What is the purpose of shielding gas in welding?

• A. To cool the weld faster.
• B. To protect the molten weld pool from atmospheric contamination (oxygen, nitrogen, hydrogen), preventing oxidation and porosity.
• C. To clean the base metal before welding.
• D. To increase the arc temperature.

Answer: (B)

Shielding gas provides a protective blanket around the molten weld pool to keep it from contact with the atmosphere. By keeping oxygen, nitrogen, hydrogen, and other atmospheric elements away, it prevents oxidation, porosity, and other defects that would weaken the weld. The gas type is chosen to suit the process and material, but the primary purpose remains shielding the molten metal from air. The other ideas—cooling the weld, cleaning the base metal, or increasing the arc temperature—aren’t the main role of the gas: cooling comes from heat flow and material properties, cleaning is done by prep work or flux/slag, and arc temperature is controlled by the welding current and voltage, not the shielding gas.