AWS D1.1 vs. D17.1: Which Welding Code Applies to Your Project?

AWS D1.1 and AWS D17.1 are both American Welding Society codes, and both show up constantly in weld inspection work — but they're built for different jobs, and using the wrong one isn't just a paperwork error. It can mean a weld that's actually out of spec.

What AWS D1.1 covers. D1.1, the Structural Welding Code – Steel, governs the design, procedures, qualification, fabrication, inspection, and repair of steel structures — tubes, plate, and structural shapes under static or cyclic loading. It's the code behind most structural steel fabrication, from buildings to industrial platforms, and it includes prequalified welding procedure specifications for common joint configurations, meaning many joints don't require separate procedure qualification testing.

D1.1 covers carbon and low-alloy structural steel. Thin sheet steel falls under AWS D1.3, and aluminum structures under AWS D1.2. The current edition is D1.1:2025.

What AWS D17.1 covers. D17.1, the Specification for Fusion Welding for Aerospace Applications, governs welding on aircraft and space hardware — aluminum-, nickel-, iron-, cobalt-, magnesium-, and titanium-based alloys joined by arc and high-energy beam processes. Unlike D1.1, D17.1 has no prequalified procedures: every combination of base metal, filler metal, joint design, and process has to be qualified through coupon testing before it's used in production. The current edition, D17.1/D17.1M:2024, is the fourth.

D17.1 Weld Classes: A, B, and C

D17.1 sorts every weld into a class based on what happens if it fails. The class sets both how much inspection the weld gets and which acceptance criteria apply:

• Class A — a joint whose failure under any operating condition would cause loss of the equipment or system, or of one of its major components
• Class B — a joint whose failure would reduce the overall strength of the equipment or system, or limit its intended function
• Class C — a joint whose failure wouldn't affect the performance of the equipment or system, and that needs no stress analysis

The class comes from engineering, usually on the drawing — it isn't something the welder or inspector chooses.

Why the acceptance criteria matter. The gap between the two codes shows up clearly in inspection. D17.1's radiographic and penetrant acceptance criteria are considerably tighter than D1.1's — a small indication that D1.1 would accept on a structural joint can be cause for rejection on a D17.1 Class A aerospace weld. Applying structural-steel tolerances to an aerospace part, or the reverse, isn't just imprecise — it can pass welds that shouldn't ship, or reject ones that are actually sound.

Side by Side

• Typical work: D1.1 — buildings, platforms, and other steel structures; D17.1 — aircraft and space hardware
• Materials: D1.1 — carbon and low-alloy steel; D17.1 — aluminum, nickel, iron, cobalt, magnesium, and titanium alloys
• Procedures: D1.1 — prequalified WPSs allowed for many joints; D17.1 — every procedure qualified by test
• Acceptance criteria: D1.1 — depend on the type of connection, whether it's statically or cyclically loaded, and the inspection method; D17.1 — depend on the weld class

How to Tell Which Code Applies

The contract documents decide, not the shop. Check the drawings, specifications, and purchase order — the engineer of record on a structural job, or the engineering authority on aerospace hardware, names the governing code and edition. If they don't, ask before welding starts, not after an inspection turns up a disagreement.

Knowing which code governs your weld — and inspecting to its specific procedure qualification and acceptance requirements — is the foundation of a defensible weld inspection program. Lion NDT's CWI services are built around exactly this: identifying the correct governing code for your structure and inspecting to it, whether that's a steel platform under D1.1 or an aerospace assembly under D17.1.