SMAW Fill and Cap Passes – 1G and 2G Positions

SMAW Fill and Cap Passes – 1G and 2G Positions

Why Fill and Cap Passes Matter

Once the root pass is complete and the groove is opened up, fill passes build the joint to near-flush, and the cap pass finishes the surface. The cap pass is what inspectors see first, and it must meet every visual acceptance criterion in AWS D1.1 before any further testing begins. A structurally sound root can still fail inspection because of a sloppy cap. In pipe welding, this is especially important because the weld must perform under pressure, vibration, and temperature cycling throughout the life of the structure.

Joint Preparation and Electrode Selection

For both the 1G (pipe horizontal, rotated) and 2G (pipe vertical axis, fixed) positions, you will use E7018 low-hydrogen electrodes. The "70" designates a minimum tensile strength of 70,000 psi; the "18" indicates low-hydrogen flux and suitability for DC+ (electrode positive) operation. Low-hydrogen electrodes are mandatory for structural pipe work covered by AWS D1.1 because hydrogen-induced cracking is a primary failure mode in higher-strength steels.

Rod oven storage is not optional. E7018 electrodes absorb atmospheric moisture rapidly once exposed. Store them in a rod oven at the manufacturer-specified temperature (check the electrode data sheet — typical ranges are published by the electrode manufacturer, not estimated here). Electrodes left out longer than the manufacturer allows must be reconditioned or discarded. Moisture in the flux produces hydrogen porosity and can cause delayed cracking that does not show up until the weld has cooled.

Use 1/8 in electrodes for fill passes where groove width and access are limited. Step up to 5/32 in for later fill passes and the cap when you have full access and need better deposition rates. Confirm that your amperage setting is within the electrode manufacturer's recommended range for the diameter you are running.

Interpass Cleaning and Temperature

Before each fill pass, chip all slag completely and wire-brush the bead. Any slag inclusion bridged over by the next pass will show up on radiography and cause rejection. Use your chipping hammer with eye protection in place — hot slag travels. Check the interpass temperature: for carbon steel pipe, AWS D1.1 specifies a maximum interpass temperature; exceeding it can reduce toughness in the heat-affected zone. Use a contact or infrared thermometer, not your bare hand.

1G Position: Technique for Fill and Cap

In 1G, the pipe rotates on pipe stands so the weld puddle is always in a comfortable flat or slightly downhill position. This is the most forgiving position for fill and cap because gravity works in your favor.

• Stringer beads are preferred for fill passes: narrow, controlled, and less prone to slag entrapment. Maintain a short arc length — roughly equal to the electrode diameter.
• Weave beads are acceptable for the cap when you need to cover a wide groove opening, but keep the weave width to no more than 2.5 times the electrode core diameter to control heat input and avoid undercut at the toes.
• Rotate the pipe steadily so the puddle stays at or just past the 12 o'clock position. Pause rotation if the puddle runs ahead.
• Watch both toes of the cap bead. Insufficient tie-in at the toes causes undercut or overlap — two of the most common reasons a cap fails visual inspection.

2G Position: Adjustments Required

In 2G, the pipe axis is vertical and fixed; you weld around the pipe in the horizontal position. Gravity tries to pull the puddle downward, causing sag, overlap on the lower toe, and undercut on the upper toe.

• Reduce amperage compared to 1G — a typical starting point is 5–15 A lower, but dial it in based on puddle behavior.
• Increase travel speed slightly to prevent the puddle from getting too large.
• Hold a slight upward electrode angle (drag angle toward the upper side of the groove) to support the puddle against gravity.
• Use stringers rather than wide weaves. Multiple stringer passes give you better control of each bead than one wide weave that can sag.
• Document every amperage and travel-speed change in your weld log. This record becomes part of your welding procedure qualification data and builds the habit required for code work.

AWS D1.1 Visual Acceptance Criteria for Cap Passes

Inspect every completed coupon against the following minimums before calling the instructor:

• Reinforcement height: The cap must not exceed 3/16 in above the base metal surface.
• Undercut: No undercut deeper than 1/32 in along either toe.
• Overlap: No cold lap where the weld metal rolls over without fusing to the base metal.
• Cracks: None permitted — any crack is automatic rejection.
• Surface porosity: No visible porosity on the cap face.

Use a fillet weld gauge to check reinforcement height objectively. Visual estimates are not reliable; the gauge is.

Safety Points

• PPE: Full leather gloves, leather jacket or sleeves, welding helmet (shade appropriate for the amperage), leather boots, and hearing protection when chipping. Pipe stands and rotating equipment can pinch fingers — keep clear during rotation.
• Fume control: Pipe welding concentrates fumes inside the groove. Position local exhaust ventilation at the source or use a supplied-air respirator in confined or low-ventilation areas. E7018 flux produces manganese-bearing fumes; chronic overexposure is a recognized health hazard.
• Hot work: Pipe coupons retain heat long after welding stops. Use pipe tongs or insulated gloves when repositioning. Mark hot coupons with soapstone as a warning to others.
• Electrical safety: Inspect the electrode holder, cable, and work clamp connection before starting. A loose work clamp causes arc blow, poor fusion, and a shock hazard.