CSA W59: The Structural Welding Code in Canada

The structural welding code in Canada is CSA W59, "Welded steel construction (metal arc welding)." It sets the requirements for welded carbon and low-alloy steel construction: the design of welded connections, electrodes and consumables, base metals, workmanship, inspection, quality levels and stud welding. The current edition was published in 2024. W59 doesn't stand alone. It works with CSA S16 for steel design and CSA W47.1 for company certification, and that chain is how structural welding is regulated in Ontario.

How W59 fits into the building code

The Ontario Building Code doesn't mention W59 by name. The connection runs through the steel design standard:

1. The 2024 Ontario Building Code requires structural steel to be designed to CSA S16 and references the 2019 edition, CSA S16-19.
2. CSA S16 brings in the welding standards: welded construction to CSA W59, and certification of fabricators and erectors who weld to CSA W47.1 (Division 1 or 2), CSA W55.3, or both.
3. The project specification usually repeats these requirements and may add inspection and testing on top.

So when an engineer specifies structural steel to S16, the welds on it are expected to meet W59, made by a company certified by the Canadian Welding Bureau. Our overview of Canadian structural steel codes shows where the other standards fit.

Which edition applies?

Standards are revised more often than building codes are adopted. A newer W59 edition can be on the shelf while an older one is called up by the design standard a project uses. The practical rule is the same as for S16: the edition that governs is the one referenced through the code and specification for that project. Your engineer of record decides, and certified fabricators follow the edition their procedures are approved to. If a specification names an edition, work to it.

What CSA W59 covers

W59 is a long technical standard, but its content falls into a few areas.

Prequalified and qualified procedures

One idea from W59 worth knowing is prequalification. Common joint details and processes that have a proven track record are prequalified, so a certified company can use them without separate procedure testing, provided it stays within the limits set out for them. Joints, processes or materials outside those limits need their procedures qualified by testing.

Either way, a CWB-certified company submits its welding procedures to the CWB Group for review and approval. On the shop floor, welders work from welding procedure data sheets that state the process, consumable, joint, position and parameters for each weld.

Workmanship

Workmanship requirements are where W59 reaches the shop floor: how joints are prepared and fitted, when steel has to be preheated (which depends on the steel, its thickness and the process), acceptable weld profiles, and how defects are removed and repaired. These values are applied by the welding supervisor and built into the procedures. They are not something to look up and apply from a summary.

The family of CSA welding standards

W59 is one of several CSA welding standards used on Canadian construction projects:

• CSA W59: welded steel construction. The structural welding code.
• CSA W59.2: welded aluminum construction.
• CSA W47.1: certification of companies for fusion welding of steel. See CSA W47.1 and CWB company certification.
• CSA W47.2: certification of companies for fusion welding of aluminum.
• CSA W48: filler metals and allied materials for metal arc welding.
• CSA W178.1: certification of welding inspection organizations.
• CSA W178.2: certification of welding inspectors.
• CSA W186: welding of reinforcing bars in reinforced concrete construction, which only applies to bar grades meant to be welded.

The short version: W59 tells you how to make the weld, W47.1 tells you who is allowed to make it, W48 covers what goes into it, and W178 covers who inspects it.

Who uses W59 day to day

In a certified shop, W59 isn't a book on a shelf. Different people apply different parts of it:

• The welding engineer (in Division 1 and 2 companies) is responsible for the company's welding procedures and for engineering questions such as non-standard joints and repairs.
• The welding supervisor makes sure the work on the floor follows the approved procedures and the workmanship requirements.
• Welders work from the welding procedure data sheets for the joint in front of them, within the processes and positions they're qualified for.
• Inspectors, from the shop's quality control or an outside inspection organization, check the finished welds against the inspection and quality requirements.
• Detailers show the weld types and sizes from the design on the shop drawings, using standard welding symbols.

CSA W59 vs AWS D1.1

Search for "structural welding code" and most results point to AWS D1.1, the American Welding Society's structural welding code for steel. It is the US counterpart to W59 and is used widely in the United States.

The two documents cover similar technical ground, and both use the idea of prequalified procedures. The differences that matter in practice:

• Which code the design relies on. CSA S16 calls up W59. A Canadian building designed to S16 normally expects W59 and CWB certification, not D1.1 and US certification.
• Certification system. In Canada, W59 works together with mandatory company certification under CSA W47.1, administered by the CWB Group. The US system is organized differently.
• Units and designations. W59 works in metric and Canadian material standards such as CSA G40.21.

If steel for a Canadian project is being fabricated outside Canada, check with the engineer of record before ordering. We compare the two systems in CWB vs AWS certification.

What W59 means for contractors and owners

You don't need to read W59 to buy structural steel. You do need to make sure the people welding your steel work to it:

• Hire a certified company. CWB certification to CSA W47.1 means the company's procedures, supervisors and welders are set up to meet W59.
• Read the specification. It will name the welding standards and any inspection or testing requirements beyond visual inspection.
• Plan field welds. If welds are made on site, the erector needs the same certification, and the welds need access and weather protection.
• Keep the paperwork. Welding procedure data sheets, welder qualifications and inspection reports may be needed for submittals or the building file.
• Leave design to the engineer. Weld sizes and connection details come from the structural design or the connection engineer, not from the shop floor.

For how W59 fits with fabrication and erection tolerances and the other shop standards, see steel fabrication standards in Canada. For the practical side of shop and site welding, see structural welding services.

Welded to the standard at Procut

Our shop welding is certified by the Canadian Welding Bureau, and every structural piece we fabricate is cut, fitted, welded and marked to match the shop drawings we prepare in-house. If your specification names a W59 edition, a certification division or inspection requirements, include it with your drawings and we'll confirm what we can provide.

Request a quote with your drawings, or see our fabrication and welding services.