Tack Welding Best Practices: Placement, Size, and AWS D1.1 Requirements

Tack welds hold the joint in position for production welding. They control root opening, alignment, and fit-up during the thermal stresses that follow. A tack weld that’s too small cracks under shrinkage. One that’s too large resists re-melting and creates a bump in the production weld. Getting tack placement, size, and quality right prevents rework on every joint you weld.

AWS D1.1 treats tack welds that stay in the joint as production welds. That means same process, same consumable, same quality standard. A cracked tack welded over becomes a crack buried in the production weld. There’s no shortcut here.

Tack Weld Placement

Spacing Guidelines by Material Thickness

Tacks need to be close enough to hold the root opening and alignment consistent, but far enough apart that they don’t overly restrain the joint.

Thin material needs closer tack spacing because it’s less rigid and more likely to shift during welding. Pipe tacks are generally closer together than plate tacks because the curved geometry makes misalignment more likely.

Placement Strategy

On a butt joint: Place the first tacks at each end of the joint, then fill in the middle. For long joints, work from the center outward to maintain uniform gap:

1. Center tack first
2. Quarter-point tacks (1/4 and 3/4 of the joint length)
3. Fill in remaining gaps as needed

Don’t tack from one end to the other sequentially. This allows the gap to close or open as you move along, and by the time you reach the far end, the fit-up may be off.

On pipe: Standard four-tack placement at 12, 3, 6, and 9 o’clock positions. Three tacks at 120-degree intervals also work and leave fewer disruptions for the root pass.

On tee joints: Tack on one side only if the fillet welds will be on both sides. This keeps the other side clean for the first production pass. If both sides need tacking, stagger the tacks so they don’t oppose each other.

At corners and intersections: Place tacks at the corners first to establish the geometry, then fill in along the straight sections.

Tack Weld Size

Length

Tack weld length depends on the joint and the forces the tack must resist:

Longer tacks provide more holding strength but are harder to re-melt during the production weld. Keep tacks as short as practical while still holding the joint.

Cross-Section

The tack weld cross-section should approximate the root pass cross-section. On a groove weld, the tack should fill the root opening and fuse into both root faces. On a fillet weld, the tack should match the first-pass leg size.

Throat

A tack with too small a throat cracks under shrinkage stress. The throat must be sufficient to resist the contraction forces that develop during production welding. A cracked tack is worse than no tack because it creates a defect that gets buried.

Tack Weld Quality

AWS D1.1 Requirements

AWS D1.1 Section 5.17 states:

• Tack welds incorporated into the final weld must be made with the qualified WPS
• They must be made by qualified welders
• Tacks must be cleaned of slag before the production weld
• Cracked tacks must be removed
• Tack starts and stops must be ground or feathered to blend into the groove

Quality Standards for Tack Welds

Same as production welds means:

• No cracks of any kind
• No porosity
• No slag inclusions
• Complete fusion into both base metal surfaces
• Proper profile (not excessively convex or undercut)

Process and consumable matching: If the production weld uses E7018, the tacks should use E7018 (or at minimum, a compatible electrode). Using E6013 to tack a joint that’ll be welded with E7018 introduces a different filler chemistry into the root.

For TIG-root pipe procedures, tacks should be made with TIG using the same filler wire. Stick-tacking a TIG-root joint forces the root pass to re-melt a different deposit type.

Incorporation vs. Removal

Tacks Incorporated into the Final Weld

Most tacks on structural steel and pipe are left in place and consumed by the production weld. The production pass melts through the tack and incorporates the tack metal into the weld.

Requirements for incorporation:

• Tack made with the same process and consumable as the production weld
• No cracks or defects in the tack
• Starts and stops feathered (ground to a taper so the production weld transitions smoothly over them)
• Slag completely removed

Feathering Tack Welds

Feathering means grinding the start and stop of each tack to a thin taper. This prevents a bump that the production weld has to melt through. An unfeathered tack creates a thick spot where the root pass rides over it instead of re-melting it, causing lack of fusion.

How to feather:

• Use a small grinding disc (4-1/2 inch angle grinder with a thin grinding wheel)
• Grind the start and stop of each tack to a gradual taper over 1/4 to 1/2 inch
• The tack should blend smoothly into the bevel
• Don’t grind into the base metal beside the tack

Tacks That Must Be Removed

Remove tack welds when:

• The tack is cracked
• The tack was made with an incompatible process or consumable
• The tack is on the back side of a joint that requires back-gouging
• The drawing or WPS specifies tack removal
• The tack is in a location where it’ll interfere with the production weld sequence

Removal method: Grind the tack completely flush with the base metal. Verify no residual weld metal remains in the groove. On critical applications, PT or MT the ground area to confirm no cracks.

Tack Weld Sequence for Distortion Control

Tack sequence affects initial distortion before production welding even starts.

Center-Out Method

Start at the center of the joint and work outward toward both ends:

1. Center tack (establishes the midpoint gap)
2. Tack at 1/4 point (left of center)
3. Tack at 3/4 point (right of center)
4. Tack at left end
5. Tack at right end
6. Fill in remaining gaps

This holds the center gap constant while allowing the ends to adjust. Each tack locks a portion of the gap, and working outward lets the remaining free length accommodate any minor misalignment.

Alternating Method

Alternate tacks between opposite ends:

1. Left end tack
2. Right end tack
3. Center tack
4. Between center and left
5. Between center and right

This prevents gap closure from progressing in one direction.

Pipe Tack Sequence

On pipe, place opposing tacks first:

1. 12 o’clock
2. 6 o’clock (opposite)
3. 3 o’clock
4. 9 o’clock (opposite)

This holds the pipe round and maintains gap consistency around the circumference.

Tack Welding Thin Material

Thin material (under 1/8 inch) presents special challenges:

• Burn-through risk: Use lower amperage and shorter tack duration
• Distortion from tacks: Even small tacks distort thin sheet. Use the minimum number of tacks needed, and consider clamps or fixtures as alternatives
• Tack cracking: Thin material cools fast, which can crack tacks. Preheat helps if the material is crack-sensitive
• MIG tack technique: Use a spot weld timer function if your machine has one. Set a short weld time (0.5-1.0 seconds) for consistent, controlled tacks.

Common Mistakes

Tacking with whatever electrode is in the stinger. If the production weld uses E7018, tack with E7018. Using E6013 because it’s already loaded introduces a different filler chemistry that gets incorporated into the production weld.

Not feathering tacks on pipe. Unground tack ends create humps in the root pass. The root bead rides over the hump instead of fusing through it, creating lack of fusion. Feather every tack on pipe.

Cracked tacks left in place. A cracked tack is a defect. It gets buried by the production weld but doesn’t heal. Grind it out, determine why it cracked (too small, wrong electrode, too much restraint), fix the cause, and re-tack.

Tacking from one end to the other. Sequential tacking lets the gap change as you progress. The far end may have a different root opening than the near end. Start at the center and work outward.

Over-tacking. Too many tacks make the joint excessively rigid. This increases restraint on the production weld, which can cause cracking in sensitive materials. Use the minimum number of tacks that holds the joint.

Tacking on the wrong side of a fillet joint. If both sides get welded, tack on the side that gets welded first. Tacks on the second side go under the production weld without being consumed by the first-side weld, potentially creating a defect.

For fit-up tolerances that tack welds must maintain, see the fit-up tolerance guide. For distortion control through welding sequence, see the weld sequence for distortion control and the back-stepping technique guides. Return to preheat and post-weld or the welding techniques pillar for more resources.