The first pass of a multi-pass weld is known as the:

The first pass of a multi-pass weld is referred to as the root pass. This initial pass is crucial because it forms the foundation of the weld joint and establishes the penetration into the base material. The root pass ensures that the components being welded are fused together at their root, which is typically the area where the two pieces meet. Properly executing the root pass is critical for the overall integrity and strength of the weld, as it influences the quality of subsequent passes.

In multi-pass welding, each subsequent layer builds upon the root pass, contributing to the overall thickness and strength of the joint. If the root pass is not executed correctly, it may lead to flaws such as porosity, lack of fusion, or inadequate penetration, which can compromise the weld's performance under service conditions. Therefore, understanding the significance of the root pass is essential for anyone engaged in welding practices, particularly in refrigeration and similar applications where joint integrity is paramount.