A maintenance welder is tasked with repairing a heavily corroded structural member using FCAW-S. The joint preparation involves grinding to remove surface rust and scale. During welding, they notice excessive smoke, arc instability, and a very porous weld bead. Which of the following is the most likely contributing factor to these issues?

Question: A maintenance welder is tasked with repairing a heavily corroded structural member using FCAW-S. The joint preparation involves grinding to remove surface rust and scale. During welding, they notice excessive smoke, arc instability, and a very porous weld bead. Which of the following is the most likely contributing factor to these issues?

Answer options:

• The use of DC Electrode Positive (DCEP) polarity ✅ Insufficient cleaning of the base metal, leaving embedded contaminants
• The wire stick-out is too long for the process
• An excessively high welding voltage setting

Correct answer: Insufficient cleaning of the base metal, leaving embedded contaminants

Explanation: Even with FCAW-S, which is more tolerant of mill scale and rust than GMAW, embedded contaminants from heavy corrosion, especially in areas not thoroughly ground out, will cause severe porosity, excessive smoke, and arc instability. DCEP is the correct polarity for FCAW, and while excessive voltage or stick-out can cause issues, incomplete cleaning of heavily corroded material is a primary cause of major porosity.