When does AWS D1.3 apply instead of AWS D1.1?

AWS D1.3, Structural Welding Code — Sheet Steel, applies to arc welding of cold-formed steel members and connections where base metal thickness is 0.18 inches (4.6 mm) or less (or in some situations up to 0.25 inches). AWS D1.1 applies to structural steel plate and shapes typically 1/8 inch thick and above. When both thin sheet and heavier sections are present, D1.3 governs the sheet portions and D1.1 governs the heavier sections.

Does AWS D1.3 permit prequalified WPS procedures?

Yes. AWS D1.3 includes prequalified joint details and welding conditions similar to D1.1's prequalified status. However, the base metals, joint geometries, and process parameters permitted for prequalified status differ significantly from D1.1. The CWI must verify that the specific joint, base metal, and welding process all appear in the D1.3 prequalified provisions, not D1.1.

Can a welder qualified under AWS D1.1 weld sheet steel under D1.3?

Not automatically. AWS D1.3 has its own welder qualification tests. D1.1 qualification does not transfer to D1.3, and D1.3 qualification does not transfer to D1.1. A fabricator whose welders are qualified only to D1.1 must qualify them separately under D1.3 before welding sheet steel structural connections.

What are the most common WPS mistakes on light-gauge steel jobs?

Three are common: writing the WPS to D1.1 instead of D1.3 because the shop uses D1.1 for everything else; failing to list the sheet steel ASTM specification (ASTM A1003 is the general-purpose sheet steel spec for D1.3 prequalified work); and using SMAW electrodes sized for heavy plate without recognizing that burnthrough and distortion limits on light gauge require smaller electrodes and lower heat input.

WPS Requirements Under AWS D1.3 for Sheet Steel Welding

AWS D1.3 governs structural welding of sheet steel, not D1.1. Here's how WPS qualification differs, what prequalified joints exist, and where fab shops get it wrong.

Walk through most fab shops and you will find one WPS library for structural steel. Ask how the shop handles light-gauge sheet steel connections — collector plates, cold-formed purlin clips, deck-to-beam fillet welds, thin gussets — and the answer is often the same D1.1 procedures, stretched to cover material they were not qualified for.

AWS D1.3 is a separate code from AWS D1.1. It was written specifically because the challenges of welding thin sheet steel — burnthrough, distortion, incomplete fusion at the weld root, and heat-affected zone softening — are different enough from heavy structural welding that a single code could not address both properly. When the project specification calls out D1.3, or when the fabricated members are cold-formed sheet steel components, the WPS must be written and qualified to D1.3.

What D1.3 covers (and what it does not)

AWS D1.3 covers arc welding of cold-formed steel structural members and connections where the thinner of the base metals being joined is 0.18 inches (4.6 mm) or less. The code addresses SMAW, GMAW, FCAW, and GTAW processes on sheet steel — the same processes as D1.1, but with different parameter ranges reflecting the low heat input and shallow penetration requirements of light-gauge work.

D1.3 does not cover:

Material thicker than 0.18 in unless both pieces are under that threshold
Pressure vessels or pressure piping
Stud welding (governed by the stud welding provisions in D1.1 or the stud manufacturer's specification)
Resistance welding or spot welding

When a fabricated assembly includes both sheet steel members (governed by D1.3) and heavy structural members (governed by D1.1), each category of connection must use a WPS written to the applicable code. Combining both requirements in a single WPS is only acceptable when the WPS is explicitly qualified under both codes, which requires separate testing to both standards.

Prequalified provisions under D1.3

Like D1.1, AWS D1.3 offers prequalified welding conditions. Prequalified status means a WPS that conforms to all listed requirements does not require supporting PQR coupon testing to be used in production. The prequalified provisions in D1.3 include:

Base metals. ASTM A1003 (sheet steel for structural framing) is the primary prequalified base metal. ASTM A653 (galvanized/zinc-coated sheet), ASTM A792 (aluminum-zinc alloy-coated), and certain other ASTM sheet products appear in the D1.3 prequalified tables. Each specification must be verified in the applicable edition of the code — some editions have expanded or restricted the list.

Joint geometry. D1.3 prequalified joints include flare-bevel groove welds (the most common joint type for cold-formed sections), flare-V grooves, fillet welds, and lap welds. Joint dimensions — root opening, angle, and land — are specified for each type. The flare-bevel groove weld is particularly important because it appears in virtually every cold-formed steel connection: a round-cornered C-section or hat section meets a flat plate, and the flare of the rounded corner creates the natural groove geometry.

Effective throat and size limits. Because sheet steel thickness is the binding dimension, D1.3 specifies effective throat sizes as a function of base metal thickness — not absolute dimensions. A WPS written to D1.3 must reflect these thickness-based calculations, not the fixed weld size minimums from D1.1.

Writing the D1.3 WPS: what to include

A D1.3 WPS follows the same general format as a D1.1 WPS — process, base metal, filler metal, preheat, position, and joint geometry — but the D1.3-specific requirements differ in several areas.

