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What Clause 7.13 Requires

Clause 7.13 of D1.1:2025 states that the minimum fillet weld size, except for fillet welds used to reinforce groove welds, shall be as shown in Table 7.7. The minimum fillet weld size shall apply in all cases, unless the design drawings specify welds of a larger size.

This is a fabrication requirement, not a design requirement. The Engineer sizes the weld based on load. Table 7.7 establishes a floor — the weld can never be smaller than the table value for a given base metal thickness, regardless of what the calculated load would allow.

Table 7.7: Minimum Fillet Weld Sizes

Three footnotes modify how you read this table. Each one addresses a situation that changes the effective requirement. Most online references reproduce the four rows above and stop there. The footnotes are where the real code knowledge lives.

Footnote a: Which Thickness Is T?

Footnote a is the most consequential note in Table 7.7. It defines what T means, and the answer depends on your welding process:

Non-low-hydrogen processes without preheat calculated per Clause 6.8.4: T equals the thickness of the thicker part joined. Single-pass welds shall be used. This means your minimum weld size is driven by the heavier member, and you must deposit the full size in one pass.

Low-hydrogen processes (and non-low-hydrogen with preheat calculated per Clause 6.8.4): T equals the thickness of the thinner part joined. The single-pass requirement does not apply. This means your minimum weld size is driven by the lighter member, and you can build up the size in multiple passes.

Consider a joint between a 1 in column flange and a 3/8 in connection plate. With E7018 (low-hydrogen), T = 3/8 in (thinner part), so the minimum fillet weld is 3/16 in. With E6013 (non-low-hydrogen, no preheat calculated per 6.8.4), T = 1 in (thicker part), so the minimum jumps to 5/16 in — and it must be deposited in a single pass.

If you need to determine whether your process qualifies as low-hydrogen for Table 7.7 purposes, start with your preheat requirements — the electrode classification drives both the preheat category and the footnote a interpretation.

The reason for this distinction is metallurgical. Non-low-hydrogen electrodes produce higher diffusible hydrogen in the weld deposit. A thicker base metal acts as a larger heat sink, cooling the weld faster and increasing the risk of hydrogen-induced cracking. Requiring the minimum size to be based on the thicker member ensures adequate heat input into the joint. The single-pass restriction prevents the welder from depositing a thin first pass that cools too rapidly against the heavy member.

Footnote b: The Thin-Member Escape Clause

Footnote b states that the weld size need not exceed the thickness of the thinner part joined. This prevents an absurd result when a very thin member is attached to a very thick one.

If you weld a 3/16 in gusset to a 1-1/2 in thick base plate using E7018, Table 7.7 would require a 3/16 in minimum fillet (T = 3/16 in, thinner part). That happens to equal the gusset thickness, which is fine. But if someone welded the same gusset with a non-low-hydrogen process (T = 1-1/2 in, thicker part), the table would call for 5/16 in — larger than the gusset itself. Footnote b caps the requirement at 3/16 in, the gusset thickness.

In practice, footnote b most often applies when thin plates, angles, or channels are connected to heavy wide-flange sections. The Engineer will typically specify a weld size based on load, and that calculated size will usually govern over the Table 7.7 minimum for thin-to-thick joints.

Footnote c: Cyclic Loading Override

Footnote c states that the minimum size for cyclically loaded structures shall be 3/16 in [5 mm]. This overrides the 1/8 in [3 mm] value in the first row of the table.

For base metal 1/4 in and under in a statically loaded structure, the minimum fillet weld is 1/8 in. For the same thickness in a cyclically loaded structure — a bridge, a crane runway girder, or any connection subject to fatigue — the minimum increases to 3/16 in. The second through fourth rows already require 3/16 in or more, so footnote c only changes the outcome for the thinnest material.

The rationale is fatigue performance. A 1/8 in fillet weld on a cyclically loaded joint has minimal throat area to resist repeated stress reversals. The 3/16 in floor provides a larger effective throat and a less severe stress concentration at the weld toe.

How Table 7.7 Interacts with Design Requirements

Table 7.7 is a minimum, not a design tool. The Engineer calculates the required weld size per Clause 4 based on applied loads. If the calculated size exceeds the Table 7.7 minimum, the calculated size governs. If the calculated size is less than the Table 7.7 minimum, the table value governs.

There is also an upper limit. Clause 4.5.2.9 limits the maximum fillet weld size on the edge of material less than 1/4 in thick to the material thickness. For material 1/4 in or greater, the maximum size along edges shall be 1/16 in less than the material thickness, unless the weld is specifically designated on the drawings to be built out to obtain full throat thickness.

These constraints create a window: your fillet weld must be at least the Table 7.7 minimum and no more than the Clause 4.5.2.9 maximum (when welding along an edge), with the Engineer’s calculated size falling somewhere in between.

D1.1 Table 7.7 vs AISC Table J2.4

AISC 360 Table J2.4 also specifies minimum fillet weld sizes, but it always uses the thickness of the thicker part joined — with no process distinction. D1.1 Table 7.7 footnote a makes the controlling thickness depend on whether you use a low-hydrogen process. When D1.1 is the contract document, Table 7.7 governs. In practice, AISC Table J2.4 is more conservative for low-hydrogen processes because it does not allow you to use the thinner part. If your project references both AISC 360 and D1.1, the more restrictive requirement applies unless the Engineer specifies otherwise.

Common Mistakes

Ignoring footnote a entirely. Many fabricators and even some inspectors read only the four rows and always use the thicker member. With low-hydrogen processes, this overestimates the requirement and wastes filler metal and time.

Using multi-pass with non-low-hydrogen electrodes. When footnote a requires single-pass welds, a two-pass fillet deposited with E6013 does not comply, even if the final size meets the table. The inspector can reject the weld on procedure alone.

Forgetting footnote c on cyclic structures. A 1/8 in fillet weld on a bridge connection fails the minimum regardless of load calculation. The 3/16 in cyclic floor applies.

Confusing minimum size with design size. Table 7.7 does not replace the Engineer’s weld size calculation. A WPS that calls out 3/16 in because the table minimum is 3/16 in, when the connection actually requires 5/16 in per the design drawings, is undersized.

Once the weld is deposited, the inspector evaluates it against Table 8.1 acceptance criteria. An undersized fillet weld is one of the discontinuities addressed there. For the full list of visual inspection criteria, see the weld defects overview.