Specs often say “weld per AWS” and stop, or cite D1.1 on a 14-gauge cabinet where it does not strictly apply. The AWS D1 family is divided by material and thickness, and citing the right code decides which joints are prequalified, how welders are qualified and what the inspector checks. Here is which code applies to what.
Need this built to your spec? Call 601.892.5017 or email collin.t@fabtekindustries.com — send the drawing and we’ll quote it.
- AWS D1.1 — Structural Welding Code, Steel: carbon and low-alloy steel 1/8″ (3 mm) and thicker. Substation structures, tanks, frames, bases, skids.
- AWS D1.3 — Sheet Steel: carbon steel 3/16″ (0.188″) and thinner. Enclosures, cabinets, panels, housings.
- AWS D1.6 — Stainless Steel; AWS D1.2 — Aluminum; D1.8 — seismic supplement to D1.1. Some tank OEMs specify ASME Section IX instead.
- What Gauge Steel for a NEMA 3R Walk-In Enclosure?
- ASTM A123 vs. A153: Which Galvanizing Spec Applies?
- Minimum Bend Radius for 5052 Aluminum Sheet
- Powder Coat Film Thickness for Outdoor Electrical Enclosures
- IEEE 2000-Hour Salt Spray: What the Rating Actually Means
- AWS D1.1 vs. D1.3 vs. D1.6: Which Welding Code Applies? (you are here)
- Bolt-Hole Tolerances for Substation Steel Structures
- Non-Segregated Bus Duct: Ampacity, Bar Size and Housing
- Material Certs and Heat Numbers: What Traceability Means
- How to Spec Anchor-Bolt Patterns for Equipment Stands
The answer
Structural steel gets D1.1. Sheet steel gets D1.3. Stainless gets D1.6. Aluminum gets D1.2. AWS D1.1/D1.1M, Structural Welding Code — Steel, applies to welded carbon and low-alloy steel structures with base metal 1/8″ (3 mm) and thicker: substation and transmission structures, transformer tanks, equipment skids, mezzanines, generator bases. AWS D1.3/D1.3M, Structural Welding Code — Sheet Steel, applies to carbon steel 0.188″ (3/16″) and thinner: enclosures, cabinets, panels and bus duct housings in 11- to 18-gauge. AWS D1.6 covers stainless steel of all thicknesses; D1.2 covers aluminum; D1.8 supplements D1.1 for seismic-force-resisting systems. FabTek qualifies welders and procedures to D1.1 and D1.3 for its carbon-steel work and to D1.6 for stainless; see Quality & Compliance.
Code by product
| AWS D1.1 — Structural Steel | ≥ 1/8″ carbon & low-alloy steel. Dead-ends, bus supports, equipment stands, tanks, skids, platforms, bases, mezzanine steel. Prequalified joints, CJP/PJP groove and fillet welds, NDE provisions, welder qualification by thickness and position. |
|---|---|
| AWS D1.3 — Sheet Steel | ≤ 3/16″ carbon steel (sheet, and sheet-to-structural connections). Enclosures, cabinets, doors, panels, housings, brackets. Arc-spot and arc-seam welds, fillet and flare welds in sheet; welder qualification for thin material. |
| AWS D1.6 — Stainless Steel | Austenitic, ferritic, duplex stainless in all thicknesses. NEMA 4X enclosures, stainless bus duct housings, process equipment, CDU frames. |
| AWS D1.2 — Aluminum | Aluminum structures and sheet. Aluminum bus duct housings, enclosures, heat sinks and frames. |
| AWS D1.8 — Seismic Supplement | Used with D1.1 for demand-critical welds in seismic-force-resisting systems. |
| ASME BPVC Section IX | Pressure-vessel welding qualification; specified by some transformer OEMs for tanks in lieu of or alongside D1.1. |
| AWS D9.1 | Sheet metal (HVAC duct, non-structural); not for electrical enclosures. |
The D1.1 / D1.3 overlap
Between 1/8″ and 3/16″ both codes can apply, and many enclosure products live there: 11-gauge (0.120″) doors and 10-gauge (0.135″) frames on a walk-in, or a 3/16″ base channel welded to a 12-gauge skin. The designer picks. D1.3 is written for sheet and its joint types and welder qualifications suit thin material; D1.1 is the more conservative choice and is what most utility and owner specs default to. Where sheet is welded to structural members (a cabinet body to its base channel), D1.3 explicitly covers sheet-to-structural connections. A clear spec states the code per component or states “D1.1 for members ≥ 1/8″, D1.3 for sheet < 1/8″” and lets the fabricator apply both.
WPS, PQR and welder qualification
- WPS (Welding Procedure Specification) — the written recipe for a joint: process, base and filler metals, position, preheat, parameters, technique. Every production weld follows a WPS.
- PQR (Procedure Qualification Record) — the test record proving the WPS produces sound welds, by welding and testing coupons. D1.1 allows many prequalified joints that need a WPS but no PQR when the code’s conditions are met; non-prequalified joints and unusual materials require a PQR.
- WPQ (Welder Performance Qualification) — the individual welder’s test, by process, position and thickness range, with a continuity requirement (welding within a set interval, typically six months, to remain qualified).
- Inspection — visual acceptance criteria are in each code; NDE (MT, UT, RT, PT) is applied where the design or owner specifies. Inspector qualification (CWI) is often required by the owner.
What the paperwork looks like and why buyers audit it is in ISO 9001 and AWS-Certified Welds.
How to write it
“Welding of structural members 1/8″ and thicker shall conform to AWS D1.1/D1.1M; welding of sheet steel 3/16″ and thinner shall conform to AWS D1.3/D1.3M; stainless steel per AWS D1.6/D1.6M. Fabricator shall maintain WPSs and supporting PQRs for all joints and shall furnish welder qualification records on request. Visual inspection per the applicable code; [MT/UT] on [designated welds] per the drawings.” Name the code per material; do not write “AWS certified” and stop — AWS certifies welders and inspectors, and codes govern the work.
How FabTek handles it: Structural steel and tanks are welded to D1.1 and sheet-metal enclosures to D1.3 by welders qualified to each, with WPSs and PQRs on file, weld maps for structural designs, and visual and NDE inspection recorded by piece mark. If your drawing calls for something different, send it — we build to print. Request a quote.
Frequently asked questions
What thickness does AWS D1.1 cover?
AWS D1.1, Structural Welding Code — Steel, covers carbon and low-alloy steel with base metal 1/8 in. (3 mm) and thicker: substation structures, transformer tanks, skids, platforms and frames. Sheet steel 3/16 in. and thinner is covered by AWS D1.3.
Which welding code applies to electrical enclosures and cabinets?
AWS D1.3, Structural Welding Code — Sheet Steel, for carbon steel 3/16 in. and thinner, including sheet-to-structural connections. Stainless enclosures fall under D1.6 and aluminum under D1.2. Components 1/8 in. and thicker, such as base channels, may be specified to D1.1.
What is the difference between a WPS and a PQR?
A WPS (Welding Procedure Specification) is the written procedure for making a weld — process, materials, position, parameters. A PQR (Procedure Qualification Record) is the test record proving that procedure produces sound welds. D1.1 prequalified joints need a WPS but no PQR when code conditions are met.