Base metal specification. State the ASTM specification and coating condition. Galvanized (ASTM A653) and uncoated (ASTM A1003) are not interchangeable on the same WPS without explicit qualification that covers galvanized coatings. Galvanized sheet welds produce zinc fumes and affect fusion behavior.

Electrode diameter. Sheet steel welding demands smaller electrodes than heavy structural work. SMAW on 12-gauge sheet typically uses 3/32 in or 1/8 in E6011 or E6013 electrodes. Using a 5/32 in E7018 — standard for structural plate — on thin sheet will produce burnthrough, excessive spatter, and distortion. The WPS must specify electrode diameter, not just classification.

Travel speed range. Heat input on thin material is controlled by travel speed. Specifying a travel speed range — minimum and maximum — is more meaningful on a D1.3 WPS than on a heavy structural WPS because travel speed is the primary variable the welder uses to avoid burnthrough. Some D1.3 WPS documents express this as a maximum heat input per unit length.

Weld access and fitup. Cold-formed sections have manufacturing tolerances that are wider than cut structural shapes. Allowable root opening and fitup tolerances on D1.3 joints reflect this. The WPS and associated joint detail must state the acceptable fitup range, because a gap that would be acceptable for a plate groove weld is too wide for a thin sheet lap fillet.

Welder qualification under D1.3

AWS D1.3 requires welder qualification testing under the code's own provisions, not D1.1. A welder who has passed the D1.1 3G and 4G position tests is not automatically qualified to weld to D1.3. The qualification tests under D1.3 are designed for the specific challenges of sheet steel, including:

Macroetch examination of cross-sections showing full fusion into both members
Visual and dimensional acceptance criteria for throat size relative to material thickness
Ductility bend tests that differ from the heavy-plate guided bend tests under D1.1

Welder qualification records (WPQ) under D1.3 should identify the base metal thickness range qualified, the process and electrode, and the position tested. For a fab shop that maintains a combined welder qualification matrix for D1.1 work, D1.3 qualifications must be tracked separately. See welder performance qualification under AWS D1.1 for how WPQ records are structured — the same recordkeeping principles apply under D1.3.

Common mistakes when D1.3 applies

Writing the WPS to D1.1. This is the most frequent error. A shop that runs 95% D1.1 work defaults to D1.1 WPS procedures for everything. When the project specification explicitly calls out D1.3 for the light-gauge elements, using a D1.1 WPS is a nonconformance regardless of whether the weld quality appears acceptable visually.

Ignoring the coating. Galvanized sheet steel is everywhere in light commercial and metal building construction. The coating is not mentioned on many WPS documents. AWS D1.3 addresses zinc-coated materials specifically — including ventilation requirements for zinc fume, the need to remove or locally strip zinc at the weld area where required, and the effect of the coating on fusion and porosity. A WPS for galvanized sheet should identify the coating and reference the applicable provisions.

Using D1.1 visual acceptance criteria. D1.3 has its own visual inspection acceptance criteria that account for sheet steel dimensions. Applying D1.1 weld size minimums to thin sheet connections can lead to both false rejects (a fillet weld that meets D1.3 but is flagged as undersized by D1.1 limits) and false acceptance (a D1.3-deficient weld that appears to meet D1.1 criteria).

No WPS at the point of use. Cold-formed sheet steel connections are often treated as secondary work — clips, braces, framing angles, thin gussets. In some shops, these connections are welded without any WPS on the floor. Under D1.3, the WPS must be accessible at the point of welding just as it would be for any D1.1 joint.

Integrating D1.3 into an existing WPS library

For a shop that primarily does D1.1 structural work and occasionally takes on light-gauge projects, the D1.3 WPS library does not need to be large. A set of four or five prequalified WPS procedures — one per process (SMAW, GMAW) covering common joint types (flare-bevel, fillet, lap) and the base metals most common in the region's light commercial market — covers most situations.

The key is keeping D1.3 and D1.1 procedures clearly separated in the WPS numbering scheme. A notation like "D1.3-GMAW-01" rather than a number that could be confused with a D1.1 procedure eliminates the risk of pulling the wrong WPS on a mixed project. See WPS numbering scheme best practices for a systematic approach to keeping procedure libraries organized across multiple codes.

Where the project involves both light-gauge sheet steel and heavy structural members — a steel framing system with moment-frame columns and light-gauge purlin bracing, for example — document in the project quality plan which procedures govern which connections. The audit trail should be unambiguous.

Rule library based on AWS D1.1:2025; verify against your governing edition. AWS D1.3 references are to AWS D1.3/D1.3M:2018. Confirm the edition specified by your project's authority having jurisdiction.

If your shop is building out a WPS library that covers both D1.1 structural and D1.3 sheet steel work, WPS software that supports multiple code libraries keeps procedures separated, searchable, and linked to the right welder qualifications.