Stick Welding Pipe: Root Pass, Hot Pass, Fill & Cap Technique

Pipe welding with stick electrodes follows a specific sequence: E6010 root pass to achieve full penetration through the open root, a hot pass with 6010 to clean up the root, then E7018 fill and cap passes for strength and appearance. Each pass has its own technique, amperage setting, and rod manipulation pattern.

This procedure applies to carbon steel pipe (A106, A53) in the 5G (fixed horizontal) and 6G (fixed 45-degree) positions, which are the standard certification tests and the most common field configurations. Schedule 40 and schedule 80 pipe in the 2" to 12" diameter range use this same basic approach.

Joint Preparation

Bevel and Root Face

Standard pipe bevel for SMAW is a 37.5-degree bevel on each side (75-degree included angle) with a 1/16" to 3/32" root face (land). The root face is the small flat area at the bottom of the bevel that the arc burns through during the root pass.

• Root face too thick (over 3/32"): The arc can’t burn through, resulting in lack of penetration
• Root face too thin (under 1/16"): Burns away too easily, making the keyhole hard to control
• Inconsistent root face: Creates hot spots and cold spots around the pipe

Use a beveling machine or grinder to achieve a consistent bevel and land. File the root face to uniform thickness. An inconsistent root face is the most common setup problem in pipe welding.

Root Opening (Gap)

Set the root opening at 3/32" to 1/8" for 1/8" E6010 with standard technique. Some welders prefer a wider gap (up to 5/32") depending on their technique and the pipe wall thickness.

Use spacer wire or small tack weld buildup to maintain consistent gap around the pipe. The gap tends to close as you tack, so check it at multiple points.

Tack Welds

Place four tack welds at the 12, 3, 6, and 9 o’clock positions. Each tack should be about 1/2" to 3/4" long and feathered (ground thin) at both ends so the root pass can transition smoothly through them.

Tacks that are too thick create high spots that the root pass has to burn through, potentially causing lack of fusion. Tacks that are too thin crack from the thermal stress of the root pass. Grind the tack ends to a thin feathered edge that the incoming root bead can absorb.

The Root Pass (E6010)

The root pass is the most critical and most difficult pass in pipe welding. It must achieve full penetration through the root opening, fuse to both pipe walls, and leave a uniform root reinforcement on the inside of the pipe.

Settings

The Keyhole Technique

The keyhole is a small, bright opening at the leading edge of the weld puddle that indicates full root penetration. It forms when the arc burns through the root face and root opening, creating a hole that molten metal fills as the arc moves forward.

Starting the keyhole:

1. Strike the arc on one side of the joint at the starting position
2. Bring the rod into the root opening
3. Hold steady until you see the root faces melt and a small bright spot appears at the leading edge of the puddle
4. That bright spot is the keyhole. It should be roughly the diameter of the electrode core wire (about 3/32" to 1/8")

Maintaining the keyhole:

The keyhole should stay consistent in size as you travel around the pipe. It’s your real-time indicator of penetration:

• Keyhole too large: Too much heat. You’re blowing through the root. Reduce amps by 5 or increase travel speed slightly.
• Keyhole too small or closes: Not enough heat. The root face isn’t fully melting. Increase amps by 5 or slow down.
• Keyhole disappears: You’ve lost penetration. Stop, grind back to good metal, and restart.

Whip-and-Pause on the Root

The whip-and-pause technique controls heat input and lets the puddle freeze between additions of metal. On the root pass:

1. Establish the keyhole
2. Whip the rod forward 1/4" to 3/8" beyond the leading edge of the puddle
3. Pause for approximately 1 second (let the puddle freeze)
4. Return the rod to the leading edge of the solidified puddle
5. Push the keyhole forward and add metal
6. Whip again and repeat

The rhythm is: burn, whip, pause, return, burn. Each cycle advances the bead about 1/8". The pause is where the puddle freezes and forms the root reinforcement (the bead visible on the inside of the pipe). Too short a pause produces excessive root reinforcement (too much metal inside). Too long a pause causes cold lap where the returning arc can’t fuse to the solidified puddle.

Clock Position Adjustments

Pipe welding requires adjusting your technique as you travel around the pipe because gravity’s effect on the puddle changes continuously.

12 o’clock (flat): Highest amperage in the range (85-90A). The puddle is in flat position and gravity holds it in. Standard whip-and-pause timing.

3 o’clock and 9 o’clock (horizontal): Mid-range amperage (80-85A). The puddle wants to sag. Angle the rod slightly upward (5 degrees) to counteract gravity.

6 o’clock (overhead): Lowest amperage in the range (75-80A). The puddle hangs from the joint. Tighten the arc, shorten the whip distance to 1/4", and increase the pause time slightly so the puddle freezes before it drips.

Transition zones (1-2, 4-5, 7-8, 10-11 o’clock): Gradually adjust amperage and technique between the cardinal positions. Some welders adjust the machine 5 amps between the top and bottom halves. Others run a fixed amperage and adjust their speed and arc length instead.

Uphill vs Downhill Root

Two schools of technique exist for the root pass:

Uphill root (vertical-up): Start at 6 o’clock and weld up to 12 o’clock, one side at a time. Common in pressure piping and code work. Slower but produces more consistent penetration.

