In welding, why are multi-pass welds sometimes necessary?

Multi-pass welds are often necessary to achieve the required joint strength and fill thicker sections. When welding materials that have a significant thickness, a single pass may not provide the depth of penetration needed to create a strong and durable weld. By layering multiple passes, welders can ensure that each layer properly fuses with the base materials and with previous layers, resulting in a weld that meets the structural integrity requirements.

This technique is especially important in applications where the welded joint will experience significant stresses or loads. Additionally, filling thicker sections with multi-pass welding ensures that the weld pool can effectively accommodate the variations in thickness, leading to better mechanical properties throughout the joint. As a result, multi-pass welds contribute to overall joint performance and longevity.

While the other options address different aspects of welding, they do not specifically capture the necessity of multi-pass welds as effectively as the need for adequate strength and the ability to handle thicker base materials.