When the base metal temperature is below 32°F, what is the minimum preheat temperature that must be applied before welding?

When the base metal temperature is below 32°F, what is the minimum preheat temperature that must be applied before welding?

• A. 50 °F
• B. 70 °F
• C. 90 °F
• D. 120 °F

Answer: (B)

When base metal is very cold, preheating is used to slow the cooling of the weld and the heat-affected zone, reducing the risk of hydrogen-induced cracking and excessive hardness. If the metal is below freezing, applying a minimum preheat helps keep moisture from freezing on the surface and gives hydrogen less time to diffuse into the weld. The minimum preheat temperature in this cold condition is 70 °F. That level is just enough to effectively slow cooling and reduce cracking risk without overdoing the heat, which could cause distortion or other metallurgical issues. A lower value like 50 °F wouldn’t provide sufficient protection in freezing conditions, while higher values (90 °F, 120 °F) exceed the minimum and aren’t required in this scenario.

When base metal is very cold, preheating is used to slow the cooling of the weld and the heat-affected zone, reducing the risk of hydrogen-induced cracking and excessive hardness. If the metal is below freezing, applying a minimum preheat helps keep moisture from freezing on the surface and gives hydrogen less time to diffuse into the weld.

The minimum preheat temperature in this cold condition is 70 °F. That level is just enough to effectively slow cooling and reduce cracking risk without overdoing the heat, which could cause distortion or other metallurgical issues. A lower value like 50 °F wouldn’t provide sufficient protection in freezing conditions, while higher values (90 °F, 120 °F) exceed the minimum and aren’t required in this scenario.