An open root pass is the first bead laid into an unbacked pipe joint, fused to both bevel faces with no backing ring or consumable insert to catch a mistake. On the 6G qualification test, welders rotate that root through every clock position on a pipe fixed at a 45-degree angle, so root quality alone determines whether the coupon survives bend testing later.
E6010 remains the standard electrode for this pass on carbon steel pipe, chosen for its digging arc and forgiving behavior in an open gap. Every fill pass, including the hot pass that follows immediately after, and the cap welding techniques after it depend on a root free of suck back, incomplete fusion, or excess penetration.
Get the root wrong and no amount of skill on later passes recovers the joint.
What Is an Open Root Weld and Why Use E6010?
The open root pass is where a welder balances full penetration against a keyhole that can quickly get away from you. During 6G Pipe Welding, that tension is constant because the pipe is fixed at 45 degrees and the same root must hold through flat, vertical, and overhead travel while the welder changes body position.
What the open root actually is
An open root is an intentional gap left between the beveled pipe ends, usually with a small land or root face. There is no backing ring or insert behind the joint. The welder burns through that gap and fuses the inside edges of both bevels as the arc passes. The root opening, land, and bevel angle are set when you bevel pipe for welding, but the open root itself is simply that unsupported gap. The goal is a continuous root bead with 100 percent penetration and a uniform inside profile.
Why the 6G position raises the bar
In the 6G fixed position, the pipe does not rotate, so the welder moves through overhead, vertical, and flat segments in one pass. Any spot that lacks fusion, drops too much reinforcement, or leaves a wagon track on the inside becomes a failure point. Because the inside of the pipe is hard to reach, the root pass has to be right the first time. Inspectors often cut the coupon and look directly at the inside bead, so consistency matters as much as penetration.
Why E6010 is the standard choice
E6010 is a fast-freeze, cellulosic electrode. Its arc digs in for deep penetration, and the slag freezes quickly enough to hold the keyhole and support the puddle during a whip-and-pause motion. It runs on DC electrode positive only, which helps drive the arc into the root. The fast-freezing slag is also what lets a welder control the keyhole on vertical and overhead sections without the puddle falling through. That combination is why E6010 remains the go-to rod for open root stick welding on pipe.
This is step two in the 6G pipe test sequence, right after fit-up and tacking. The hot pass comes next.
Joint Preparation: Root Gap, Land, and Bevel Angle
What root gap, land, and bevel angle should you use for an open root E6010 pipe pass in Stick Welding?
A practical starting fit-up for a 6G carbon steel Welder Certification test coupon using 1/8 in. E6010 is a 1/8 in. (3.2 mm) root gap, a 3/32 in. (2.4 mm) land or root face, and a 30 degree bevel on each side, producing a 60 degree included angle. That combination gives the electrode enough room to keyhole through the back side while leaving enough metal behind the bevel to avoid blowing through.
How the dimensions fit the weld
With a 1/8 in. electrode, a 1/8 in. gap lets the arc push a controlled keyhole without forcing you to whip too far ahead. If the wall is thinner, tighten the gap slightly; on thicker wall, open it up a little, but stay within the WPS range. A land of about 3/32 in. protects the bottom edge from melting back too fast. A smaller land, around 1/16 in., makes the root easier to open but increases the chance of suck back or burn-through.
Code dimensions and common test practice
Do not treat these numbers as fixed for every job. AWS D1.1 fit-up tolerances are commonly ±1/16 in. for root opening and root face, and +10 degrees or -5 degrees for groove angle, but those apply only when the governing joint detail specifies the nominal. A prequalified open root joint may permit a root opening from 0 to 3/16 in.2, while many 6G carbon steel test coupons are set up with a 3/32 in. to 1/8 in. root gap and a 1/16 in. to 3/32 in. land3. Some test center WPSs and ASME Section IX preparation guides use a 37.5 degree bevel per side, or 75 degrees included4, instead of the 60 degree included starting point. Check the joint sketch and procedure before you grind.
