Intermittent Fillet Welds: AWS D1.1:2025 Length and Spacing Rules

Intermittent fillet welds appear everywhere in structural steel fabrication — on longitudinal seams of plate girders, on gusset-to-web connections, and on stiffener attachments where a continuous weld is not required by the structural engineer. When misapplied, they produce welds that are too short, spaced too far apart, or inconsistent in size. Each of those conditions is a code violation, and all of them show up on AISC audit and third-party CWI walk-downs.

Understanding the AWS D1.1:2025 rules for intermittent fillet welds — minimum length, spacing limits, weld symbol notation, and inspection approach — keeps a production run clean and defensible.

Rule library based on AWS D1.1:2025; verify against your governing edition (the AHJ or contract may specify 2020 or an earlier edition).

What Intermittent Fillet Welds Are and When They Are Used

An intermittent fillet weld is a series of short weld segments separated by unwelded gaps, as opposed to a continuous fillet running the full joint length. The weld symbol on the drawing uses a length-pitch notation: a callout like 3/16–2–6 means a 3/16 in. fillet weld, 2 in. long, at 6 in. center-to-center pitch.

Structural engineers specify intermittent fillets when the strength demand does not require a continuous weld, or when distortion control on thin plates makes a continuous weld counterproductive. Common locations:

• Longitudinal fillet welds attaching web plates to flanges in built-up girders (secondary attachment zones)
• Stiffener-to-web welds where the stiffener is non-load-bearing (bearing stiffeners typically require continuous or near-continuous welds)
• Base plate fillet welds on light column bases with low uplift demand
• Gusset plate edges where tearing is not the governing failure mode

The structural engineer's drawing dictates whether intermittent welds are permitted. A CWI's job is to verify that the welds actually placed match the symbol and comply with the code.

Minimum Effective Length: The 4× Rule

AWS D1.1:2025 limits the minimum effective length of a fillet weld to four times the nominal weld size. A weld shorter than that does not develop the full cross-section capacity assumed in design.

In practice:

If the available joint length cannot accommodate the minimum segment length at the specified pitch, the weld size must be increased or the design must change. A CWI measuring a short fillet segment should not accept it on the grounds that "there was not enough room" — that is a design coordination issue, not a field variance.

Note that effective length is measured along the axis of the weld, not the nominal callout. Start and stop craters do not count as effective length if they are significantly undersized. In practice, experienced CWIs discount the first and last 1/4 in. of a start-stop and expect the stated length to be met on the interior.

Maximum Spacing: The Rules That Vary by Application

Spacing limits for intermittent fillet welds depend on how the plates are loaded and which element they connect. AWS D1.1 establishes different maximums for compression members, tension members, and certain special cases. These are limits on center-to-center pitch (the full repeat distance, segment plus gap), not gap alone.

Compression element spacing: When intermittent fillets connect a plate in compression (for example, attaching a cover plate or flange element that is stressed in compression), the pitch must be small enough that the two connected elements act compositely. Exceeding the compression spacing limit can cause a thin plate to buckle in the gap.

Tension element spacing: The spacing limit for tension applications is less restrictive because there is no buckling concern. Plates in tension that are locally unsupported between weld segments can still develop the design force provided the welds carry their share.

Practical guidance for common cases: For non-structural stiffener attachments and secondary connections, the drawing typically specifies the pitch directly. Use that dimension and verify it on every assembly. Where the drawing says only "intermittent, 6 in. pitch" without more detail, confirm with the EOR or shop engineer that the spacing meets the applicable code limit for the loading condition.

Weld access and end returns: AWS D1.1 also addresses how intermittent fillet sequences terminate at plate edges. End returns and start/stop placements near free edges must be treated carefully to avoid unplanned cracks propagating from the weld toe. The code permits omitting end returns on intermittent welds where they are not required for strength, but your WPS and fabrication drawings should document the approach.

Chain vs. Staggered: Which Is Better?

Chain intermittent fillets are placed directly across from each other on opposite sides of a web, plate, or stem. Every weld segment on the left lines up with a corresponding segment on the right. This is the simpler layout and is easier for welders to pace.

Staggered intermittent fillets offset the segments so that the gap on one side falls opposite the weld on the other side. The weld symbol shows the segments placed on alternating sides of the reference line to indicate this pattern.

From a distortion and heat input standpoint, staggered fillets are preferred on thinner plates (roughly under 3/8 in.) because the thermal cycles from opposite sides do not overlap in the same transverse cross-section simultaneously. This reduces angular distortion on light members.

From an inspection standpoint, chain fillets are easier to measure. Both patterns must meet the same minimum length and pitch requirements. When the drawing specifies staggered but the shop ran chain, that is a nonconformance requiring disposition.

