CSA W59 — Welded Steel Construction (Canadian Standard)
CSA W59 is the Canadian Standards Association standard for welded steel construction. It establishes requirements for welding design, procedure qualification, fabrication, and inspection of structural steel in Canada, referenced by the National Building Code through CSA S16, making compliance mandatory for all structural welding in Canadian provinces.
Canadian context: CSA W59 works alongside CSA W47.1 (company certification). In Canada, a fabrication shop must hold W47.1 certification from the Canadian Welding Bureau (CWB) and follow W59 technical requirements. AWS D1.1 is not accepted as a substitute for CSA W59 in Canadian building code jurisdictions.
What Is CSA W59?
CSA W59 is the Canadian standard for welded steel construction, equivalent in scope to AWS D1.1 in the United States. It covers structural steel fabrication and erection requirements including welding procedures, prequalification, base metal groups, preheat, and filler metal matching. CSA W59 uses metric units (MPa, mm, degrees Celsius).
CSA W59 — formally titled “Welded Steel Construction” — is the Canadian national standard governing the welding of structural steel. It covers the design of welded connections, qualification of welding procedures, qualification of welders and welding operators, fabrication requirements, and inspection criteria. The standard is published by the Canadian Standards Association (CSA Group) and is referenced by CSA S16, the Canadian standard for design of steel structures, which in turn is referenced by the National Building Code of Canada (NBCC).
CSA W59 shares a similar organizational structure with AWS D1.1 and is often described as the Canadian equivalent of D1.1. Both standards provide prequalified and non-prequalified WPS paths, both specify preheat requirements by material grade and thickness, and both use similar acceptance criteria for visual and nondestructive inspection. However, CSA W59 references Canadian steel grades (CSA G40.20/G40.21), Canadian filler metal standards (CSA W48), and requires company certification under CSA W47.1.
The current edition is CSA W59:2018. The standard applies to the welding of carbon and low-alloy steels with a specified minimum yield point or yield strength not exceeding 700 MPa. It does not cover pressure vessel or pipeline welding, which fall under ASME Section IX and API 1104 respectively.
Prequalified WPSs Under CSA W59
CSA W59 Clause 5 provides a prequalified path similar to D1.1 Clause 5. WPSs that meet all requirements are exempt from qualification testing. Prequalified processes include SMAW with low-hydrogen electrodes, GMAW (except short-circuit), FCAW, and SAW. The fabricator documents compliance but does not produce test welds.
Like D1.1, CSA W59 provides a prequalified path for welding procedures that meet specific conditions. A prequalified WPS must satisfy all of the following requirements to avoid the need for procedure qualification testing:
The welding process must be one of the four prequalified processes: shielded metal arc welding (SMAW), submerged arc welding (SAW), gas metal arc welding (GMAW, except short-circuit transfer), or flux-cored arc welding (FCAW). The base metal must be listed in the approved base metal tables. The filler metal must match the base metal per the filler metal compatibility tables. The joint configuration must match one of the prequalified joint details in the standard. Preheat and interpass temperatures must meet the minimum values specified in the preheat tables.
When any element falls outside the prequalified limits, the procedure must be qualified by testing. The qualification process requires producing test coupons, performing destructive tests (tension, bend, and macro-etch), and documenting the results on a procedure qualification record.
Base Metal Groups and Steel Grades
CSA W59 organizes base metals into groups based on chemical composition, mechanical properties, and weldability characteristics. Each group defines the range of permitted steel grades, preheat requirements, and compatible filler metals. The primary steel grades covered include CSA G40.20/G40.21 designations commonly used in Canadian structural and bridge fabrication:
- 300W
- General structural steel with 300 MPa (44 ksi) minimum yield strength per CSA G40.21. The W suffix indicates weldable grade. Strength-wise, 300W sits between ASTM A36 (250 MPa / 36 ksi yield) and A572 Gr.50 (345 MPa / 50 ksi yield), roughly comparable to ASTM A572 Gr.44. This is the most common structural steel grade in Canadian fabrication and falls in the lowest preheat category for most thicknesses.
- 350W and 350WT
- Higher-strength structural steel at 350 MPa minimum yield. 350WT includes Charpy V-notch toughness requirements for low-temperature service. Comparable to ASTM A572 Gr.50. Preheat requirements increase with thickness, similar to D1.1 Category B behavior.
- 400W and 480W
- High-strength structural grades requiring higher preheat minimums and more restrictive heat input control. These grades are used in specialized applications where weight reduction or higher load capacity is required. Fabricators working with 400W and 480W steel should expect higher preheat temperatures and more restrictive interpass temperature limits.
CSA W59 also accepts ASTM-designated steels listed in its base metal compatibility tables. Canadian fabricators working on projects with ASTM-specified steel can use the W59 tables to determine preheat requirements and filler metal matching, provided the specific grade is listed.
Preheat Requirements
CSA W59 preheat tables specify minimum preheat and interpass temperatures based on base metal grade, material thickness, and welding process. The tables use metric units (Celsius and millimeters). Preheat requirements generally increase with material thickness and carbon equivalent. Low-hydrogen processes (SMAW with E49018 or equivalent low-hydrogen electrodes, SAW, GMAW, FCAW with gas shielding) qualify for lower preheat temperatures than non-low-hydrogen processes.
