Excessive penetration on a root pass is likely caused by which factor?

Excessive penetration on a root pass in welding is typically caused by travel speeds being too low. When the travel speed is reduced, the heat input increases at the weld pool, allowing it to penetrate deeper into the base material. The heat has more time to affect the material, which can lead to a deeper and often wider penetration than desired.

Adequate control of travel speed is essential to achieve the right balance of penetration for the joint design. A speed that is too low can not only lead to excessive penetration but can also create issues such as burn-through or warping of the base metals.

The other factors, while they can cause various issues in welding, do not directly contribute to excessive penetration in the same manner. For instance, a high travel speed might lead to insufficient penetration instead of excessive, and using an improper electrode angle or the wrong wire diameter primarily affects the deposition rate and the quality of the weld bead rather than directly influencing the depth of penetration.