What is the first pass of a multi-pass weld called?

The first pass of a multi-pass weld is referred to as the root pass. This pass establishes the foundational connection between the base materials and is critical for the overall integrity of the weld joint. The root pass is designed to penetrate deeply into the joint's base material, creating a strong initial bond and ensuring that the subsequent passes can be effectively layered on top. It is important because it sets the stage for the weld's geometry and strength, influencing the overall quality of the completed weld.

In contrast, the other terms in the options do not specifically apply to the first pass in the context of multi-pass welding. While "primary pass" might imply that it is a significant pass, it does not correctly denote the technical term used in welding practices. "Starting pass" also suggests a beginning phase but lacks the specific emphasis on the critical role that the root pass serves. "Integral pass," similarly, does not carry the definition pertaining to the initial layer and is less recognized in welding terminology related to multi-pass techniques.