Multi-Position GTAW on Carbon Steel Plate (2G, 3G, 4G)

Multi-Position GTAW on Carbon Steel Plate (2G, 3G, 4G)

Gas Tungsten Arc Welding (GTAW) demands precise hand coordination at all times, but that demand multiplies when you leave the flat position. Gravity acts differently on the weld puddle in every position, and your torch angle, travel speed, and amperage must compensate. This lesson covers the three test positions you will practice and be evaluated on: 2G (horizontal groove), 3G (vertical groove), and 4G (overhead groove).

Why Position Matters

In the flat (1G) position, gravity helps keep the molten puddle in the joint. As soon as you tilt the work or weld overhead, gravity becomes your opponent. The puddle wants to sag, drip, or undercut the top toe of the weld. Controlling heat input and travel speed is how you win that fight. Amperage that works perfectly flat will likely cause sagging or burn-through in overhead because the puddle is less stable without gravity supporting it.

2G — Horizontal Groove Weld

In the 2G position the plate is vertical and the groove runs horizontally. The puddle tends to sag downward toward the lower edge of the joint. Counter this by:

• Tilting the torch slightly upward (roughly 5–15° above horizontal, pointing into the joint) so arc force pushes the puddle back into the groove.
• Keeping travel speed slightly faster than flat so the puddle does not build up and roll over the lower bevel face.
• Using a slight whip or pause-and-advance technique to allow the puddle to freeze between filler additions.

Watch the lower toe constantly — undercut there is a common rejection cause on bend tests.

3G — Vertical Groove Weld (Uphill)

In the 3G position the plate is vertical and you travel upward. Uphill progression gives better fusion and is the standard for structural code work. The puddle tries to run down and away from the arc. Control it by:

• Pointing the torch downward into the puddle at roughly 5–15° below horizontal (slightly uphill-angled) so arc force holds the puddle in place.
• Using a controlled triangular or shelf-building weave: let a small shelf freeze, then advance; this ladders the bead up the joint without sagging.
• Reducing amperage 5–10% compared to flat to keep the puddle stiffer.
• Pausing at each toe to ensure fusion before moving back to center.

If the puddle starts to drip or look glassy and fluid, lift the arc slightly or increase travel speed momentarily.

4G — Overhead Groove Weld

Overhead is the most demanding position. The puddle has no gravity support at all and will fall if heat input is too high. Key adjustments:

• Reduce amperage further — often 10–15% below flat settings — and use the foot pedal to back off instantly if the puddle looks wet or starts to drop.
• Keep the arc length very short. A long arc in GTAW overhead means a wider, hotter, less controllable puddle.
• Use small filler rod additions frequently rather than large additions that overheat the puddle.
• Wear leather sleeves and a full-coverage welding jacket — spatter and dripping hot metal are real hazards here.
• Position yourself so your torch arm is supported against your body or the table edge; fatigue causes arc length drift.

Guided-Bend Testing

After welding, selected coupons are cut and bent using the school's guided-bend jig. Face-bend specimens are bent with the face (crown) in tension; root-bend specimens are bent with the root in tension. AWS D1.1 visual and bend acceptance criteria require that after bending, no single open defect exceed 1/8 in. (3 mm) in any direction, and the sum of all defects on any single face must not exceed 3/8 in. You will record every measurement in your weld log.

When a coupon fails, the failure is almost always traceable to one of these causes: lack of fusion at the root or toes, porosity from contamination or insufficient gas coverage, or incomplete penetration from moving too fast or carrying too long an arc.

Root-Cause Analysis

Every failed bend test is a learning event, not just a mistake. For each failure, write two sentences in your weld log: the first identifies the defect and its probable cause; the second states the technique correction. Example: "Root porosity appeared on the face-bend specimen, likely caused by a gas lens blockage that reduced argon coverage at the root. Corrective action: inspect and clean the gas lens before each session and verify flow rate at the regulator."

Safety Requirements for This Lesson

PPE: Auto-darkening helmet (shade 9–13 for GTAW on steel), leather welding gloves, leather jacket or sleeves (mandatory in overhead), flame-resistant pants, leather boots — no synthetic materials near the arc.

Argon cylinders: Secure cylinders to the cart or wall bracket at all times. Inspect the regulator for damage before opening the valve. Open the cylinder valve slowly and stand to the side.

Grinder safety: When using the angle grinder with a flap disc to clean coupons between passes, wear a face shield over your safety glasses, not a helmet. Keep the flap disc guard in place.

Hot metal: Coupons reach temperatures that cause serious burns long before they glow visibly. Use tongs or pliers to handle all coupons; mark hot pieces with chalk. Never lay a hot coupon on anything flammable.

Ventilation: GTAW on carbon steel with ER70S-2 still produces metal fume. Use local exhaust ventilation at each station and keep your head out of the fume plume.