When is it permissible to remove the lineup clamp before the root bead is completed for butt welds?

The correct choice highlights the importance of maintaining joint integrity during the welding process. It is permissible to remove the lineup clamp before completing the root bead for butt welds when the completed part of the bead itself is in equal segments spaced around the joint. This requirement ensures that the joint remains properly aligned and supported, preventing any distortion or misalignment that could occur if the clamp is removed prematurely.

This practice allows the welder to assess the quality of the root pass and make adjustments as necessary before proceeding with subsequent welding passes. By ensuring that the bead is distributed evenly around the joint, this approach minimizes the risk of uneven thermal contraction during cooling, which can lead to defects such as cracking or warping.

In contrast, the other choices suggest practices that could compromise the integrity of the weld joint. For example, removing and rewelding the completed part after removing the clamp might lead to alignment issues or added stress on the joint. Peening the completed part before clamp removal creates additional concerns regarding the weld's cooling and stress distribution, which are not aligned with best practices for maintaining joint stability. Therefore, the chosen answer reflects the best practice for ensuring the quality and integrity of butt welds in pipeline welded joints.