Argon is also good for welding in deep grooves because it is denser than air.

• A. It is cheaper than air.
• B. It is denser than air, improving shielding in deep grooves.
• C. It reacts with the base metal to form nitrides.
• D. It conducts heat away too quickly.

Answer: (B)

Shielding gas effectiveness depends on how well the gas blankets the weld area. Argon is denser than air, so it stays around the molten pool longer and resists being blown away by convective currents from the arc and heat. In deep grooves, the geometry makes it easy for air to reach the weld and for shielding gas to escape, so a denser, more persistent blanket helps keep oxygen and nitrogen out of the molten metal, reducing oxidation and porosity. Argon’s inert nature means it won’t react with the base metal, which is also important for keeping the weld clean.

The other ideas don’t fit as well: shielding gas cost isn’t the deciding factor in deep grooves, argon isn’t reactive with the metal, and shielding gas isn’t used to conduct heat away—argon is a poor conductor of heat, and its job is protection, not cooling.