What is the maximum convexity allowed on a fillet weld under AWS D1.1?

AWS D1.1:2025 limits fillet weld face convexity to 1/16 in (2 mm) plus 7% of the specified leg size. For a 5/16 in fillet, the maximum convexity above the theoretical face is roughly 1/16 in + 0.022 in ≈ 0.084 in (about 2.1 mm). Convexity in excess of this threshold acts as a stress concentrator and must be corrected.

Can a groove weld have too much reinforcement and still pass?

Reinforcement height above the base-metal surface is limited — typically 1/8 in (3 mm) for welds on material up to 1 in thick, and 5/32 in (4 mm) for thicker plate, per AWS D1.1 visual acceptance requirements. Excessive reinforcement is a defect because the abrupt transition at the weld toes concentrates stress. It must be ground flush or within tolerance before acceptance.

What does 'underfill' mean on a groove weld and is it always a rejection?

Underfill (also called concavity or insufficient reinforcement) means the weld face surface lies below the plane of the adjacent base metal. AWS D1.1 does not permit underfill on groove welds — the weld must be flush or have positive reinforcement within the specified limit. Underfill must be corrected by adding weld metal before the joint is accepted.

Does the root side of a CJP groove weld have its own profile limit?

Yes. The root pass on the far side of a CJP groove weld, when visible or inspectable, is also subject to visual acceptance. Melt-through (burn-through) beyond 1/8 in is typically rejectable. Root concavity is allowed in limited amounts on welds made from one side with backing, per specific AWS D1.1 acceptance provisions for backing conditions.

Weld Profile Acceptance: Convexity, Concavity, and Reinforcement Limits

AWS D1.1:2025 sets explicit dimensional limits on fillet weld convexity, groove weld reinforcement, and underfill. Here is what CWIs measure and why profile matters.

Weld profile — the shape of the deposited bead relative to the base metal — is one of the first things a CWI measures during visual examination. Yet profile defects are among the most commonly missed discrepancies in field acceptance, particularly on fillet welds, where gauge reading is quick and often treated as a formality.

AWS D1.1:2025 is explicit: convexity, reinforcement height, concavity, and toe geometry all have dimensional limits. Exceeding any of them is a rejectable condition regardless of whether the joint achieved full fusion and the required throat.

Why profile matters structurally

A weld bead that is too convex or has a sharply undercut toe creates a stress concentration exactly where the fatigue crack wants to start — at the toe. Research backing AWS D1.1's profile limits shows that convex fillet welds with abrupt transitions exhibit fatigue lives significantly shorter than flat or slightly concave profiles. The same logic applies to groove weld reinforcement: a crown that is high and narrow concentrates stress at its edges under cyclic loading.

For statically loaded structures the risk is somewhat lower, but even static joints must pass profile inspection because gross convexity can indicate trapped slag, poor fusion, or a process that was running cold. Profile is a proxy for process control.

Fillet weld face convexity limits

AWS D1.1:2025 defines the maximum face convexity on a fillet weld as:

C ≤ 1/16 in (2 mm) + 0.07 × w

where w is the specified weld leg size.

For common leg sizes, this works out to:

Specified leg (w)	Max convexity (C)
3/16 in (5 mm)	0.073 in (1.9 mm)
1/4 in (6 mm)	0.0775 in (2.0 mm)
5/16 in (8 mm)	0.0838 in (2.1 mm)
3/8 in (10 mm)	0.0888 in (2.3 mm)
1/2 in (13 mm)	0.0975 in (2.5 mm)
5/8 in (16 mm)	0.104 in (2.6 mm)

In practice, 1/16 in is the dominant term on smaller welds. Experienced CWIs carry a convexity gauge specifically for fillet welds. Weld profile gauges (Hi-Lo, bridge cam, fillet weld gauge sets) that include a convexity step are the standard measurement tool.

Convex fillet welds usually result from:

Travel speed that is too slow, allowing the weld pool to pile up
Voltage that is too low relative to wire feed speed, creating a stiff arc
Wrong contact-to-work distance causing the arc to go short
Incorrect torch angle directing too much heat away from the base metal

Correcting excessive convexity requires mechanical grinding to restore the profile. Re-welding on top of a convex bead typically makes it worse.

Groove weld reinforcement limits

On a complete joint penetration (CJP) groove weld, the face side deposit must be flush with or slightly above the base-metal surface. AWS D1.1:2025 visual acceptance for groove weld reinforcement:

Material thickness up to 3/4 in (19 mm): reinforcement ≤ 1/8 in (3 mm) above the base metal surface
Material thickness > 3/4 in (19 mm) to 4 in (100 mm): reinforcement ≤ 3/16 in (5 mm) above
Material thickness > 4 in (100 mm): reinforcement ≤ 1/4 in (6 mm) above

These limits apply to the highest point of the weld face — not an average. Measure with a weld gauge placed across the base metal on both sides of the joint.

