Is there a maximum fillet weld size that can be made in a single pass under AWS D1.1?

AWS D1.1:2025 prequalified WPS provisions limit single-pass fillet weld sizes based on welding process and position. Prequalified maximum single-pass sizes for SMAW are 5/16 in (8 mm) flat and horizontal, and 1/4 in (6 mm) vertical and overhead. FCAW-G and SAW can qualify larger single-pass deposits, but only through tested WPS qualification.

Does making a fillet weld in one pass vs. multiple passes change the WPS essential variables?

The number of passes is not itself a D1.1 essential variable, but single-pass vs. multi-pass often changes heat input, interpass temperature, and deposition sequence — all of which must be within the documented WPS range. Exceeding heat input or departing from the qualified pass count without a supporting PQR is a WPS deviation.

Can I run a larger single-pass fillet weld on a PQR-qualified WPS than I could on a prequalified WPS?

Yes. A tested WPS supported by a PQR can qualify single-pass fillet weld sizes beyond the prequalified limits, provided the PQR test weld was deposited in a single pass and the mechanical tests demonstrate acceptance. The qualification range is based on what was actually tested.

What mechanical property differences exist between single-pass and multi-pass fillet welds?

Multi-pass welds benefit from the thermal cycle of subsequent passes annealing the previous deposit, which can improve HAZ toughness and reduce residual stress. Single-pass welds retain higher heat input effects in the HAZ and weld metal, which can affect notch toughness in toughness-critical applications. This is one reason CVN-qualified WPSs typically specify multi-pass deposition for structural applications.

Single-Pass vs. Multi-Pass Fillet Welds Under AWS D1.1

When can a fillet weld be deposited in a single pass? AWS D1.1 prequalified limits, heat input implications, and WPS documentation requirements explained for CWIs and fab shop QC managers.

Not every fillet weld requires multiple passes, and the choice between single-pass and multi-pass deposition affects more than just productivity. It affects heat input, HAZ properties, interpass temperature tracking requirements, and in some cases the mechanical qualification basis for the weld. A WPS that is silent on the number of passes — or that states "as required" without a documented range — is a WPS that will generate questions during a CWI review.

This article explains when AWS D1.1 permits single-pass fillet welds, what limits apply, and how to correctly document pass requirements on the WPS.

What the Prequalified WPS Provisions Allow

AWS D1.1:2025 Clause 5 defines the prequalified WPS requirements — the conditions under which a WPS may be used without supporting PQR test results. For fillet welds made on prequalified joints with prequalified processes and base metals, the code sets maximum single-pass fillet weld sizes by process and position.

For SMAW prequalified WPS:

Flat (1F) and horizontal (2F) positions: maximum single-pass fillet weld size is 5/16 in (8 mm)
Vertical (3F) and overhead (4F) positions: maximum single-pass fillet weld size is 1/4 in (6 mm)

For FCAW-G and GMAW prequalified WPS: prequalified single-pass limits are more permissive than SMAW because of higher deposition efficiency, but the applicable maximums depend on wire diameter and position. For production fillet welds larger than these limits, the prequalified WPS requires multi-pass deposition.

For SAW: submerged arc can produce significantly larger single-pass deposits in flat and horizontal positions. Single-pass SAW fillet welds up to 5/8 in (16 mm) or larger can be qualified through testing. Because of the high heat input associated with large single-pass SAW welds, most WPSs for structural work specify multi-pass above the prequalified limits.

Rule library based on AWS D1.1:2025; verify against your governing edition.

Why Single-Pass Limits Exist

The limits exist primarily to control heat input and the resulting metallurgical effects on the base metal and weld deposit.

A large single-pass fillet weld concentrates more heat into the base metal than a multi-pass sequence with the same total deposit. Higher heat input produces a wider, softer heat-affected zone (HAZ), slower cooling rates, and in some steels, grain coarsening that reduces toughness. In thin base metal, a single large pass can distort the joint or melt through. In thick base metal, the rapid cooling of a very large single-pass deposit can cause hydrogen-assisted cracking if preheat is marginal.

