Interpass and preheat temperatures shall be used in which conditions?

• A. For all welds
• B. For highly strained welds
• C. Never
• D. Only for aluminum

Answer: (B)

Controlling how hot the metal is before and between passes helps manage how the weld cools and how hydrogen behaves in the metal. In welds that are highly restrained or highly stressed, the risk of cracking rises because the material can’t easily relieve the stresses as it solidifies. Preheating the base metal slows the cooling rate and reduces the hardness of the heat-affected zone, while keeping the interpass temperature within a controlled range between passes prevents rapid temperature changes that could trap stresses or promote cracking. Because of this, interpass and preheat temperatures are used specifically to manage cracking risk in highly strained welds, improving ductility and soundness. They aren’t required for every weld, aren’t exclusive to aluminum, and aren’t something to ignore in high-stress situations.