AWS D1.3 · Structural Code · Sheet Steel

AWS D1.3 — Structural Welding Code for Sheet Steel

AWS D1.3 is the structural welding code for sheet steel and cold-formed members 3/16 inch (5 mm) or less. It covers five arc processes — GMAW, FCAW, SMAW, GTAW, and SAW — for thin gauge connections in light-gauge metal building systems and cold-formed steel framing.

Short-circuit transfer permitted: D1.3 explicitly allows GMAW short-circuit transfer for all sheet steel applications. This is the most significant process difference from D1.1, which excludes GMAW-S from prequalified WPSs.

What Is AWS D1.3?

AWS D1.3 governs structural welding of sheet steel under 3/16 inch (5 mm) thick. It addresses the unique challenges of thin material: burn-through prevention, distortion control, and sheet-to-structural connections. D1.3 explicitly permits GMAW short-circuit transfer (GMAW-S), which D1.1 does not prequalify.

AWS D1.3/D1.3M — Structural Welding Code — Sheet Steel — covers the arc welding requirements for structural sheet steel and cold-formed members where the thinnest connected part is 3/16 inch (5 mm) or less. The code applies to sheet steel with a minimum specified yield point up to 80 ksi (550 MPa), including both bare and galvanized steel. D1.3 also covers hollow structural sections (HSS) with wall thickness less than 1/8 inch (3 mm). It applies to sheet steel used in light-gauge metal building systems, cold-formed steel framing, metal deck attachments, curtain wall supports, and similar structural applications where thin materials govern the joint design.

The code addresses the unique challenges of welding thin sheet steel. Unlike structural plate covered by D1.1, sheet steel is susceptible to burn-through from excessive heat input, severe distortion from welding-induced residual stresses, and sheet-edge melting that reduces effective throat thickness. The welding parameters, joint designs, and acceptance criteria in D1.3 are specifically calibrated for thin material behavior rather than simply scaling down D1.1 requirements.

D1.3 establishes the boundary between sheet steel and structural steel welding at 3/16 inch (5 mm), which corresponds to approximately 7 gauge. Materials thicker than this boundary fall under D1.1 for general structural applications or D1.8 (which supplements D1.1) for seismic applications. When a sheet steel member is welded to a structural member exceeding 3/16 inch, the normative Annex A provides a clause-by-clause cross-reference governing which code applies to each aspect of the joint.

Welding Processes Under D1.3

D1.3 covers five arc processes: GMAW (including short-circuit transfer), FCAW, SMAW, GTAW, and SAW. GMAW short-circuit transfer is the primary production process for sheet steel because it provides precise heat input control at low amperages, reducing burn-through risk on thin material.

D1.3 permits five arc welding processes. The scope is explicitly limited to arc welding — all five processes use an electric arc between electrode and workpiece to create the weld.

GMAW (Gas Metal Arc Welding): The primary process for production sheet steel welding. D1.3 explicitly permits all GMAW transfer modes including short-circuit transfer (GMAW-S), which is the most common mode for sheet steel because it provides the lowest heat input, minimizing burn-through risk. This is a critical distinction from D1.1, which does not prequalify GMAW-S procedures. Spray transfer is generally too hot for material under 16 gauge. Pulsed spray can be used on heavier gauge material (10–7 gauge) for higher deposition rates with controlled heat input. GMAW, FCAW-G, and GTAW are restricted when wind exceeds 5 mph (8 kph) without adequate protection.
FCAW (Flux-Cored Arc Welding): Used for sheet steel welding where higher deposition rates are needed or where wind conditions make gas-shielded GMAW impractical. Self-shielded FCAW (FCAW-S) eliminates the need for external shielding gas, making it suitable for field welding of metal building components and is not subject to the 5 mph wind restriction. Gas-shielded FCAW (FCAW-G) provides better mechanical properties but requires wind protection per the same limit as GMAW.
SMAW (Shielded Metal Arc Welding): Permitted for sheet steel welding but requires careful technique to avoid burn-through. Small-diameter electrodes (3/32 inch) with fast travel speeds are typical. SMAW is less common than GMAW for sheet steel but remains useful for field repair and small-volume work where setting up wire feed equipment is impractical.
GTAW (Gas Tungsten Arc Welding): Provides the most precise heat control of all arc processes and is used for critical thin-gauge joints where burn-through risk is highest. GTAW is slower than GMAW but offers superior control on material under 18 gauge. Autogenous welding (no filler) is sometimes used on the thinnest sheet materials. Subject to the 5 mph wind restriction.
SAW (Submerged Arc Welding): Permitted under D1.3 for sheet steel applications where the material thickness and joint configuration can support the higher heat input. SAW is less common than GMAW for sheet steel but is used in automated production lines for heavier gauge material approaching the 3/16 inch boundary. Procedures using SAW that fall outside prequalified joint configurations require qualification by testing under Clause 6.

