Look up the minimum preheat and interpass temperature for welded steel construction per CSA W59:2018 Table 5.3. Select your steel grade group, welding process, hydrogen designator, and material thickness to find the required preheat for Canadian structural welding projects.
Select the steel grade group, welding process and hydrogen designator, and enter the material thickness. CSA W59 Table 5.3 organizes preheat into four columns based on process type and diffusible hydrogen content.
CSA W59:2018 Table 5.3 specifies minimum preheat for four process/hydrogen columns across four thickness bands. Columns 3 and 4 both cover H≤8 processes but apply to different steel grade groups with different preheat requirements.
| Thickness | Col 2: H≤16 | Col 3: H≤8 (Groups A, B) | Col 4: H≤8 (Group C) | Col 5: H≤4 |
|---|---|---|---|---|
| Up to 20 mm (3/4 in) | None* | None* | 10°C (50°F) | 10°C (50°F) |
| Over 20 to 40 mm (3/4 to 1-1/2 in) | 65°C (150°F) | 10°C (50°F) | 65°C (150°F) | 50°C (125°F) |
| Over 40 to 60 mm (1-1/2 to 2-1/2 in) | 110°C (225°F) | 65°C (150°F) | 110°C (225°F) | 80°C (175°F) |
| Over 60 mm (2-1/2+ in) | 150°C (300°F) | 110°C (225°F) | 150°C (300°F) | 110°C (225°F) |
* None: No minimum preheat required for thicknesses up to 8 mm (5/16 in) only. When base metal temperature is below 0°C (32°F), preheat to at least 10°C (50°F) and maintain during welding.
Cold weather welding: Welding shall not be done when the ambient temperature is below -18°C (0°F) except with the engineer's consent per Table 5.3 Note 1. When the base metal temperature is below 0°C (32°F), preheat to at least 10°C (50°F) regardless of the table value.
Preheat zone: The preheat zone shall extend at least the thickness of the part being welded, with a minimum of 75 mm (3 in), both laterally and in advance of the welding per Table 5.3 Note 2.
Quenched and tempered steels: For Q&T steels (700Q, A514, A517), maximum interpass temperature is 200°C (400°F) for thicknesses up to 40 mm and 230°C (450°F) for greater thicknesses. Heat input shall not exceed the steel producer's recommendations.
SAW waiver: Table 5.4 provides a preheat waiver for single-pass SAW fillet welds based on carbon equivalent, but this does not apply to quenched and tempered steels.
W59 vs D1.1: CSA W59 uses four process/hydrogen columns while D1.1 uses seven process categories (A through G). The steel grade groupings also differ. A WPS qualified under one standard cannot be used under the other without verification that all applicable requirements are met.
The most significant structural difference between CSA W59 Table 5.3 and AWS D1.1 Table 5.11 is how each standard classifies welding processes. D1.1 uses seven categories (A through G) that differentiate by both process type and hydrogen level, while W59 uses four columns that group processes primarily by hydrogen designator level. In W59, GMAW and GTAW are treated identically to SMAW/FCAW/SAW with H≤8, because gas-shielded processes inherently produce low diffusible hydrogen.
Another key difference: W59 Columns 3 and 4 both cover H≤8 processes but apply to different steel grade groups. Column 3 covers lower-strength steels (Groups A and B, up to 380W or A572 Gr 55), while Column 4 covers higher-strength steels (Group C, 400A through 550AT or A572 Gr 60-65). This distinction recognizes that higher-strength steels have greater susceptibility to hydrogen cracking and therefore require higher preheat temperatures at the same hydrogen level.
CSA W59 uses Table 5.3 to determine minimum preheat and interpass temperatures. The lookup requires three inputs: the steel grade group (which maps to one of four columns based on composition and strength), the welding process and hydrogen designator (H≤16, H≤8, or H≤4), and the material thickness. The table has four thickness bands: up to 20 mm, over 20 to 40 mm, over 40 to 60 mm, and over 60 mm. Higher-strength steels and thicker sections require higher preheat temperatures.
CSA W59 Table 5.3 uses three hydrogen designator levels: H≤16 (non-low-hydrogen or no hydrogen designator), H≤8 (low-hydrogen electrodes or GMAW/GTAW processes), and H≤4 (very-low-hydrogen, required for quenched and tempered steels like 700Q and A514). The designator indicates the maximum diffusible hydrogen content in millilitres per 100 grams of deposited weld metal. Lower hydrogen levels allow lower preheat temperatures for the same steel group and thickness.
CSA W59 Table 5.3 and AWS D1.1 Table 5.11 serve the same purpose but organize data differently. W59 uses four process/hydrogen columns (Columns 2 through 5) grouped by hydrogen designator, while D1.1 uses seven process-based categories (A through G). W59 uses metric units (Celsius and millimetres) as primary, while D1.1 uses imperial. W59 references CSA G40.21 steel grades like 300W and 350W alongside ASTM grades. The underlying preheat philosophy is the same: slow the cooling rate to allow hydrogen diffusion and prevent cold cracking.
When Table 5.3 shows None with the dagger footnote, no minimum preheat is required for that combination, but only for thicknesses up to 8 mm (5/16 in). For thicknesses over 8 mm but still within the up to 20 mm band, preheat is required. Additionally, when the base metal temperature is below 0°C (32°F), you must preheat to at least 10°C (50°F) and maintain that temperature during welding, regardless of what the table shows.
For quenched and tempered steels (CSA G40.21 700Q/700QT, ASTM A514, A517), CSA W59 Table 5.3 Note 2 sets maximum interpass temperatures of 200°C (400°F) for thicknesses up to 40 mm and 230°C (450°F) for thicknesses greater than 40 mm. Heat input shall not exceed the steel producer’s recommendations. These limits protect the quenched and tempered microstructure from being softened by excessive heat during welding.