in. at the other end. By how much does each end deviate from the target, and which deviation is more critical for weld quality?
  1. Convert all values to thirty-seconds: target = 4/32 in., measured ends = 3/32 in. and 5/32 in.
  2. Deviation at tight end: 4/32 − 3/32 = 1/32 in. too tight.
  3. Deviation at wide end: 5/32 − 4/32 = 1/32 in. too wide.
  4. Assess which is more critical: a tight root opening restricts penetration and risks incomplete joint penetration at the root, which is a structural defect. A slightly wide opening increases the risk of burn-through or an irregular root bead but is easier to control with technique.
  5. Both ends deviate by the same amount (1/32 in.), but the tight end poses the greater risk of a CJP defect.
Answer: Each end deviates 1/32 in. from the target. The tight end (3/32 in.) is more critical because restricted root opening can cause incomplete penetration, a rejectable discontinuity under AWS D1.1.
3. You have completed the root pass and two fill passes. Before starting the third fill pass, you measure the interpass temperature as 460 °F. Your WPS lists a maximum interpass temperature of 400 °F. How long should you wait if the plate cools at approximately 20 °F per minute?
  1. Determine how many degrees the plate must cool: 460 °F − 400 °F = 60 °F.
  2. Divide the required temperature drop by the cooling rate: 60 °F ÷ 20 °F per minute = 3 minutes.
  3. Wait at least 3 minutes, then re-measure with the contact thermometer before welding.
Answer: Wait at least 3 minutes (cooling 60 °F at 20 °F/min), then verify the temperature is at or below 400 °F before depositing the next pass.
4. A V-groove joint has a 60° included angle and a root opening of 1/8 in. What is the bevel angle on each plate face?
  1. The included angle is the total angle across the joint: 60°.
  2. Because both plates are beveled equally, divide by 2: 60° ÷ 2 = 30° per side.
  3. Confirm: 30° + 30° = 60° included angle — correct.
Answer: Each plate face is beveled at 30°. This is a standard single-V groove geometry referenced in AWS D1.1 joint details.

The math in this lesson2

Learners check reinforcement and root-opening deviations in fractions and halve a 60° included angle to find bevel angle.
7.G.5N-Q.3
Brush up in the math halls at newSchoolWorks.com:
In class: Instructor demonstrates fit-up and tack welding of a V-groove (60° included angle, 1/8 in. root opening) on backing bar, then completes a full multi-pass sequence (root, fill, cover) explaining bead sequencing to control distortion. · Students fit, tack, and weld one 1G groove coupon and one 2G groove coupon, recording interpass temperatures with a contact thermometer and noting readings in their lab log; instructor spot-checks that interpass temperature does not exceed WPS maximum. · Students grind flush any excess reinforcement and perform a self-inspection using a groove weld gauge and AWS D1.1 visual criteria checklist before submitting coupons to the instructor.
Materials: CV power source, wire feeder, E71T-1C .045 in. wire, 75%Ar/25%CO2, 3/8 in. A36 plate pre-beveled to 30° per side, 3/8 in. x 1 in. backing bar stock, contact thermometer, groove weld gauge, AWS D1.1 visual acceptance criteria card, fit-up square, C-clamps, angle grinder
Check: One 1G and one 2G groove coupon inspected by instructor; pass requires face reinforcement ≤3/16 in., no undercut exceeding D1.1 limits, complete fusion visible at toes, and no cracks; 100% pass required.

Practice check8

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

AWS D1.1 Certified Welder — Visual Inspection
1. Which AWS D1.1 visual acceptance criterion applies to face reinforcement on a groove weld in this lab?
NCCER Welding — FCAW Technique
2. In the 2G (horizontal) welding position, where should the first fill pass be placed to prevent incomplete fusion at the lower toe?
AWS SENSE L1-2 — Filler Metals
3. What does the 'C' suffix in the electrode designation E71T-1C indicate?
AWS D1.1 Certified Welder — Discontinuities and Defects
4. A student finishes the root pass and immediately begins depositing the first fill pass without cleaning the bead. What is the most likely result?
NCCER Welding — Welding Procedures
5. Why is a contact thermometer used during multi-pass groove welding?
AWS D1.1 Certified Welder — Joint Preparation
6. A backing bar is used in this lab's groove joint primarily to:
AWS SENSE L1-2 — Safety and Health
7. Which PPE item is required in addition to a welding helmet when operating an angle grinder to remove excess reinforcement?
NCCER Welding — FCAW Technique
8. During a 2G groove weld, a student notices the weld pool sagging toward the lower plate, creating an overlap at the bottom toe. The BEST corrective action is to:
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