Which of the following statements about GTAW shielding gas selection is supported by the material?

• A. Mixing two or more gases is permissible
• B. Only pure gases can be used
• C. Oxygen is commonly used as shielding gas
• D. Hydrogen is never used in GTAW shielding

Answer: (A)

GTAW shielding gas selection often involves mixing two or more gases to tailor arc stability, heat input, and weld pool protection for different metals and thicknesses. Argon is a common base gas, and adding others like helium can increase heat input or adjust penetration; small amounts of hydrogen can be used for specific alloys to influence cleaning and wetting. So mixing gases is a deliberate and permissible practice to achieve the desired welding conditions. The other statements aren’t accurate because pure gases aren’t required in all cases, oxygen isn’t routinely used as the shielding gas in GTAW, and hydrogen is used in some applications rather than being never used.