Downhill root (vertical-down): Start at 12 o’clock and weld down to 6 o’clock. Faster, used extensively in cross-country pipeline welding. Requires more skill and a different rod manipulation. See E6010 Downhill Root Pass for the specific technique.

The Hot Pass

The hot pass runs immediately after the root pass. Its job is to burn out any slag trapped in the root crown, smooth irregularities, and add a thin layer of metal that serves as the foundation for fill passes.

Settings

The hot pass runs hotter and faster than the root. It needs to melt into the root crown and fuse out any trapped slag. Travel speed is about 30-50% faster than the root pass.

“Hot” means hot. Don’t baby the hot pass. It needs to fully remelt the surface of the root pass. If you run it too cold, you’ll trap slag between the root and fill, creating inclusions that show up on X-ray.

Clean the root pass thoroughly before the hot pass. Chip all slag and wire-brush the crown. Any remaining slag on the root surface will get trapped under the hot pass.

Some procedures specify E7018 for the hot pass. In that case, run it at the upper end of the 7018 range for the diameter and use a slight weave to cover the full width of the root crown.

Fill Passes (E7018)

Fill passes build up the weld to within 1/32" to 1/16" of the pipe surface. They use E7018 for its strength, smooth arc, and low-hydrogen properties.

Settings

Fill Pass Strategy

The groove is wider at the top (near the pipe surface) and narrower at the root. Fill passes build up in layers, each one wider than the last.

• First fill pass: Slightly wider than the hot pass. May be a single stringer bead on small pipe or two side-by-side stringers on large pipe.
• Middle fill passes: Gradually widen to cover the beveled faces. Use multiple stringer beads side by side, overlapping each previous bead by 1/3 to 1/2.
• Final fill pass: Brings the weld level to 1/32" to 1/16" below the pipe surface to leave room for the cap.

Each fill pass must fuse to the sidewalls of the bevel. If you see a “valley” between the bead and the sidewall, you’ve got a fusion issue. Slow down, increase amps slightly, or adjust your rod angle to push the arc into the sidewall.

Clean every fill pass completely before the next. Overhead positions trap slag in the valleys between beads. Chip and brush, then visually inspect and feel for any remaining slag before welding the next pass.

Cap Pass (E7018)

The cap pass is the final, visible layer. It must cover the beveled area completely, extend 1/16" to 1/8" beyond the bevel edge on each side, and show a smooth, slightly convex profile.

Settings

The cap typically uses a slight weave to cover the full groove width. Pause at each toe for 1-2 seconds to build up the edge and prevent undercut. Cross through the center at a steady speed. The finished cap should have a uniform width, consistent crown height of about 1/16" to 3/32" above the pipe surface, and no undercut.

On small-diameter pipe (2"-4"), a single cap bead may cover the groove. On larger pipe, you’ll run multiple cap beads side by side, overlapping each by about 1/3.

Common Pipe Welding Problems

Lack of root penetration (no keyhole): Root face too thick, amperage too low, or gap too narrow. Grind the root face thinner, increase amps by 5, or widen the gap (which may require re-tacking).

Root suck-back (concave inner bead): Too much heat or the gap is too wide. The puddle melts through and collapses inward instead of forming a reinforcement bead. Reduce amps, narrow the gap, or increase travel speed.

Wagon tracks (lines of slag along the root toes): The hot pass wasn’t hot enough to burn out root pass slag, or cleaning between passes was inadequate. Run the hot pass hotter (10-15 amps above root pass) and clean more aggressively.

Incomplete fusion in fill passes: Rod angle isn’t directing the arc into the sidewall. Angle the rod toward each bevel face as you work across the joint. Pause at the sidewalls. If you’re running stringer beads, each bead should overlap the bevel face by at least 1/8".

Undercut on the cap: Amperage too high, travel speed too fast at the toes, or arc too long. Reduce amps by 5, pause longer at each toe of the weave, and keep the arc tight.

Internal porosity on X-ray: Moisture in 7018 rods or contamination on the bevel faces. Check rod storage procedures. Clean the bevel faces with a grinder or solvent before welding. Also check for drafts that could disrupt shielding at the arc. See Stick Welding in Wind for outdoor considerations.

Pipe Welding Certification

Pipe welding certifications test your ability to make sound welds in specific positions:

• 2G: Pipe fixed vertical, welding horizontal. Simplest pipe position.
• 5G: Pipe fixed horizontal. You must weld around the full circumference without rotating the pipe. This is the standard structural pipe test.
• 6G: Pipe fixed at 45 degrees. The most demanding test because it combines flat, horizontal, vertical, and overhead positions in a single joint. A 6G certification typically qualifies you for all pipe positions.

Most certification tests use 6" schedule 80 pipe (0.432" wall). The joint is beveled at 37.5 degrees per side with a 1/16" root face and 3/32" root gap. Two test coupons are cut from the completed weld and subjected to guided bend tests (root bend and face bend). Any crack, lack of fusion, or porosity over 1/8" fails the test.

Practice with the same pipe size, schedule, and electrode procedure you’ll test on. There’s no substitute for repetition on the exact configuration.