In pipeline welding, what does “preheating” help to prevent?

Preheating in pipeline welding is primarily employed to prevent weld cracking that can occur due to rapid cooling. When a weld is made on thicker materials or in colder environments, the temperature difference between the molten weld metal and the surrounding base material can lead to thermal stresses as the weld cools rapidly. These stresses may cause the weld to crack, particularly in materials that are more susceptible to brittle fracture.

By preheating the base metal before welding, it helps to reduce the cooling rate of the weld. This allows the molten metal to cool more gradually, which decreases the likelihood of high-stress zones forming in the heat-affected zone of the weld. Therefore, preheating aids in ensuring a more robust and ductile weld joint, thereby enhancing the integrity and performance of the welded pipeline.

Other options presented refer to different aspects of welding, but they do not directly relate to the purpose of preheating in preventing weld cracking from rapid cooling.