Multi-pass deposition allows each pass to be within the heat input range supported by the PQR, distributes the thermal cycle across the joint cross-section, and allows subsequent passes to partly anneal the previous deposit — improving HAZ toughness and reducing peak residual stress. This is why CVN-toughness-critical joints almost always specify multi-pass deposition.

Heat Input Documentation on the WPS

Whether a fillet weld is single-pass or multi-pass, the WPS must state the applicable heat input range. AWS D1.1:2025 requires WPS documentation of amperage, voltage, and travel speed — from which heat input is calculated:

HI (kJ/in) = (Amperage × Voltage × 60) ÷ (Travel Speed in in/min × 1000)

For a prequalified WPS, the heat input for the largest single-pass fillet must still fall within the qualified range implied by the base metal, process, and preheat combination. For a tested WPS, the heat input used during PQR testing defines the upper limit for production use, and no pass — whether in a single-pass or multi-pass sequence — may exceed the maximum heat input on the WPS.

For a deeper look at how heat input is calculated and what changes it, see arc energy and heat input calculation under AWS D1.1.

Interpass Temperature in Multi-Pass Sequences

When multiple passes are required, interpass temperature becomes an active inspection parameter. AWS D1.1 sets a maximum interpass temperature on the WPS — the maximum temperature the previously deposited pass may reach before the next pass is started. Exceeding maximum interpass temperature is an essential variable violation.

The CWI must verify interpass temperature at the start of each pass in a multi-pass sequence, not just before the root pass. Contact pyrometers, temperature-indicating crayons (Tempilstiks), or infrared thermometers are acceptable measurement methods, but the method used must be consistent with the WPS.

If a production fillet weld cools below the minimum preheat between passes, the sequence must stop until preheat is restored — and that restoration must be documented. See interpass temperature control for structural welding for the full inspection protocol.

WPS Documentation: What Must Be Stated

A WPS covering fillet welds — whether single-pass or multi-pass — must document:

Number of passes: for multi-pass welds, the minimum and maximum number of passes (or a pass range) should be stated. "As required" is not adequate documentation.
Pass sequence: for complex joints with multiple fillet welds on the same connection, the deposition sequence should be specified to manage distortion and residual stress.
Heat input range per pass: amperage, voltage, and travel speed ranges that define the permissible production window.
Maximum single-pass deposit size: if the WPS allows single-pass production, the maximum fillet size must be stated and must not exceed the prequalified limit (or the tested limit from the PQR).
Bead type: stringer beads vs. weave beads have different heat input implications. AWS D1.1 typically restricts weave width — see stringer vs. weave bead WPS requirements for specifics.

For multi-pass welds, also document interpass temperature limits (both minimum preheat maintenance and maximum interpass temperature) and any required interpass cleaning between passes.

Practical Decision-Making for CWIs and QC Managers

On the shop floor, the decision to make a fillet weld in one pass or multiple passes usually comes from the WPS — if it is written correctly. Problems arise when:

The WPS allows a single-pass fillet weld size that the welder cannot deposit within the qualified heat input range. A large single-pass fillet at slow travel speed can easily exceed the maximum heat input on the WPS, invalidating the procedure.
The welder makes a multi-pass fillet where the WPS specifies single-pass (or vice versa) because the WPS is ambiguous. Unclear WPS language is a quality system failure, not just a welder failure.
The production fillet weld size differs from the WPS. If a 1/4-in fillet is specified on the drawing but the welder deposits a 3/8-in fillet in one pass, that may exceed the qualified single-pass limit and introduce heat input outside the tested range.
Toughness-critical applications allow single-pass where they should not. On connections requiring CVN toughness, the WPS should be reviewed to confirm that multi-pass deposition is required.

The CWI reviewing in-process work should verify that the observed number of passes matches the WPS, that bead size is consistent with the stated range, and that travel speed and amperage are within the documented limits. If you need to manage multiple WPSs across projects with different fillet weld size and pass requirements, see fillet weld size and WPS requirements and consider how a structured WPS library keeps these variables tracked per job. A purpose-built WPS platform like this one lets QC managers assign specific WPS revisions to specific connections, reducing the ambiguity that leads to single-pass violations.