With respect to welding inspection, why is the mix of shielding gases discouraged?

The mix of shielding gases is discouraged primarily because it can lead to inconsistencies in weld quality. Each shielding gas has specific properties that influence the behavior of the arc, the penetration of the weld, and the overall characteristics of the weld bead. When different gases are mixed, it can create variability in these properties, which can result in weld defects such as porosity, improper fusion, or insufficient penetration.

Inconsistent weld quality can affect the integrity and strength of the welded joint, which is especially critical in pipeline welding where structural robustness is a priority. Therefore, maintaining a consistent type of shielding gas ensures that the welder can rely on predictable behavior during the welding process and achieve the desired quality of the weld.