What shielding gases are most commonly used for FCAW?

• A. Helium
• B. Oxygen
• C. Nitrogen
• D. Carbon dioxide (CO2) or argon/CO2 blends

Answer: (D)

In FCAW, shielding gas protects the weld pool from the surrounding air to prevent oxidation and contamination. When gas-shielded FCAW is used, the most common choices are carbon dioxide alone or mixtures of argon with carbon dioxide. CO2 is inexpensive and provides reliable arc stability and penetration for carbon steels, while adding argon to CO2 can improve arc stability and reduce spatter, giving cleaner welds on a wider range of steels. Helium is costly and less common for FCAW, and oxygen or nitrogen as shielding gases can cause oxidation, porosity, or other weld defects, so they’re not typical choices.