AWS D1.1 versus the European standards: the key differences

AWS D1.1, the Structural Welding Code for steel published by the American Welding Society, is the governing standard for welded steel structures in the United States. Europe uses a set of separate standards instead: EN 1090-2 for execution, EN ISO 15614-1 for welding procedure qualification and ISO 9606-1 for welder qualification. Fabricators in the Netherlands working for American clients or on offshore projects will sooner or later meet AWS D1.1 alongside, or instead of, those European standards.

The differences go beyond numbering. AWS D1.1 is a single integrated document covering design, qualification, fabrication and inspection, and it allows prequalified procedures that can be used without a test coupon. This article compares both systems, explains what a prequalified WPS is and is not, and sets out what to watch when a project combines the two.

1. How AWS D1.1 is structured compared with European standards

AWS D1.1 is a code: one book covering the full life of a welded steel structure. It deals with the design of welded connections, prequalification of procedures, qualification by testing of procedures and welders, fabrication, inspection, stud welding, tubular structures and the strengthening and repair of existing structures. It applies to carbon and low-alloy structural steel, with separate codes for stainless steel, aluminium and sheet steel: AWS D1.6, D1.2 and D1.3.

In Europe the same ground is covered by standards that refer to one another:

• EN 1090-2 for the execution of steel structures, with execution classes EXC1 to EXC4.
• EN ISO 15614-1 for procedure qualification by testing, recorded in a WPQR.
• ISO 9606-1 for welders and ISO 14732 for welding operators.
• ISO 3834 for welding quality requirements and ISO 5817 for the acceptance of imperfections.

Design sits under Eurocode 3 rather than a welding standard, which makes the system modular but harder to oversee.

2. Prequalified WPSs: welding without a test coupon

The biggest practical difference is prequalification. AWS D1.1 lets you write a WPS without a procedure qualification record (PQR), provided you stay within every condition of the code:

• Only SMAW, SAW, GMAW (excluding short-circuit transfer) and FCAW are eligible.
• Base and filler metals must appear in the code's lists and be correctly matched.
• The joint must match a prequalified joint detail, including groove angle, root opening and tolerances.
• Preheat, welding position, bead sequence and layer thickness are fixed.

A prequalified WPS is not a free pass. It must still be written down, and any deviation means qualification by testing. Watch the material in particular: European grades such as S355 are not on the list of prequalified base metals, so European steel will normally require qualification by testing.

EN 1090-2 has no prequalification in this form. Alternative routes to EN ISO 15614-1 exist, such as previous welding experience or a standard welding procedure, but their use is limited by execution class.

3. Welders and inspection: different rules, different paperwork

A welder qualification under AWS D1.1 remains valid as long as the welder keeps using the process without a break of more than six months, unless there is a specific reason to question their ability. ISO 9606-1 requires six-monthly confirmation by the welding coordinator, plus periodic revalidation by retest or documented quality records. Ranges for thickness, diameter and position are built differently, so an ISO 9606-1 certificate does not automatically cover AWS work, or the other way round.

For inspection, AWS D1.1 has its own acceptance criteria for visual, ultrasonic and radiographic testing, distinguishing statically and cyclically loaded connections. In Europe welds are assessed against the ISO 5817 quality levels, linked to the execution class. American specifications often call for an AWS Certified Welding Inspector, whereas ISO 9712 is the European basis for NDT personnel.

4. When you meet AWS D1.1 in the Netherlands

AWS D1.1 is not everyday fare in Dutch steel construction, but it appears in recognisable situations:

• American clients and engineering contractors applying their own standard specifications, for example in the process industry.
• Offshore projects, where operator specifications call for AWS D1.1 alongside or instead of standards such as ISO 19902 or NORSOK M-101.
• Exports to the United States, where the client or local regulations expect AWS D1.1.

Importantly, AWS D1.1 does not replace EN 1090 for structures placed on the EU market. A load-bearing structure for a building or civil work in the EU falls under the Construction Products Regulation and needs CE marking to EN 1090-1. AWS D1.1 then comes on top as a contractual requirement.

5. Projects combining AWS D1.1 and EN standards

The trickiest case is a Dutch fabricator holding EN 1090 certification that must weld to an American specification. Points to watch:

• Agree up front which code governs procedures, welder qualification, acceptance criteria and inspection. Mixing them topic by topic leads to disputes at handover.
• Review existing WPQRs. A WPQR to EN ISO 15614-1 is formally not an AWS D1.1 PQR. If the client accepts it anyway, get that in writing.
• Plan for extra qualifications. Test coupons, testing and certification take weeks.
• Mind the units. AWS often works in inches and Fahrenheit, and a conversion error in a preheat temperature is easily made.

For the European side, our article on EN 1090-2 execution classes is a good starting point. If American specifications come up regularly, a standing set of AWS qualifications next to your European WPQRs pays off. Targeted EN 1090 support puts the European foundation in order so AWS requirements can be added in a controlled way.