GTAW Root / SMAW Fill – 5G Fixed Position

GTAW Root / SMAW Fill – 5G Fixed Position

What the 5G Position Means

In the 5G position, the pipe axis runs horizontally and the pipe is fixed — it cannot be rotated during welding. You weld the entire joint by moving yourself and your torch or electrode around the pipe. Think of the pipe end as a clock face: 12 o'clock is at the top, 6 o'clock is at the bottom, 3 o'clock is on the right side, and 9 o'clock is on the left. Every clock position presents a different gravitational challenge — overhead at the bottom, vertical on the sides, flat near the top — all in a single joint. Mastering 5G prepares you for structural pipe and pressure piping work in the field, where repositioning is rarely an option.

Joint Setup and Back-Purge

Schedule-80 carbon-steel pipe has thick walls, so proper fit-up is critical. A consistent root opening (gap) and land (root face) allow the GTAW root pass to fuse both pipe walls completely. Before striking an arc, purge the inside of the pipe with argon. Back-purging prevents atmospheric oxygen from contacting the hot root bead on the inside surface, which would cause oxidation and porosity. Seal the pipe ends loosely — enough to hold purge pressure but with a small vent so argon can flow through and displace air. A purge flow is maintained throughout the entire root pass. Verify purge is established before you begin.

Safety First

• PPE: Full leather welding jacket, leather gloves, and a welding helmet with the correct lens shade for both GTAW (typically shade 8–13 depending on amperage) and SMAW. Shade selection follows the manufacturer's guide and ANSI Z49.1 recommendations.
• Hot work awareness: Schedule-80 pipe retains heat for a long time. Use insulated clamps and never grab bare pipe between passes.
• Argon hazard: Argon is colorless, odorless, and heavier than air. In confined or low spaces it can displace oxygen. Ensure ventilation is adequate; know the location of the area's fresh-air supply.
• Fume control: SMAW with E6010 and E7018 generates significant fume. Use local exhaust ventilation (LEV) at the source and position yourself upwind or cross-draft of the plume.
• Lockout/Tagout: Follow your facility's LOTO procedure whenever you service, adjust, or clear a jam in a power source. Never assume equipment is de-energized without verifying.
• Hot slag: After each SMAW pass, chip slag away from yourself. Slag can pop and travel several feet.

GTAW Root Pass Technique

ER70S-2 filler, 3/32-inch diameter, is the standard choice for open-root carbon-steel pipe because its triple-deoxidizer chemistry tolerates minor mill scale and moisture. Set your GTAW machine to DCEN (direct current electrode negative) for a stable arc. Arc length should equal approximately the diameter of the tungsten — keep it tight and consistent.

Begin at the 6 o'clock position on one side and weld uphill to 12 o'clock, then repeat on the other side. This upward progression at the sides and bottom gives the molten puddle gravity support and promotes full penetration. At the 12 o'clock position, blend the two weld starts carefully to avoid a cold lap. Watch for the "keyhole" — a small, round opening at the leading edge of the puddle that confirms full penetration. If the keyhole closes, slow your travel; if it grows too large, increase travel speed or reduce amperage slightly.

Torch angle changes with clock position:

• 6 o'clock (overhead): Work angle approximately 90° to the pipe axis; slight push angle.
• 3 and 9 o'clock (vertical sides): Tilt the torch slightly upward (drag angle toward the direction of travel) to keep the puddle from sagging.
• 12 o'clock (flat/top): Standard forehand angle; the puddle is most manageable here.

E6010 Hot Pass

After the root, wire-brush and inspect for any high spots or cold laps. The hot pass with E6010 (3/32-inch, DCEP) burns in just deep enough to wash out any root oxidation or suck-back without adding significant fill. Travel fast enough that you are not building a large bead — the goal is a clean, fusion-verified tie-in to the root.

E7018 Fill and Cap Passes

E7018 (1/8-inch, DCEP) is a low-hydrogen electrode that provides the strength and toughness required for structural and pressure pipe. Keep rods in a rod oven or sealed container and limit exposure to shop air; absorbed moisture can cause hydrogen-induced cracking or porosity.

Fill passes are stringer or slight weave beads. Maintain interpass temperature — allow the pipe to cool to the maximum interpass temperature specified by your WPS before depositing the next pass; for mild steel this is typically no higher than 400 °F (204 °C) unless the WPS states otherwise. Check with an infrared thermometer or temperature-indicating stick.

The cap pass must blend smoothly into the base metal on both toes. Crown height (reinforcement) must not exceed the limit in AWS D1.1 Table 8.1 for the applicable pipe wall thickness. Undercut at the toe must not exceed the allowed depth.

Visual Inspection — AWS D1.1 Criteria

After cleaning, inspect the completed joint under bright light, using a mirror for the 6 o'clock inside surface where accessible. Use a fillet/groove weld gauge to measure cap reinforcement. Look for:

• Cracks — not permitted anywhere.
• Incomplete fusion or overlap — not permitted.
• Porosity — subject to frequency and size limits in D1.1.
• Undercut — limited in depth per D1.1.
• Cap reinforcement — must be within the code-specified maximum.

Document every finding on your AWS D1.1 visual checklist before calling the instructor for sign-off.