Structural Welding Codes (AWS D1.1 Overview)

AWS D1.1, the Structural Welding Code - Steel, is the rulebook for most welded steel structures in North America. It decides which joints you may use, who may weld them, and what an inspector will accept. You do not need to memorize it, but you need to know how it is organized and how it reaches your work. This guide is a map of the code. Your job's contract documents and your copy of the current edition are always the final word.

What You Will Be Able to Do

• Say what D1.1 covers and what it leaves to other codes.
• Find the right part of the code by topic.
• Explain prequalified joints and read a joint designation.
• Work out what a D1.1 welder test covers.
• Name the field conditions and acceptance limits that affect your welds.

What D1.1 Covers

D1.1 covers welded structures made from carbon and low-alloy steels, statically or cyclically loaded, with a base metal 1/8 inch or thicker. That includes building frames, stairs and platforms, towers, and many equipment frames.

It does not cover pressure vessels or pressure piping. Those fall under ASME and other codes.

AISC 360 is a design specification, not a welding code. A structural engineer designs to it, and it sends the fabricator to D1.1 for how the welding gets done.

Which Edition Applies

D1.1 is revised every few years. The current edition at the time of writing is AWS D1.1/D1.1M:2025. The contract documents can name an older edition, and in that case, that edition governs your job. Clause and table numbers change between editions, so a number that a coworker quotes from memory may be out of date.

Since the 2020 edition, the main clauses run like this:

Older editions used a different order, so check the table of contents. In the 2015 edition, for example, the visual acceptance table was Table 6.1. It is now Table 8.1.

Static and Cyclic Loading

D1.1 sorts structures by how they are loaded.

• Statically loaded means the load stays fairly steady, as in most building frames.
• Cyclically loaded means the load repeats, as in crane runways and some bridges and supports. Repeated loads cause fatigue, which is cracking that grows a little with each cycle.

Cyclic work has tighter limits on flaws such as undercut, because a small notch can start a fatigue crack. Find out which one applies to your job before you judge a weld.

Prequalified or Qualified by Test

Every code weld needs a written Welding Procedure Specification (WPS). D1.1 gives you two routes to one.

A prequalified WPS stays inside the limits in Clause 5: listed base metals, filler metals, processes and joint details. No procedure test is needed because the code accepts those combinations from long experience. The WPS must still be written and followed, and welders must still be qualified. Common prequalified processes are SMAW, SAW, GMAW (not short-circuit transfer) and FCAW.

A WPS qualified by test is needed for anything outside those limits. Test results go on a Procedure Qualification Record, and Clause 6 lists the variables that trigger requalifying.

Reading a Joint Designation

Prequalified joints have short names in the code's figures. Here is how to read B-U2a:

Other groove numbers include 1 for square, 3 for double-V, 4 for single-bevel and 5 for double-bevel. The figure for each joint gives the allowed process, thickness, root opening, groove angle and positions. It also gives tolerances, listed separately for "as detailed" (what is cut) and "as fit-up" (what you find when the parts come together).

A typical single-V setup has a 60 degree included angle, a 1/8 inch root opening and a land of 1/16 to 1/8 inch. Always read the actual figure, because small tolerances on the root opening and groove angle apply. If the fit is out of tolerance, stop. Fix it or get engineering approval before you weld.

Welder Qualification Under D1.1

Your test decides what you may weld. In the D1.1 position table, groove tests generally cover the following.

The test also limits thickness. A test on 3/8 inch plate generally qualifies you for 1/8 to 3/4 inch, and a test on 1 inch plate qualifies you for 1/8 inch and up. Some tests are by process, and a qualification with one process does not carry over to another.

Your qualification lasts indefinitely, as long as you keep using the process. If you go more than six months without welding in that process, it expires, and you must requalify. Shops track this in a welder continuity log. Your employer has to keep your records, and an inspector can ask for a retest if there is a specific reason to question your work.

