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. This guide follows the W59-18 edition (May 2018), which names CSA S6 and CSA S16 as examples of governing design standards.
Canadian context: CSA W59 works alongside CSA W47.1 (company certification). W59-18 Clause 3.1.1 requires contractors working under W59 to comply with CSA W47.1 when the contract or the governing design standard (for example, CSA S6 or CSA S16) mandates it. Companies apply for W47.1 certification to the Canadian Welding Bureau (CWB).
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 metals, 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). W59-18 names CSA S6 and CSA S16 as examples of a governing design standard that can mandate company certification (Clause 3.1.1).
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 when the contract or governing design standard mandates it.
This guide follows CSA W59-18, published May 2018. If your contract names another edition, check that edition's text. 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 W59-18 Clause 3.1.3.1 provides a prequalified path similar to D1.1 Clause 5. Joints for SMAW, SAW, FCAW, MCAW (spray transfer mode), GTAW, and GMAW (spray and pulse transfer mode) that conform to Clause 10 are deemed prequalified and approved without procedure qualification tests, provided the welding procedures also conform to Clauses 4, 5, and 10.
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 six processes listed in Clause 3.1.3.1: shielded metal arc welding (SMAW), submerged arc welding (SAW), flux-cored arc welding (FCAW), metal-cored arc welding (MCAW, spray transfer mode), gas tungsten arc welding (GTAW), or gas metal arc welding (GMAW, spray and pulse transfer mode). The joint must conform to Clause 10, and the welding procedure must also conform to Clauses 4, 5, and 10. The base metal must conform to the CSA or ASTM standards listed in Clauses 3.2.2 and 3.2.3, or to another specification of equivalent welding quality determined by the contractor's engineer and approved by the engineer (Clause 3.2.1). Preheat and interpass temperatures must meet the minimums of Table 5.3.
Joint details may depart from Clause 10 only if the contractor has the proposed joint and joint welding procedure qualified in accordance with the requirements of CSA W47.1 (Clause 3.1.3.2). For how D1.1 documents procedure qualification tests, see the procedure qualification record guide.
Base Metals and Steel Grades
CSA W59-18 lists permitted base metals in Clause 3.2: CSA G40.21 grades in Clause 3.2.2 and ASTM standards in Clause 3.2.3. For preheat, Table 5.3 lists each steel under specific columns, and the column headings add the welding process and the consumable's diffusible hydrogen designator. The primary steel grades covered include these CSA G40.21 designations:
- 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). W59-18 lists it as 300W (44W). In Table 5.3, 300W appears in Column 2 (consumables with diffusible hydrogen designators of ≤ H16, without a designator, or any non-low-hydrogen electrode) and in Column 3 (≤ H8 consumables, GMAW, GTAW).
- 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
- Higher-strength structural grades used in specialized applications where weight reduction or higher load capacity is required. Table 5.3 lists 400W and 480W in Column 4, whose minimum preheat and interpass temperatures are higher than Column 3's in each band over 20 mm, for example 65 °C instead of 10 °C over 20 mm to 40 mm.
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
W59-18 Table 5.3 sets minimum preheat and interpass temperatures by steel, thickness, and welding process. The column also depends on the consumable's diffusible hydrogen designator: Column 2 covers SMAW, FCAW, MCAW, and SAW with ≤ H16, no designator, or a non-low-hydrogen electrode; Columns 3 and 4 share the ≤ H8, GMAW, GTAW heading and split by steel; Column 5 (≤ H4) covers only the steels listed under it.
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 W59-18 Clause 3.1.2.1 requires filler metals and allied materials to conform to CSA W48, except for stud welding. W59 writes the SMAW classification as E4918 (E7018) in Clauses W.9.2.5 and W.9.3, and its informative Annex V cross-references W48-01 ER49S-6 to the former imperial designation ER70S-6. The matching requirements ensure that filler metal strength and composition suit 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: D1.1 in Clause 5, and W59-18 in Clause 3.1.3 with the joint details of Clause 10. 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 when the contract or governing design standard mandates it. 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 list the base metals they accept, 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 when the contract or governing design standard mandates it (Clause 3.1.1). 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 3.1.3, Clause 10 joints) | Yes (Clause 5) | No |
| Base metal grouping | Table 5.3 columns by steel, process, and hydrogen designator | Table 5.6 groups (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 when mandated (Clause 3.1.1) | 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 carbon and low-alloy steel structures. W59-18 names CSA S6 and CSA S16 as examples of a governing design standard (Clause 3.1.1). 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. Under CSA W59-18 Clause 3.1.3.1, joints for SMAW, SAW, FCAW, MCAW (spray transfer mode), GTAW, and GMAW (spray and pulse transfer mode) that conform to Clause 10 are deemed prequalified and approved without procedure qualification tests, provided the welding procedures also conform to Clauses 4, 5, and 10. A joint detail that departs from Clause 10 needs the joint and joint welding procedure qualified in accordance with CSA W47.1 (Clause 3.1.3.2).
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 the certification of companies for fusion welding of steel, while CSA W59 specifies the technical requirements for welded steel construction. W59-18 Clause 3.1.1 requires contractors to comply with CSA W47.1 when the contract or the governing design standard (for example, CSA S6 or CSA S16) mandates it. In the W47.1-03 edition (Clause 5.2), the Division reflects the company's welding engineer: Division 1 employs one full-time, Division 2 retains one part-time, and Division 3 is not required to employ or retain one. There is no equivalent company certification requirement in AWS D1.1.