What is the purpose of back welds in welding?

The purpose of back welds is fundamentally to ensure that a weld joint is completed as indicated by the welding symbols on the fabrication drawings. These symbols provide critical information regarding the type, size, and extent of the weld necessary for the structural integrity of the assembly. By applying a back weld, the welder ensures that any incomplete or insufficient weld at the root of a joint—particularly in cases involving joints that could be susceptible to stress—meets the specifications outlined in the welding documentation. This not only fulfills design requirements but also helps prevent potential weaknesses in the weld area.

While enhancing the aesthetic appearance, providing support to the initial weld, or increasing the overall weld size may be secondary benefits or considerations in certain contexts, the main goal of a back weld is to comply with the defined welding requirements to ensure the weld is effectively completed according to the engineering specifications.