Clean, square edges
Bevel faces need to be flat and square across the pipe wall. Remove mill scale, oil, rust, and moisture from the bevel, land, and the first inch inside and outside the pipe. Use a grinder or file to knock off burrs and then wipe the joint dry. Keep a gap gauge or a set of 1/8 in. filler rods handy to check the root opening at the 6 o'clock, 9 o'clock, 12 o'clock, and 3 o'clock positions so the gap stays consistent. A poorly cleaned or uneven fit-up will show up as lack of fusion, trapped slag, or an oversized keyhole in the root pass before you move to the hot pass.
Machine Settings and Electrode Choice for E6010
Start With the Right Polarity
Set the machine to DC electrode positive, or DCEP.1 E6010 will not run on AC, and trying to force it produces an unstable arc, heavy sticking, and poor root control. DCEP drives penetration into the open root and keeps the keyhole moving.
Dial In Amperage for the Root
For a 1/8-inch E6010 on a 6G open root, start around 83 amps. Treat 75 to 95 amps as the working window.2 The exact setting depends on root opening, land, wall thickness, travel speed, and position. If the gap is generous or the pipe wall is thin, or if the overhead and vertical puddle is too fluid, drop toward 75 to 80 amps. If the arc feels cold, the electrode sticks, or sidewall fusion is weak, move toward 90 to 95 amps. The Lincoln Electric Stick Electrode Catalog can show a broader 75 to 130 amp DC positive range, but a 6G root pass does not need the top of that range. For 3/32-inch E6010, use a lower amperage than the 1/8-inch setting and follow the electrode manufacturer's published range.
Travel Angle and Arc Force
Hold a 10 to 15 degree drag travel angle, keeping the electrode perpendicular to the pipe axis. That angled drag helps push the keyhole forward and deposit root metal. On an inverter, set arc force or dig to a moderate value, typically 20 to 40 percent of the available range.3 Moderate arc force reduces sticking without making the arc harsh. Increase it slightly if the electrode grabs during a tight keyhole or close arc. Decrease it if the arc becomes violent, the puddle washes out, or undercut appears at the edges. Keep hot start low to moderate as well; too much hot start can enlarge the arc strike and cause burn-through at the start of the bead.
Before You Strike an Arc
Confirm DCEP on the machine, begin near 83 amps for a 1/8-inch E6010, use a 10 to 15 degree drag angle, and set arc force modestly. Then adjust within the 75 to 95 amp window based on keyhole size, puddle control, and root fusion before moving to the hot pass.
Open Root Technique in the 6G Position
Keep the keyhole around 1/8 inch at the leading edge of the puddle.1 This small, controlled opening is the signal that the E6010 arc is fully penetrating the root without blowing through or bridging the gap.
Keyhole Control with Whip-and-Pause
Whip-and-pause is the standard root technique for most 6G E6010 tests. Move the electrode forward just ahead of the puddle, then whip back into the weld pool long enough to fill and freeze.
- Forward whip: Move the electrode just ahead of the puddle to open the keyhole.
- Back step: Return into the pool to deposit metal and let it freeze.
- Repeat: Keep each step about one electrode diameter2 and hold a short arc near 1/8 inch.1
A long arc widens the keyhole and makes the puddle harder to freeze.
Watch keyhole size before every whip. If the hole widens past about 1/8 inch, increase whip distance or speed.3 If the keyhole closes and the arc no longer pushes through, slow the travel slightly or make a shorter pause before continuing.3 A steady keyhole also prevents suck-back and cold lap on the inside of the pipe.
Travel Angle Around the 6G Ring
On the top flats, hold a 10 to 15 degree drag travel angle. That keeps the arc force pushing back into the root. Near the bottom, gravity wants to pull the puddle ahead, so stand the rod closer to perpendicular and let the whip sequence hold the keyhole. The same whip-and-pause rhythm works through flat, vertical, and overhead sections; angle changes are the main adjustment. For downhill roots, the same drag angle ranges from 10 to 20 degrees; the exact angle shifts with pipe diameter and fit-up.4
A straight drag can work on downhill or thin-wall pipe when the keyhole naturally stays centered and stable.5 If a school or contractor permits it, a drag root may be used when fit-up is tight and the keyhole stays small without whipping. But most 6G open root tests are run with whip-and-pause because it gives direct control of penetration.
