AWS D1.1 vs D1.6: When Your Welder Needs Both Code Qualifications

Quick Answer: AWS D1.1 (Structural Welding Code: Steel, 2025 edition) governs carbon-steel structural welding. AWS D1.6 (Structural Welding Code: Stainless Steel) governs stainless work. A welder qualified to D1.1 is not automatically qualified to D1.6. Each code requires its own Welder Performance Qualification Record (WPQR), even if the welder uses the same process and position.

Defense and transportation weldments routinely combine carbon steel structure with stainless fluid-handling components, so any fabricator running multi-material defense work needs welders dual-qualified under both codes. Sourcing welders to only one code disqualifies the supplier on mixed-material RFQs.

A welder qualified to AWS D1.1 in the 6G position can run vertical, overhead, and horizontal welds on carbon steel pipe and plate all day. That same welder cannot legally lay a single bead on a 304L stainless steel bracket on a defense weldment, at least not under a code-compliant Welding Procedure Specification. The reason is AWS D1.6, the Structural Welding Code for Stainless Steel, which governs stainless work and requires its own separate Welder Performance Qualification Record.

For Prime contractors and OEMs sourcing multi-material weldments, this distinction is the difference between a quote that's bid-responsive and one that gets disqualified during supplier review.

What changed in AWS D1.1 in April 2025

The most recent revision to AWS D1.1 is D1.1/D1.1M:2025, released April 17, 2025. It is the 25th edition of the code and is currently the operative version for new welding procedure specifications and welder qualifications written after the release date. AWS publishes change-marked text (additions are underlined) making the delta from D1.1/D1.1M:2020 traceable for quality engineers updating WPS libraries.

The 2025 edition added a new high-strength structural steel grade to the prequalified base metal list, refined inspection guidelines, and clarified portions of the welder qualification section. Most fabricators upgrading from the 2020 version need to re-review their prequalified WPSs against the new flagged text rather than rewrite them from scratch.

The companion stainless code, AWS D1.6/D1.6M:2017 with Amendment 1, was not refreshed in parallel. It remains the operative stainless steel structural welding code as of 2026.

Where D1.1 ends and D1.6 begins

D1.1 governs structural welding of carbon and low-alloy structural steels, with the base metals listed in Annex M of the code. D1.6 governs structural welding of stainless steels: austenitic, ferritic, martensitic, duplex, and precipitation-hardening grades. The codes share architecture (a base metal list, a process list, a qualification system, an inspection chapter), but the rules diverge sharply on three points:

Filler metal classification. D1.1 specifies fillers per AWS A5.1 / A5.5 / A5.18 / A5.20 / A5.28 (carbon and low-alloy steel electrode classifications). D1.6 specifies fillers per AWS A5.4 / A5.9 / A5.22 (stainless steel and duplex stainless classifications). A welder running D1.6 work uses entirely different consumables (ER308L for austenitic stainless versus ER70S-6 for mild steel) and qualification is filler-specific.

Heat input and interpass temperature controls. D1.1 generally allows broad interpass temperature ranges for carbon steel. D1.6 caps interpass temperature aggressively to prevent chrome carbide precipitation in austenitic stainless (a 700°F-1500°F sensitization range) and intergranular corrosion. A welder running D1.6 work needs to manage the work envelope differently: preheat is rare on austenitic, interpass is restrictive.

Base metal thickness floor. D1.6 applies to stainless base metals 1/16 inch (1.5 mm) or thicker, typically 16 gauge and heavier. Thinner stainless gauges fall under AWS B2.1, the procedure and performance qualification standard for general sheet-metal-thickness welding. A fabricator working with both 12-gauge stainless body skins and 1/4-inch stainless brackets on the same weldment needs welders qualified under both D1.6 (for the brackets) and B2.1 (for the body).

When a welder needs both qualifications

Defense fabrication routinely produces parts where carbon steel and stainless steel are welded as a single assembly. Examples that appear regularly on Tier-2 defense purchase orders:

• Armored vehicle exhaust shrouds: stainless skin welded to a carbon steel support frame.
• Naval HVAC penetrations: stainless bulkhead inserts welded to carbon steel ship structure.
• Missile launcher rails: corrosion-resistant stainless insert plates joined to a low-alloy structural rail.
• Fire apparatus tank brackets: 304L stainless mounting plates welded to carbon steel subframe components.

A weldment like this requires two separate WPS documents (one for the carbon-steel side, one for the stainless side) and a welder who is qualified to both codes. A D1.1 6G qualification, the broadest plate-and-pipe qualification under the steel code, does not transfer to D1.6 work. The welder must execute a separate qualification test plate under D1.6 Section 4, with stainless filler, to be code-compliant on the stainless joints.

This is the most common procurement-side gap on defense supplier audits. A fabricator can have ten AWS-certified D1.1 welders on staff and still be unable to legally run a stainless-to-carbon weldment if none of them have completed D1.6 qualification.

Position qualification rules procurement engineers should understand

A welder qualification test plate is welded in a specific position (flat (1G), horizontal (2G), vertical (3G), or overhead (4G) on plate, or 5G/6G on pipe) and the position determines which production welds the welder may run. The rules carry over between D1.1 and D1.6, but the qualifying test itself does not.

| Test plate position | Production welds qualified | |---|---| | 1G plate (flat groove) | 1G groove only; 1F and 2F fillet | | 2G plate (horizontal groove) | 1G + 2G groove; 1F and 2F fillet; NOT vertical, NOT overhead | | 3G plate (vertical groove) | 1G, 2G, 3G groove; 1F, 2F, 3F fillet | | 4G plate (overhead groove) | 1G + 4G groove; 1F, 2F, 4F fillet | | 3G + 4G combined | All-position groove and fillet on plate | | 6G pipe (45° inclined) | All-position groove on plate and pipe; universal |

Procurement officers sometimes assume 2G qualifies a welder for "vertical position." It does not. A 2G test plate is welded horizontally; the welder is qualified to weld horizontally and flat only.

How New Tech Metals handles multi-code weldments

New Tech Metals maintains AWS Certified Welders qualified across the full D1-series codes referenced on defense weldments: D1.1 (steel), D1.2 (aluminum), D1.3 (sheet steel), D1.6 (stainless), and D9.1 (non-structural sheet metal). The qualification matrix is maintained per welder per code, with WPQR records retained per the code's continuity-of-qualification requirements.

For a multi-material weldment, the quoting process matches each weld symbol on the engineering drawing to the appropriate code and qualified welder before the part is scheduled to the floor, not after.

Action

If you are releasing a multi-material weldment drawing, ask your fabricator two questions before placing the PO: which AWS code each weld is qualified under, and whether the assigned welders hold current qualification records under each code on the drawing. A fabricator that answers both without referring back to a supplier is materially less risky on first-article delivery.

For multi-code weldment quotes, request a quote from New Tech Metals.