A welder is working on a project requiring compliance with CSA W59 for welded steel construction. The project involves a structurally significant moment connection in a building frame. What is the MINIMUM preheat temperature generally required for welding 25 mm thick CSA G40.21 350W steel using an approved low-hydrogen electrode in an ambient temperature of 10°C, according to CSA W59?

Question: A welder is working on a project requiring compliance with CSA W59 for welded steel construction. The project involves a structurally significant moment connection in a building frame. What is the MINIMUM preheat temperature generally required for welding 25 mm thick CSA G40.21 350W steel using an approved low-hydrogen electrode in an ambient temperature of 10°C, according to CSA W59?

Answer options:

• 0°C
• 20°C ✅ 50°C
• 70°C

Correct answer: 50°C

Explanation: According to CSA W59, for 25 mm thick CSA G40.21 350W steel, a minimum preheat temperature of 50°C is typically required, even with low-hydrogen electrodes. This preheat helps to prevent hydrogen-induced cracking by slowing the cooling rate and allowing hydrogen to diffuse out of the weldment.