3G Plate Test Guide: Vertical Welding Certification Step by Step

The 3G vertical plate test is the foundation of structural welding certification. It qualifies you for flat, horizontal, and vertical positions on plate. Pair it with a 4G (overhead) test and you’re qualified for all positions, which is the minimum most structural shops require for new hires.

The test uses a standard 3/8 inch plate, single-V groove joint, welded in the vertical-up position. You’ll run a root pass, fill passes, and a cap. The coupon gets visually inspected and then destructively tested with guided bend tests. Pass rate for prepared welders is high. Pass rate for unprepared welders is not.

Test Plate Setup

Plate Dimensions

Standard 3G test plate dimensions per AWS D1.1:

• Plate thickness: 3/8 inch (10 mm)
• Plate width: 7 inches (178 mm) minimum, two pieces
• Plate length: Typically 7 to 10 inches
• Material: A36 carbon steel or equivalent

Joint Design

The standard single-V groove joint for a 3G test:

With backing strip: A 1/4 inch thick, 1 inch wide steel strip is tacked to the back of the joint. The root opening is 1/4 inch. This is the more forgiving configuration because the backing strip catches the puddle and prevents burn-through.

Open root (without backing): The root opening is 1/8 inch with a 1/8 inch root face. You need controlled penetration through the joint with no blow-through. This is the harder test and qualifies you for open-root production work.

Tacking the Test Plate

Tack the two plates together with the correct root opening. Use tacks at each end and one in the middle if needed for a long plate. Tacks should be small (1/2 to 3/4 inch long) and made with the same electrode you’ll use for the root pass.

Critical: Verify the root opening is consistent along the entire joint length. A root that’s 1/4 inch at the top and 3/16 inch at the bottom will cause problems. Use a spacer (a piece of 1/4 inch plate for backing strip tests, a 1/8 inch electrode for open root) to maintain consistent gap.

Position the test plate vertically with the weld axis running straight up and down. The joint should be at a comfortable working height, roughly chest to chin level.

Root Pass Technique

The root pass makes or breaks the test. Get a sound root and the rest is straightforward.

Root Pass with Backing Strip

• Electrode: E7018, 3/32 inch diameter
• Amperage: 75-90 amps (adjust to plate and conditions)
• Technique: Slight weave, triangular motion, or side-to-side oscillation
• Travel: Uphill (bottom to top)
• Arc length: Tight, 1/8 inch or less (drag the coating)

Start at the bottom of the joint. Strike the arc on the backing strip in the root area. Establish a puddle, then begin traveling uphill. The goal is full fusion to both bevel faces and the backing strip.

Watch the puddle. You should see it wash into each sidewall and spread across the backing strip. If you see a dark line where the puddle meets the bevel, you’re not getting fusion. Increase amperage slightly or slow your travel.

Use a slight weave pattern. On each sidewall, pause briefly to allow the puddle to wash in, then move to the opposite side. Don’t weave too wide; keep it within the root area. The deposited bead should fill the root completely without excessive buildup.

Root Pass Open Root

• Electrode: E6010 (3/32 inch) or E7018 (3/32 inch) per the WPS
• Amperage: E6010 at 65-80 amps, E7018 at 70-85 amps
• Technique: Whip and pause (E6010) or straight drag (E7018)
• Travel: Uphill

For E6010 open root, use the whip-and-pause technique. Push the electrode into the joint to establish a keyhole, then whip forward about 1/4 inch and pause. The keyhole should be visible at the leading edge of the puddle, about the diameter of the electrode core wire. Whip forward to control heat, pause to let the puddle fill in.

For E7018 open root, use a drag technique with tight arc length. Keep the electrode pushed into the joint and travel steadily uphill. E7018 doesn’t form a keyhole as clearly as E6010, so you’re watching the puddle for consistent width and fusion.

The keyhole tells you everything. If it’s too big, you’re putting in too much heat (blow-through risk). If it closes up, you’re losing penetration. Consistent keyhole size equals consistent root penetration.

Fill Passes

After the root, grind or chip all slag and visually inspect the root pass. Look for:

• Consistent root penetration (visible on the back side if you can check)
• No cracks
• No slag trapped at the toes
• Profile is flat to slightly convex

Fill Pass Parameters

• Electrode: E7018, 1/8 inch diameter
• Amperage: 110-130 amps (adjust for position and buildup)
• Technique: Slight weave, stringer beads, or combination

Vertical Up Fill Technique

The standard vertical-up fill technique for 3G testing:

1. Start at the bottom of the joint on top of the root pass
2. Use a slight weave (1/2 to 3/4 inch wide). Pause at each sidewall for about half a second to allow the puddle to wet in
3. Build a shelf. In vertical welding, you’re building each pass on a shelf of solidified metal below. The puddle follows gravity, so you’re always working on the leading edge
4. Keep the arc on the leading edge. Don’t bury the arc in the puddle. Stay at the front where the bead meets the base metal
5. Watch the toes. Each pass should fuse completely into both sidewalls and the previous pass

Number of Fill Passes

On 3/8 inch plate, you’ll typically need:

• Root pass (1 pass)
• Fill passes (2 to 3 passes, depending on technique)
• Cap pass (1 pass)

Total: 4 to 5 passes. Don’t overbuild. Fill the joint to within 1/16 to 1/8 inch of the plate surface, then cap.

