6G Pipe Welding Test Tips: How to Pass Your Certification

Q: "How long does it take to learn 6G pipe welding?"

"Most welders need 3-6 months of focused practice after they're already competent in flat and vertical plate welding. That's practicing pipe at least 4-5 hours a day, 5 days a week. Some pick it up faster, but rushing into a test before you're ready just wastes money on test fees and coupons. Cut your practice welds open and check the root before you schedule a test."

Q: "What happens if I fail a 6G test?"

"You can retest, usually after a waiting period (24 hours to 30 days depending on the testing facility). Most facilities let you retest on the spot if you have additional test coupons. The failure is documented, but it doesn't follow you permanently. Many excellent pipe welders failed their first 6G attempt. The key is understanding why you failed and fixing it before retesting."

Q: "What electrodes are used for a 6G pipe test?"

"The most common combination is TIG (GTAW) root with ER70S-2 or ER70S-6 filler wire, then SMAW (stick) fill and cap with E7018. Some tests allow all-TIG or all-stick. E6010 root with E7018 fill and cap is the traditional stick-only combination. Your WPS specifies exactly which consumables are allowed."

Published August 15, 2025 · Updated March 17, 2026 · 8 min read

Passing a 6G pipe test comes down to three things: a clean root pass, consistent fill passes, and a smooth cap. The test puts a pipe coupon at 45 degrees and makes you weld every position in one joint. Most failures happen at the root, specifically in the overhead-to-vertical transition zone around 5-7 o’clock. Prepare for that section and you’ll pass.

The 6G test is the gold standard for pipe welders. One passing test qualifies you for all pipe and plate positions on the process and thickness range covered by the WPS. It’s the most demanding single certification in the trade, and it’s what contractors look for when hiring.

Test Setup

Coupon Preparation

Standard test coupon: two pieces of 6-inch or 8-inch schedule 80 carbon steel pipe (A106 Grade B), each about 6 inches long. The joint preparation is:

Bevel: 37.5 degrees per side (75 degrees included)
Root face (land): 1/16 to 3/32 inch
Root opening (gap): 3/32 to 1/8 inch

Critical: Consistent root opening around the entire circumference. Spend time on fit-up. If your gap varies by more than 1/32 inch, you’ll fight the root pass.

Tack Welds

Place four tack welds at 12, 3, 6, and 9 o’clock. Keep tacks about 1/2 inch long and grind or feather the starts and stops so they blend into the bevel. A lump from an unground tack disrupts the root pass and creates a potential lack-of-fusion defect.

Some welders use three tacks (120 degrees apart) instead of four. Fewer tacks mean fewer disruptions to the root pass, but the gap must be perfectly consistent.

Coupon Positioning

The pipe sits at 45 degrees from horizontal. Make sure it’s rigidly clamped. Any movement during welding changes the puddle behavior and creates inconsistency.

Mark your quadrants on the pipe with a soapstone. This helps you track where you are during the weld, which matters for adjusting technique at the transitions.

Root Pass Strategy

The root pass makes or breaks the test. Inspectors look at root penetration first, and most failures trace back to this pass.

TIG Root (Preferred Method)

TIG with ER70S-2 or ER70S-6 filler wire on DCEN:

Amperage: Start at 75-90 amps on 1/8 inch tungsten (adjust for the specific machine and coupon)
Gas: 100% argon at 15-20 CFH
Filler: 1/16 or 3/32 inch ER70S-2/S-6

Keyhole technique: Maintain a small opening (keyhole) at the leading edge of the puddle. The keyhole guarantees full penetration. If the keyhole closes, increase amperage slightly or slow down. If it grows too large, add filler faster and reduce amperage.

Starting at 6 o’clock: You’re overhead with an uphill angle. This is the hardest section. Keep the arc tight, amperage at the lower end, and feed filler consistently. The keyhole should be tiny here since gravity wants to pull the puddle through.

Transition through 3-9 o’clock: Vertical work. Slightly increase amperage as you leave the overhead zone. The keyhole becomes easier to control. Pause slightly at each side of the keyhole to fill the toes.

Approaching 12 o’clock: Near-flat. Increase travel speed to prevent excessive root reinforcement. The puddle wants to stay in place here, so it’s easy to overweld.

Tie-in: Where the bead meets itself at 12 o’clock (or wherever you started), feather the existing bead by grinding a slight taper and weld over it. The tie-in should be invisible.

Stick Root (E6010)

For stick-only procedures:

E6010, 1/8 inch diameter, DCEP
Amperage: 75-90 amps
Whip and pause: Advance 1/8 inch, pause to fill the keyhole, whip forward. The rhythm is critical.
Same position strategy as TIG: lower heat overhead, more at the top

The E6010 root is less forgiving than TIG. The puddle is harder to see through the slag, and the keyhole is harder to control. But it’s faster, and many pipeline jobs still require it.

Root Pass Acceptance Criteria

Internal (root) reinforcement: 1/32 to 1/8 inch
No melt-through or icicles hanging inside the pipe
No lack of penetration (flat or concave root surface)
No porosity visible on the root surface
Smooth, uniform appearance on both internal and external surfaces

Hot Pass

The hot pass immediately follows the root, while it’s still warm. It accomplishes two things: burns out any contamination at the root toes and builds a solid foundation for fill passes.

Timing: Start within a few minutes of finishing the root. The joint should still be warm to the touch.
Electrode: Switch to E7018 (SMAW) for a TIG-root/stick-fill procedure. E7018 on DCEP, amperage slightly higher than the root pass (typically 95-115 amps for 3/32 inch rod).
Technique: Slight weave (1/8 inch side to side) to wash into both root toes. Move steadily. The goal is fusion into the root toes, not a big bead.
Cleaning: Wire-brush the root before the hot pass. Chip and brush the hot pass before fill.

