What is the primary purpose of preheat and interpass temperature control in field welding?

• A. To control cooling rate and reduce cracking risk.
• B. To increase the speed of welding.
• C. To improve aesthetics of the weld.
• D. To extend the welding time indefinitely.

Answer: (A)

The main idea is to control how quickly the welded metals cool so cracking is less likely. Preheating and keeping the interpass temperature higher between passes slow down the cooling rate of the weld and surrounding metal. Slow cooling helps prevent the formation of brittle, hard microstructures in the heat-affected zone and gives hydrogen time to diffuse out instead of turning into cracks. This is especially important on thicker sections or certain structural steels where hydrogen-induced or delayed cracking can occur. By controlling the heat input in this way, you improve weld integrity and reduce the risk of cracking, rather than trying to weld faster, improve appearance, or stretch the process time indefinitely.