Preheat and Interpass

D1.1 requires minimum preheat based on the steel, the thickness and the type of filler. Preheat slows cooling, so hydrogen can escape and less hard metal forms next to the weld. The prequalified table sorts steels into categories. On a common grade such as A36 with low-hydrogen filler, earlier tables ran from no preheat on thin plate up to about 225 F on plate over 2-1/2 inches. Use the table in your edition.

Two rules apply on almost every job:

• If the steel is below 32 F, heat it to at least 70 F, and keep it there while you weld.
• Keep the interpass temperature above the minimum. A WPS often sets a maximum too, commonly about 550 F on standard carbon steel.

Tacks and Temporary Welds

Tacks that stay in the joint are part of the weld. They must be made by qualified welders, with suitable filler, and they must meet the same quality rules. If a tack cracks, remove it. Tack welds that won't be incorporated into the final weld must be removed, unless the engineer allows them to stay. The same is true of temporary attachments such as erection aids. Check the surface afterward for cracks and gouges.

Field Conditions

Outdoor welding has limits of its own. Under D1.1:

• Do not weld when the surfaces are wet or exposed to rain or snow.
• Do not weld when the ambient temperature is below 0 F, unless you have a heated enclosure.
• Gas-shielded welding needs protection from winds above 5 miles an hour. Windscreens and tents are normal in the field.
• Keep low-hydrogen electrodes in an oven at the site, and watch their time out of the oven. E7018 is the most common rod for this work.

Check your own edition, as well as the job's rules, before you decide conditions are fine.

What an Inspector Accepts

D1.1 sets a visual acceptance table for finished welds. Here is a summary of the common limits from recent editions. Your edition and contract documents are the final word.

Rejected welds are repaired under an approved procedure, and the repair gets inspected too.

Interpass Cleaning and Good Practice

Between passes, chip all slag, brush off oxide and grind out any flaws. A clean surface lets the next pass fuse properly and stops slag from being buried. Use the sequence on the WPS, and balance your welds across the member to limit distortion. A long beam that bows from careless sequencing can fail its dimensional tolerance even if every weld is sound.

Your Responsibilities

1. Know your WPS and keep it at your station.
2. Stay inside the parameter ranges.
3. Use only the filler the WPS lists.
4. Mark your welds with your stamp if your shop requires it.
5. Speak up when the fit-up is wrong.
6. Keep your qualification current.

Common Mistakes

• Quoting clause numbers from memory. Numbering changes between editions.
• Calling a job "prequalified" after changing a variable. One change outside the limits ends it.
• Assuming every structure is statically loaded. Cyclic work has tighter limits.
• Treating tacks as temporary. Tacks that stay in must meet the same quality rules.
• Welding on wet steel in the field. Moisture adds hydrogen and leads to cracking.

Check Your Understanding

A customer asks you to weld a pressure vessel nozzle "to D1.1." Why should you question this?

D1.1 does not cover pressure vessels. Those usually fall under the ASME code, so ask which code really governs.

A WPS calls for joint B-U4a. What can you tell from the name?

It is a butt joint, unlimited in thickness, with a single-bevel groove, and it is a variant labeled a. The figure gives the details.

You passed 3G and 4G on 3/8 inch plate. A job calls for an overhead weld on 1-1/2 inch plate. Are you covered?

The position is covered, but the thickness may not be. A 3/8 inch test generally stops at 3/4 inch, so check your record.

It is 25 F, and the steel is cold but dry. The WPS shows no preheat for this thickness. What should you do?

Under D1.1, steel below 32 F has to be heated to at least 70 F and held there while you weld. Check your edition and your WPS, then heat it.

Key Takeaways

• D1.1 covers structural carbon and low-alloy steel, 1/8 inch and thicker, and not pressure vessels or piping.
• The contract names the edition. Clause numbers change between editions.
• A prequalified WPS needs no test, but only if everything stays inside the limits.
• Your test sets your positions and thickness, and six months without the process can end it.
• Cracks are never accepted, and cyclic work has tighter limits.
• Bad fit-up and bad weather are reasons to stop and ask.