Transitions from the weld cap to the base metal must also be smooth — an abrupt, shelf-like edge at the weld toe is itself a defect even if the height is within tolerance. AWS D1.1 requires the toe transition to blend without sharp notches.

Excessive reinforcement almost always means the welder held the torch in place too long, travel speed was too slow, or the final cover pass used too much fill. Grinding the crown flush is the standard correction; the underlying fusion is rarely affected by the crown height alone.

Underfill and concavity

Underfill on a groove weld — where the weld face lies below the adjacent base metal plane — is not permitted under AWS D1.1 for full-penetration welds. The weld must be flush or have positive reinforcement within the limits above.

Concavity is most common on:

The root pass of a single-sided joint without backing, when burn-through is partial
Flush or flush-plus cover passes on CJP welds where the welder deliberately tried to hold a flat profile but undershot

For partial joint penetration (PJP) groove welds and fillet welds, concavity in the weld face (a slightly hollowed cross-section) is permitted within limits — typically the concavity cannot reduce the effective throat below the required minimum. PJP welds that rely on the theoretical throat dimension are most vulnerable; a concave face on a PJP groove weld directly reduces effective throat below the nominal value.

For related guidance on throat calculations, see PJP groove weld effective throat under AWS D1.1.

Fillet weld concavity (underfill at the toe)

Concavity at the toe of a fillet weld — where the weld face dips below the theoretical plane connecting the weld toes — is a separate condition from face convexity. AWS D1.1 permits concave fillet weld faces provided the required effective throat is maintained. However, if the concavity reduces the measured throat below the required value, the weld fails on throat, not profile.

The rule for CWIs: measure the throat first. If it meets the requirement, a concave face on a fillet weld passes profile. If the throat is short, additional weld metal must be deposited to restore the throat — not simply to fill the face profile.

Concave fillet welds tend to occur with:

High travel speed in the flat or horizontal position
GMAW spray transfer in short, fast passes
Voltage too high relative to amperage, flattening and spreading the bead

Undercut at the weld toe

Undercut — a groove melted into the base metal along the toe that is not filled by weld metal — is a profile defect closely related to convexity. High convexity with undercut is a common paired failure mode in GMAW and FCAW welds run at excessive voltage or travel speed.

AWS D1.1:2025 limits undercut to:

1/32 in (1 mm) for welds on cyclically loaded structures (demand critical, fatigue-sensitive)
1/16 in (2 mm) for statically loaded structures, in most cases, not to exceed 1/5 the base metal thickness

Undercut must be measured in depth perpendicular to the weld axis, not along the weld face surface.

For visual acceptance criteria beyond profile, including porosity, cracks, and incomplete fusion, see visual acceptance criteria under AWS D1.1.

Profile inspection on production welds: field practice

Good profile acceptance inspection requires:

Calibrated gauges. A Cambridge or Hi-Lo gauge and a dedicated fillet weld gauge set. Convexity scales are only on specialized gauges — not all fillet sets include them. Verify your gauge set covers convexity before using it for acceptance.

Consistent reference plane. For groove welds, the measurement datum is the base metal surface on both sides, not the weld itself. For fillet welds, the reference is the theoretical plane connecting the two toes. Poorly positioned gauges give false readings.

Both weld surfaces when accessible. On CJP joints welded from both sides (back-gouged and back-welded), both the face and root sides are subject to reinforcement and profile limits.

Documentation. When a profile defect is found, record the weld joint ID, the measured deviation, the required limit, and the corrective action taken. For weld repair documentation requirements, see weld repair documentation and corrective action under AWS D1.1.

Profile on the WPS

The WPS does not set profile limits — those come from the code. But the WPS controls the process parameters (current, voltage, travel speed, technique) that determine what profile the welder produces. A WPS that has been qualified within a narrow parameter range is more likely to produce consistent profiles than one with broad ranges.

When production welds consistently exhibit out-of-tolerance profiles, the first investigation should be WPS compliance: are the welders holding the specified travel speed? Is the voltage within the qualified range? A systematic profile failure on a joint type usually means the WPS parameters need refinement — not just that individual welds need repair.

If you need to track WPS qualification status and parameter ranges across your shop's procedure library, see how a digital WPS platform handles procedure compliance.

Rule library based on AWS D1.1:2025; verify against your governing edition. The authority having jurisdiction (AHJ) or contract may specify AWS D1.1:2020 or an earlier edition, which may have different table numbers or limit values.