Prequalified WPS and Procedure Qualification

D1.3 Clause 5 provides prequalified WPS options for common sheet steel joints. Prequalified joint details, filler metals, and welding parameters are specified for sheet-to-sheet and sheet-to-structural connections. WPSs that fall outside prequalified limits require qualification by testing.

D1.3 provides a prequalified WPS path under Clause 5, similar in concept to D1.1’s prequalified system. WPSs using SMAW, GMAW, FCAW, or GTAW with specific joint configurations listed in Table 5.1 are designated as prequalified and may be used without qualification testing. These prequalified joints include square-groove butt joints, fillet welds, flare-groove welds, and arc spot and arc seam weld configurations — the joint types most commonly used in sheet steel construction.

Procedures that fall outside the prequalified joint configurations, use parameters beyond the prequalified ranges, or use SAW require qualification by testing under Clause 6. The essential variables for procedure requalification are defined in Table 6.2 and cover changes to welding process, filler metal, base metal, position, and key welding parameters.

Environmental and Thermal Requirements

D1.3 generally does not require preheat for sheet steel thicknesses. The thin material heats and cools rapidly, and the primary concern is controlling heat input to prevent burn-through and distortion rather than preventing hydrogen cracking. Interpass temperature limits may apply when specified.

D1.3 does not include a dedicated preheat table for sheet-to-sheet connections because thin sheet steel has low carbon equivalent, rapid heat dissipation that prevents hydrogen accumulation, and minimal restraint compared to thick structural members. These characteristics make hydrogen-induced cracking extremely unlikely in sheet-to-sheet connections.

Welding is prohibited when ambient air temperature is below 0°F (−18°C), when base metal is exposed to moisture (rain, snow), or — for GMAW, FCAW-G, and GTAW — when wind exceeds 5 mph (8 kph) without adequate protection. Cold weather welding requires parameter adjustments per Clause 7.4 for arc spot, arc seam, and arc plug welds.

For mixed-thickness connections where sheet steel is welded to structural members thicker than 3/16 inch, the structural member side must receive the preheat specified by D1.1 based on its own material category, hydrogen level, and thickness. The 2025 edition (7th) added Clause 7.5 to formally codify these base metal preheat and interpass temperature requirements for welding sheet steel to structural steel, differentiating groove and fillet welds from spot, seam, and plug welds. Previously this was governed by the normative Annex A cross-reference matrix.

Sheet-to-Structural Connections

D1.3 Annex A (normative) covers welding sheet steel to structural members governed by D1.1. When sheet steel attaches to structural steel, both D1.3 and D1.1 requirements apply. The preheat requirement follows D1.1 Table 5.11 based on the structural member thickness, not the sheet steel thickness.

One of the most practically important aspects of D1.3 is its treatment of connections between sheet steel members and structural steel members. These mixed-thickness joints are common in metal building construction where light-gauge purlins, girts, or deck panels are attached to structural steel frames, columns, or beams.

Mixed connections are governed by the normative Annex A, which provides a clause-by-clause cross-reference table (Table A.1) specifying whether D1.3 or D1.1 requirements apply to each aspect of the joint. Prequalified WPS paths do not apply to mixed sheet-to-structural connections — both codes require Clause 6 qualification testing for these joints. The weld size on a sheet-to-structural connection is limited by the sheet steel thickness to prevent burn-through. For fillet welds, the maximum leg size is typically the thickness of the sheet steel member.

When the structural member requires preheat, welder qualification under D1.1, or specific filler metal compatibility, those requirements apply to the structural member side of the joint per Annex A.

How D1.3 Compares to Other AWS Structural Codes

D1.3 governs sheet steel under 3/16 inch; D1.1 governs structural steel 1/8 inch and above. D1.3 permits GMAW short-circuit transfer as a prequalified process; D1.1 requires Clause 6 qualification for GMAW-S. D1.3 generally requires no preheat; D1.1 requires Table 5.11 lookup. Both share the same D1.x framework.

D1.3 vs D1.1 (Structural Steel)

D1.1 covers structural steel thicker than 3/16 inch, while D1.3 covers sheet steel at or below that threshold. D1.1 focuses on preventing hydrogen-induced cracking through preheat requirements (Table 5.11), controlling residual stress in thick sections, and ensuring adequate notch toughness. D1.3 focuses on preventing burn-through, controlling distortion, and qualifying arc spot and arc seam weld configurations that D1.1 does not cover. Both codes provide prequalified WPS options under their respective Clause 5 sections. D1.3 explicitly permits GMAW short-circuit transfer, which D1.1 excludes from prequalified WPSs — this is the most operationally significant process difference for fabricators working across both thickness ranges.