Fill Passes

Fill passes build the groove up to within 1/16 to 1/8 inch of the pipe surface. Run stringer beads, each overlapping the previous pass by about 50%.

Key Points

Stringer beads, not wide weaves. Wide weaves trap slag at the toes in positional work.
Electrode angle: Direct each bead into the bevel face to ensure sidewall fusion.
Interpass cleaning: Chip all slag completely between every pass. Slag inclusions are a common NDE rejection.
Interpass temperature: Keep it under 600F for carbon steel. Use a contact thermometer, not your hand.
Bead placement order: Start each fill layer along the bottom bevel face, then stack beads across the groove.

Pass Count

On 6-inch schedule 80 (0.432 inch wall):

Root: 1 pass
Hot pass: 1 pass
Fill: 3-5 passes depending on bead size
Cap: 1-2 passes

Total: 6-9 passes. Don’t rush by running fat fill passes. Thinner, consistent beads are easier to control in position and produce fewer defects.

Cap Pass

The cap is the visible finish. It’s what the inspector examines first.

Acceptance Criteria

Width: extends 1/16 to 1/8 inch beyond each bevel edge
Height: slightly convex, no more than 1/8 inch above the pipe surface (per AWS D1.1) or 1/16 inch (per ASME)
Surface: uniform ripple pattern, no undercut, no porosity
Consistent width and profile all the way around the pipe

Technique

Use E7018 at comfortable amperage (100-120 amps for 1/8 inch rod, depending on position)
Slight weave, pausing at each toe
Overhead section: tighter weave, lower heat, faster travel
Flat section: slower, wider weave to fill without building up too high

Common Failures and How to Avoid Them

Failure Mode	Location	Cause	Prevention
Lack of root penetration	6-8 o'clock (overhead)	Insufficient heat, fast travel, gap closure	Consistent gap, keyhole technique, proper amperage
Root concavity (suck-back)	12 o'clock area	Too much heat, too thin a root face	Reduce heat at top, proper land dimension
Excessive root reinforcement	12 o'clock area	Too slow, too much filler, keyhole too large	Increase travel speed, control filler addition
Slag inclusion	Fill passes, any location	Incomplete slag removal between passes	Chip and brush every pass completely
Undercut	Cap toes, horizontal section	Excess heat, fast travel, wrong angle	Pause at toes, reduce amperage, watch the toe fusion
Porosity	Root or cap	Contamination, wet rods, wind (TIG)	Clean joint, proper rod storage, wind screens

Practice Schedule

A realistic 6-week preparation plan for a welder who’s already competent on plate:

Weeks 1-2: Root passes only. Cut open every practice coupon and inspect the internal root. Don’t move to fill passes until your roots are consistently clean with proper penetration.

Weeks 3-4: Full welds (root through cap). Focus on the overhead-to-vertical transition. Time your welds. You should complete a root pass in about 20-25 minutes on a 6-inch pipe.

Weeks 5-6: Timed practice tests. Set up the coupon exactly like the test. Complete the entire weld under test conditions. Cut one coupon per week and bend-test it if you have access to a guided bend fixture.

Material budget: Plan for 15-25 practice coupons. At about $20-30 per coupon (two pieces of schedule 80 pipe), that’s $300-750 in material.

What Inspectors Look For

Root penetration: Consistent internal reinforcement, no lack of penetration
Root profile: Smooth, no wagon tracks, no icicles
Cap profile: Uniform width and height, smooth tie-in at toes
Undercut: None visible, or within tolerance (typically 1/32 inch max)
Porosity: None visible on surface
Start/stop quality: Clean tie-ins with no craters or overlap defects
Overall appearance: Consistent around the entire circumference

After visual, the coupon gets sectioned into bend specimens (face bends and root bends). Any open defect over 1/8 inch on a bent specimen is a failure.

Common Mistakes

Testing before you’re ready. If your practice roots aren’t consistent, you’re not ready. The pressure of a test doesn’t magically improve your technique.

Not practicing in the actual test position. Practice on the bench in 5G doesn’t prepare you for 6G. Set up the coupon at 45 degrees every time.

Ignoring tie-ins. The spots where beads start and stop are defect-prone. Practice tying in cleanly by grinding a taper on the existing bead and welding over it smoothly.

Using different equipment for practice and test. If the testing facility has a different brand of TIG machine or a different style electrode holder, get comfortable with it before the test.

For more on pipe positions, see the pipe welding positions guide. For the multi-pass sequence in detail, read root pass, hot pass, fill, and cap. Return to pipe welding or the welding techniques pillar for more resources.

Frequently Asked Questions

How long does it take to learn 6G pipe welding?

Most welders need 3-6 months of focused practice after they're already competent in flat and vertical plate welding. That's practicing pipe at least 4-5 hours a day, 5 days a week. Some pick it up faster, but rushing into a test before you're ready just wastes money on test fees and coupons. Cut your practice welds open and check the root before you schedule a test.

What happens if I fail a 6G test?

You can retest, usually after a waiting period (24 hours to 30 days depending on the testing facility). Most facilities let you retest on the spot if you have additional test coupons. The failure is documented, but it doesn't follow you permanently. Many excellent pipe welders failed their first 6G attempt. The key is understanding why you failed and fixing it before retesting.

What electrodes are used for a 6G pipe test?

The most common combination is TIG (GTAW) root with ER70S-2 or ER70S-6 filler wire, then SMAW (stick) fill and cap with E7018. Some tests allow all-TIG or all-stick. E6010 root with E7018 fill and cap is the traditional stick-only combination. Your WPS specifies exactly which consumables are allowed.