During a flux-cored arc welding (FCAW) repair on a heavy excavator boom, the technician notices excessive porosity in the weld bead. The gas shielding is confirmed to be flowing correctly. What is the most likely cause of this porosity?

Question: During a flux-cored arc welding (FCAW) repair on a heavy excavator boom, the technician notices excessive porosity in the weld bead. The gas shielding is confirmed to be flowing correctly. What is the most likely cause of this porosity?

Answer options:

• Too high wire feed speed. ✅ Contaminated base metal surface.
• Too low welding voltage.
• Travel speed is too slow.

Correct answer: Contaminated base metal surface.

Explanation: Contaminated base metal, such as rust, paint, oil, or moisture, is a very common cause of porosity in welds across various processes, including FCAW, because these contaminants vaporize and become trapped in the solidifying weld metal. While other factors can influence weld quality, contamination is a primary source of porosity. High wire feed speed or low voltage can lead to lack of fusion or inadequate penetration, and slow travel speed can cause excessive heat input or a large, convex bead, but are less direct causes of porosity.