Restarts and Tie-Ins
When a rod burns out, grind the stop into a thin feathered edge. Strike the arc slightly ahead of the crater,6 move back into the existing puddle, and let the keyhole re-establish before traveling forward again. Do not restart on top of a closed crater; the feathered edge lets the new pass melt into sound metal. Keep the arc short and continue the same rhythm across the tie-in so the new metal blends into the old root instead of sitting on top.1
At the segment ends, keep the same keyhole size and travel pace through the tie-in.1 Work until the segments meet cleanly around the bottom, including the 6 o'clock point, so the completed root pass has a consistent internal bead before the hot pass and cap weld.1
Related Articles
Troubleshooting Common Open Root Defects
Most open root E6010 failures can be traced to a single habit: the welder stops watching the keyhole as a shape and instead reacts to symptoms after the puddle has already changed. Fix the keyhole early and most root pass defects disappear before they harden into repair work.
Keyhole Too Large or Growing
When the keyhole opens wider than the electrode end, the weld bead can sag or burn through. First tighten the arc and steer the keyhole toward the bevels with a small oval motion. Increase travel speed slightly1; many welders make the mistake of dropping amperage before correcting the manipulation. If the keyhole keeps growing, reduce amperage in small increments when the qualified welding procedure specification (WPS) allows it, and if it becomes uncontrolled, stop and let the joint cool rather than trying to chase it. Changing root opening or land is a fit-up correction, not an in-the-moment fix, and should only be done if the joint is already outside the procedure.
Keyhole Closing or Too Tight
A closing keyhole usually means the arc is too long, travel speed is too fast, or whip dwell is too short. Shorten the arc, slow your forward progress2, and briefly hold the electrode on the land to reopen the keyhole before moving. Check that the gap and land match the WPS; if the root closes completely, stop and grind back about 1/4 inch into sound weld before restarting. Do not force an electrode into a collapsed keyhole because you will bury slag or produce a cold tie-in.
Suck-Back and Concave Root
Suck-back on the inside surface typically comes from traveling too fast, carrying too little filler, or a keyhole that is running too fluid. The correction is not automatically more amperage; excess heat can enlarge the keyhole and make the root worse. Slow your travel and use a tighter, slower whip or steady motion so the E6010 freezes in the bevels instead of falling through. If the puddle is too fluid even at a controlled speed, lower amperage slightly within the WPS range.
Lack of Fusion at Restarts
Restart defects usually come from trying to weld over a crater without removing the feathered oxidized edge. Grind the tie-in back to shiny metal, remove slag, and start 10 to 15 mm behind the previous crater2. Ride the new keyhole into the overlap, pause on the feathered edge so it fully fuses, and weld through at least 1/2 inch of sound root before continuing. If a restart is already defective, grind back to the original bevel, reopen the keyhole with a cutting wheel, and re-weld the short section cleanly before moving on to hot pass welding.
Inspection and Acceptance Criteria for the Root Pass
Under ASME B31.3 Table 341.3.2A, internal root protrusion is capped at 1/16 in. for pipe wall up to 6 mm thick, with separate values for heavier wall. That means the inspector is not just looking for a full-penetration bead; the inside convexity must also be uniform and within code limits. A pipe wall above 6 mm brings a different allowable number, so the applicable welding procedure specification remains the final authority.
