Below what temperature would require engineer consent to weld?

• A. -40C (-40F)
• B. -18C (0F)
• C. -10C
• D. 0C

Answer: (B)

Welding at very low temperatures changes how the metal behaves—steel becomes more brittle and its toughness drops, which raises the risk of cracks or brittle failure in the weld and heat-affected zone. Because of this, codes require additional oversight when welding in cold conditions to ensure the joint will perform in service.

The boundary temperature where this extra approval kicks in is -18°C (0°F). Below this temperature, engineer consent is required to weld, to account for the cold impact on toughness and to determine any needed special measures (such as preheating, adjusted heat input, or other safeguards). Temperatures at -18°C or warmer do not trigger that required consent.

So, -18°C is the threshold value that defines when engineer consent is needed.