The preheat philosophy mirrors D1.1 Table 5.11 — the objective is to slow the cooling rate in the heat-affected zone, allowing hydrogen to diffuse out before the weld cools to temperatures where hydrogen cracking can initiate. The specific temperature values may differ from D1.1 due to the different steel grade designations and the metric units used in CSA W59.
Filler Metal Requirements
CSA W59 references CSA W48 for filler metal classifications. CSA W48 classifications parallel the AWS A5 series but use Canadian designations. Common equivalencies include E49018 (CSA) corresponding to E7018 (AWS), E4914 (CSA) corresponding to E7014 (AWS), and ER49S-6 (CSA) corresponding to ER70S-6 (AWS). The matching requirements ensure that the filler metal strength and composition are appropriate for the base metal being welded.
Fabricators importing AWS-classified consumables for use under CSA W59 should verify that the specific AWS classification is listed in the W59 filler metal compatibility tables. Most common AWS A5.1, A5.5, A5.17, A5.18, A5.20, and A5.29 classifications have corresponding acceptance in CSA W59, but verification is required for each specific classification.
How CSA W59 Compares to Other Standards
CSA W59 governs Canadian structural steel; D1.1 governs U.S. structural steel. Both provide prequalified WPS paths under their respective Clause 5. Key differences: W59 uses metric units, references CSA G40.21 steel grades and CSA W48 filler metals, and requires company certification under CSA W47.1. D1.1 uses imperial/metric dual units and AWS A5.x filler metals.
CSA W59 vs AWS D1.1
The standards are structurally similar — both provide prequalified WPS paths, both organize base metals into groups, and both have comparable acceptance criteria for weld discontinuities. The primary differences are jurisdictional: W59 references Canadian steel grades (G40.20/G40.21), Canadian filler metal specifications (W48), uses metric units, and requires CSA W47.1 company certification. A WPS qualified under D1.1 cannot be used for CSA W59 work without re-qualification or documentation showing compliance with W59 provisions.
CSA W59 vs ASME Section IX
CSA W59 applies to structural steel construction, while ASME IX applies to pressure equipment. For Canadian pressure vessel and piping work, ASME IX governs welding qualification, not CSA W59. Many Canadian fabrication shops maintain both W59 certification (through CWB/W47.1) and ASME IX qualifications for pressure work. The two standards use completely different base metal grouping systems, variable classifications, and qualification frameworks.
| Aspect | CSA W59 | AWS D1.1 | ASME IX |
|---|---|---|---|
| Scope | Structural steel (Canada) | Structural steel (US) | Pressure equipment |
| Units | Metric (MPa, mm, °C) | Imperial + metric dual | Imperial + metric dual |
| Prequalified WPS? | Yes (Clause 5) | Yes (Clause 5) | No |
| Base metal grouping | 4 grade groups | Table 5.6 categories (I–V) | P-numbers |
| Filler metal reference | CSA W48 | AWS A5.x | F-numbers |
| Preheat method | Table 5.3 | Table 5.11 | Per WPS/PQR |
| Company certification | W47.1 required | Not required | ASME stamps |
Related Standards Guides
Frequently Asked Questions
CSA W59 is the Canadian Standards Association standard for welded steel construction. It establishes requirements for the design, qualification, fabrication, and inspection of welded steel structures in Canada. CSA W59 is referenced by the National Building Code of Canada (NBCC) through CSA S16 (Design of Steel Structures), making it the mandatory welding standard for structural steel in all Canadian provinces and territories. The standard covers prequalified and non-prequalified joint configurations, preheat requirements, filler metal selection, and inspection criteria.
CSA W59 is the Canadian equivalent of AWS D1.1. Both standards cover structural steel welding and share a similar structure with prequalified and qualified WPS paths. Key differences include base metal groupings (CSA W59 references CSA G40.20/G40.21 steel grades like 300W and 350W rather than ASTM designations), filler metal specifications (CSA W48 versus AWS A5 series), and preheat tables that use Celsius and millimeters. CSA W59 also references CSA W47.1 for company certification requirements, which has no direct D1.1 equivalent. Many provisions are technically harmonized between the two standards.
Yes. Like AWS D1.1, CSA W59 provides a prequalified path for welding procedures that meet specific conditions. Prequalified WPSs must use approved welding processes (SMAW, SAW, GMAW except short-circuit, or FCAW), base metals listed in the approved tables, matching filler metals, and joint configurations from the prequalified joint detail figures. Prequalified WPSs do not require procedure qualification testing. Non-prequalified procedures must be qualified by testing, similar to D1.1 Clause 6 requirements.
CSA W59 covers structural steel grades specified in CSA G40.20/G40.21, including 300W (300 MPa yield, between ASTM A36 and A572 Gr.50), 350W (similar to A572 Gr.50), 350WT (with Charpy V-notch toughness requirements), 400W, and 480W. The standard also accepts ASTM-designated steels that are listed in its base metal tables. Preheat requirements vary by steel grade, thickness, and welding process, similar to D1.1 Table 5.11 but organized by CSA grade designations and using metric units.
CSA W47.1 governs company certification for welding, while CSA W59 specifies the technical requirements for welded steel construction. In Canada, fabricators performing structural welding must hold CSA W47.1 certification, which requires documented quality systems, qualified welding procedures per W59, qualified welders, and periodic audits by the Canadian Welding Bureau (CWB). CSA W47.1 Division 1 covers steel, Division 2 covers aluminum, and Division 3 covers reinforcing steel. There is no equivalent company certification requirement in AWS D1.1.