WPS Requirements for Intermittent Fillets

The WPS does not need to specify "intermittent" as a distinct parameter. The essential variables that trigger requalification under AWS D1.1:2025 Table 6.6 relate to process, base metal, filler metal, position, current type, and similar factors — not whether the weld is continuous or intermittent.

What the WPS must cover:

• Process and filler metal: The electrode classification, diameter, and applicable F-number must be within the WPS range.
• Weld size range: The WPS must cover the fillet size being deposited. A WPS qualified for 3/8 in. maximum fillet does not cover a 1/2 in. fillet, even in intermittent segments.
• Position: Intermittent fillets in the flat and horizontal positions are often straightforward, but overhead or vertical intermittent segments require a WPS qualified for that position.
• Base metal group: AWS D1.1:2025 Table 6.6 addresses base metal group changes. Confirm the steel grades for both pieces being joined.

The welder must hold a valid WPQ for the process and position. A welder whose qualification has been run in the flat position only is not qualified to place overhead intermittent fillets, regardless of how short the segments are.

For pricing and WPS management resources, see WPS Welding pricing plans — the platform tracks WPS coverage against your active material and position combinations.

How CWIs Inspect Intermittent Fillet Welds

Walk-down inspection of intermittent fillet welds covers these items:

1. Weld size. Use a fillet weld gauge — fixed-size bridge cams, adjustable gauges, or machined straight-edge gauges are all acceptable. Measure the minimum throat or the leg length, depending on the gauge type. Measure at least three points per segment: near each end and the middle. Record the minimum.

2. Segment length. Tape measure from start-of-weld to end-of-weld on each segment. Reject segments that do not meet the length callout within normal measurement tolerance (typically ±1/16 in. for short segments). Short segments from poor arc starts should be completed before the assembly moves.

3. Center-to-center pitch. Measure from the midpoint of one segment to the midpoint of the next. The pitch should match the drawing callout. Isolated long gaps (welder skipped a location) are nonconformances.

4. Visual quality. Check for undercut, overlap, and visible cracks at segment start-stops. Start-stop porosity is common on SMAW intermittent welds and should not exceed the limits in the applicable acceptance criteria table.

5. Coverage. Count the number of segments on each joint and compare to the drawing. Missing segments are common on complex gusset arrangements.

Document findings on the inspection record by piece mark and joint. Nonconformances should generate an NCR tied to the specific joint identifier.

Weld Symbol Reading for Intermittent Fillets

On structural drawings, the length-pitch notation appears directly on the weld symbol:

• Arrow-side intermittent: The notation is below the reference line: 3/16-2-6 means 3/16 in. fillet, 2 in. long, 6 in. pitch.
• Other-side intermittent: The notation is above the reference line.
• Both-side chain: Both sides carry the same notation. Segments are aligned.
• Both-side staggered: Both sides carry the notation, but the segments on one side are shown offset on the symbol. The tail or note may indicate stagger.

A CWI who cannot read the weld symbol correctly cannot inspect the weld correctly. When symbols are unclear or ambiguous, request clarification from the EOR before the welds are placed — not after.

Common Errors Found on AISC Audits

In AISC fabricator certification audits and third-party compliance reviews, the most common intermittent fillet weld violations are:

1. Segments shorter than the minimum length. Welders sometimes stop early at natural breaking points (plate edge, stiffener clip, penetration). Every segment must meet the minimum.

2. Inconsistent pitch. The first several segments are correctly spaced, then the spacing drifts as the welder moves down a long plate. At 10 feet, the pitch errors compound.

3. Wrong side placement. On staggered patterns, welders occasionally run both sides in alignment, producing chain fillets instead.

4. Undersized starts and stops. The first and last 1/4 in. of a SMAW or FCAW weld segment are often underfilled. On short segments (under 2 in.), this proportionally reduces effective length more than on long welds.

5. Chain instead of staggered when stagger is specified. This is a drawing deviation requiring documentation and, depending on the structural engineer's assessment, potential retrofit.

For an overview of the broader CWI review process for WPS compliance, see CWI WPS review checklist and Weld inspection hold points for CWIs.

Summary

Intermittent fillet welds are common, cost-effective, and frequently misapplied. The AWS D1.1:2025 rules are not complicated, but they do require consistent application: every segment must meet minimum length (4× the weld size), spacing must comply with the applicable limit for the loading condition, and both chain and staggered patterns must match the engineering drawing. CWI inspection covers size, length, pitch, visual quality, and count — not just a walk-by glance. Document findings by joint so that any nonconformance has a clear disposition trail before the assembly ships.