Common Fill Pass Problems

Undercut on sidewalls: Too much heat or dwelling too long. Reduce amperage by 5 amps or speed up slightly at the sidewall.

Cold lap between passes: Not enough heat or wrong work angle. The arc needs to be directed at the junction between the previous pass and the sidewall, not just riding on top.

Wagon tracks (valley in the center): The weave pattern is too wide. The center of each pass cools and solidifies before the arc returns, creating a valley. Narrow your weave.

Cap Pass

The cap is the final pass and what the inspector sees first. Plan it before you start.

Cap Pass Technique

• Electrode: E7018, 1/8 inch diameter
• Amperage: Same as fill or 5 amps lower to reduce undercut risk
• Technique: Weave width slightly wider than the groove (1/16 to 1/8 inch overlap past the bevel edge on each side)

The cap should be slightly convex, with uniform width and consistent ripple spacing. Reinforcement should be 1/16 to 1/8 inch above the plate surface.

On a 3/8 inch plate with a 45-degree groove, the cap width is approximately 5/8 to 3/4 inch. A single weave pass typically covers this. If your groove is wider, you may need two stringer beads for the cap.

Toe fusion is critical. The cap must tie into the base metal without undercut. Pause at each sidewall transition to allow the puddle to wash out to the plate surface. If you see undercut forming, reduce your amperage by 5 amps.

What the Inspector Looks For

After you finish, the inspector examines your coupon. Here’s what they’re checking:

Visual Inspection

• Cracks: Zero tolerance. Any crack, anywhere, is a failure
• Porosity: Scattered surface porosity within limits may pass; clustered porosity is a problem
• Undercut: 1/32 inch max depth per AWS D1.1
• Reinforcement: 1/8 inch max above plate surface
• Weld width: Consistent, with slight overlap past the bevel edge
• Profile: Slightly convex, smooth transition at toes
• Arc strikes: None on the base metal outside the weld zone
• Starts and stops: Blended smooth, craters filled

Bend Tests

The inspector cuts bend test specimens from your coupon. For 3/8 inch plate:

Each specimen is bent 180 degrees around a mandrel. The convex surface is examined for:

• No crack or opening exceeding 1/8 inch in any dimension
• No incomplete fusion visible on the bent surface
• No slag inclusion visible on the bent surface

Root bend specimens are the ones that catch most failures. If your root pass has incomplete fusion or trapped slag, the root bend will open it up and make it visible.

Practice Routine

Here’s a proven practice schedule for passing the 3G:

Week 1-2: Root Pass Focus

• Weld 2-3 root passes per day on practice plates set up identically to the test
• Cut cross-sections and examine root fusion
• Adjust parameters until roots are consistently sound
• If using open root, practice until your keyhole control is automatic

Week 3: Fill and Cap

• Weld complete joints (root through cap) every session
• Focus on consistent fill pass technique and sidewall fusion
• Practice cap passes until width and profile are uniform
• Cut bend specimens from practice coupons and bend them

Week 4: Full Test Simulation

• Set up test plates exactly as they’ll be for the test
• Weld them under test conditions (no coaching, no extra time)
• Cut and bend every practice coupon
• Track your pass rate. If you’re passing 9 out of 10 practice coupons, you’re ready

How Many Practice Coupons?

Most welders need 10 to 20 complete practice coupons to feel confident for a 3G test. That’s roughly 20 to 40 pounds of 7018 electrode and 40 pieces of 3/8 inch plate. The material cost is $50 to $100, which is cheap compared to failing and retesting.

Day of Test Checklist

1. Verify the machine settings with a quick practice bead on scrap
2. Set up the test plate, check root opening with a taper gauge
3. Tack the backing strip (if used) and verify alignment
4. Weld the root pass. Stop and inspect it before continuing
5. Clean thoroughly between every pass. No exceptions
6. Build fill passes to the correct height
7. Weld the cap with consistent width and reinforcement
8. Fill your crater at the stop
9. Clean the finished weld and visually inspect it yourself
10. Hand it to the inspector with confidence

The 3G is a fundamental test that every structural welder should be able to pass consistently. It requires good root technique, patience with slag removal, and a steady hand on vertical-up welding. Practice the exact setup, inspect your own work critically, and the test becomes routine.