Visual Acceptance Criteria for the Open Root
The root pass should show complete penetration along the full joint length with no unfused root face visible on the inside. Cracks, lack of fusion, incomplete penetration, and undercutting are rejected outright under ASME B31.3 Table 341.3.2A.1 Root concavity or suck-back is evaluated differently. It may be acceptable only when the total joint thickness, including weld reinforcement, still equals or exceeds the required base metal thickness.3 If the valley removes enough metal to fall below that required thickness, the root is rejectable. On small pipe, a concavity deeper than about 1/16 in. is a practical warning sign, but the governing test is remaining wall thickness, not the visual depth alone. The common shop rule that internal convexity must stay under 1/8 in. is not universal; ASME B31.3 uses 1/16 in. for thin-wall pipe.
Guided Bend Testing of the Root Pass
Guided bend testing is the most direct way to see whether the root has fused. The root bend places the root side in tension. Because the weld's root is on the outside of the bend, lack of fusion, incomplete penetration, root cracking, and root suck back open under strain if they are present. A face bend tests the opposite orientation, exposing the cap or face side, while a side bend pulls the full cross section through the thickness. The specimen passes when the bent surface shows no unacceptable open defects. For qualification under applicable codes, the weld must usually bend to the same angle as the base metal, within a narrow tolerance, without opening a crack or other defect beyond the code's limit.
What Codes Reject
API 1104 treats cracks, lack of fusion, and incomplete penetration as rejectable when found by radiographic or other applicable examination.3 Under ASME B31.3, these conditions are not allowed by size adjustment in the root pass.1 Excess concavity, burn through, and incomplete root fusion all point to the same practical conclusion: the root pass has not maintained a sound, full-thickness joint.3 Inspect the inside of the pipe, note any area that appears sucked back or flat, and chase it with the next pass only after the defect is evaluated against the WPS.
NIOSH research shows welders face a roughly 40 percent higher relative risk of lung cancer compared to non-welders, even before factoring in cigarette use. Open root passes generate especially fine fume near your breathing zone, so proper ventilation and a well-fitted respirator aren't optional extras, they're essential gear every time you strike an arc.
By 1964, Lincoln Electric's catalog already recommended Fleetweld 5P (E6010) for the root pass on high-pressure pipelines, pairing it with low-hydrogen electrodes for fill and cap passes. That means the stovepipe technique welders still practice today for the 6G test was standard pipeline procedure over 60 years ago.
Frequently Asked Questions About Open Root E6010 Welding
- What is the proper root gap and land size for open root pipe welding?
- There is no universal size. Common practice is 1/16 to 1/8 inch for both root gap and land, but the WPS, wall thickness, bevel, and code control final dimensions. Some 6G test setups use a 1/8 inch gap plus or minus 1/32 inch and a 3/32 inch land plus or minus 1/32 inch.2
- How do you control the keyhole when welding an open root with E6010?
- Use a short, tight arc and keep the electrode tip in the root opening, not on the bevel faces. Maintain a controlled whip and pause with a small keyhole around 2 to 3 mm.1 If the keyhole grows, travel faster or shorten the arc; if it closes, slow travel and push the rod.
- What causes suck back in an open root weld?
- Suck back is an excessively concave root surface from molten metal being withdrawn. Excessive heat or amperage, high travel speed, a wide gap or thin land, poor fit-up, long arc length, wrong electrode angle, a poorly filled restart, or poor 6G puddle control can cause it.
- How do you restart an open root pass without lack of fusion?
- Stop in a controlled way, slow the final 10 to 15 mm, and leave a small mound. Grind the crater and last 15 to 20 mm of weld. Start the new electrode on sound metal 10 to 15 mm behind the stop, travel into the crater, and pause until the puddle reflows and the keyhole returns.
- What is the difference between a root pass and a hot pass?
- The root pass bridges the opening and establishes root fusion, penetration, and internal profile. The hot pass follows immediately, usually with higher heat, to fuse and clean the root surface and support fill passes. Its amperage, electrode size, and timing must be WPS qualified.
- How do you inspect an open root weld for the 6G test?
- After cleaning, inspect the root face and inside of the pipe where accessible. Look for excessive root penetration, suck back, lack of fusion, and a uniform root profile, especially at stops and restarts. Acceptance criteria come from the code, test standard, and WPS.