D1.3 vs D1.8 (Seismic Supplement)

D1.8 supplements D1.1 for seismic applications and does not directly address sheet steel. However, cold-formed steel framing in seismic regions may involve both D1.3 (for the sheet steel connections) and D1.8 (for the structural steel frame). The engineer of record must specify which code governs each connection in the seismic force-resisting system. D1.8 demand-critical weld requirements do not apply to sheet steel connections unless specifically invoked by the engineer.

D1.3 vs D1.4 (Reinforcing Steel)

D1.4 covers welding of reinforcing steel (rebar) to structural steel. When rebar is connected to sheet steel components (rare but possible in composite deck construction), D1.3 governs the sheet steel side and D1.4 governs the rebar side.

Aspect	D1.3 (Sheet Steel)	D1.1 (Structural)
Thickness range	Under 3/16 in (5 mm)	1/8 in (3 mm) and above
GMAW short-circuit	Permitted (primary mode)	Requires Clause 6 qualification
Preheat	Generally not required	Table 5.11 lookup
Primary concern	Burn-through, distortion	Hydrogen cracking
Prequalified WPS?	Yes (Clause 5)	Yes (Clause 5)
Sheet-to-structural	Normative Annex A	Not covered

Inspection and Acceptance Criteria

D1.3 inspection requirements account for thin material characteristics. Visual acceptance criteria address sheet steel-specific discontinuities including burn-through, edge melt-through, and underfill. Radiographic and ultrasonic testing are less common for sheet steel applications due to the thin gauge.

D1.3 acceptance criteria are tailored to the visual inspection challenges of thin material welds. Sheet steel welds are difficult to inspect visually because the heat-affected zone is narrow, weld profiles are small, and burn-through can be concealed by the joint configuration. The standard defines acceptance criteria for fillet weld size, undercut depth, porosity, incomplete fusion, and weld profile that are specific to thin material behavior.

Arc spot welds and arc seam welds have their own acceptance criteria based on visual appearance and, for qualification, peel testing and shear testing of sample coupons. Production quality for these configurations is verified through visual inspection and destructive testing at specified frequencies.

D1.1 Preheat Calculator →

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Frequently Asked Questions

What thickness range does AWS D1.3 cover?

AWS D1.3 covers structural welding of sheet steel and cold-formed members with a thickness of 3/16 inch (5 mm) or less. This corresponds to approximately 7-gauge steel and thinner. D1.3 also covers hollow structural sections (HSS) with wall thickness less than 1/8 inch (3 mm). Materials with a minimum specified yield point up to 80 ksi (550 MPa) are within scope. Materials thicker than 3/16 inch fall under AWS D1.1 for structural steel or D1.8 for seismic applications.

What welding processes are permitted under AWS D1.3?

AWS D1.3 permits five arc welding processes: SMAW (shielded metal arc welding), GMAW (gas metal arc welding), FCAW (flux-cored arc welding), GTAW (gas tungsten arc welding), and SAW (submerged arc welding). GMAW with short-circuit transfer is the most common process for sheet steel because it provides the low heat input needed to avoid burn-through on thin materials. D1.3 explicitly permits GMAW short-circuit transfer, which D1.1 excludes from prequalified WPSs.

Does AWS D1.3 require preheat?

D1.3 does not include a dedicated preheat table for sheet-to-sheet connections because thin sheet steel dissipates heat rapidly and is typically low-carbon, making hydrogen cracking unlikely. Welding is prohibited below 0 degrees Fahrenheit (-18 degrees Celsius) or when base metal is exposed to moisture. For mixed-thickness connections where sheet steel is welded to structural members thicker than 3/16 inch, Clause 7.5 (added in the 2025 edition) codifies the base metal preheat and interpass temperature requirements, requiring the structural member side to receive the preheat specified by D1.1.

What is the difference between AWS D1.3 and AWS D1.1?

AWS D1.1 covers structural steel thicker than 3/16 inch while D1.3 covers sheet steel 3/16 inch and thinner. D1.1 addresses hydrogen cracking through preheat tables (Table 5.11), while D1.3 focuses on burn-through prevention and distortion control. Both codes provide prequalified WPS options under their respective Clause 5 sections. D1.3 explicitly permits GMAW short-circuit transfer, which D1.1 excludes from prequalified WPSs. D1.3 also covers arc spot and arc seam weld configurations not addressed in D1.1.

How does D1.3 handle sheet-to-structural steel connections?

Mixed connections between sheet steel and structural steel are governed by the normative Annex A of D1.3, which provides a clause-by-clause cross-reference matrix specifying whether D1.3 or D1.1 requirements apply to each aspect of the joint. D1.3 governs the sheet steel side while D1.1 applies to the structural member side. Prequalified WPS paths do not apply to mixed sheet-to-structural connections — both codes require Clause 6 qualification testing for these joints.