Back purging in stainless steel welding is used to prevent oxidation and chromium oxide formation at the weld root.

• A. To prevent oxidation and chromium oxide formation at weld root
• B. To improve color
• C. To increase deposition rate
• D. To reduce cooling time

Answer: (A)

Back purging protects the weld root from exposure to air so the root doesn’t oxidize during welding. Stainless steel relies on a chromium oxide layer for corrosion resistance, and allowing oxygen to reach the root can form oxides that contaminate or deplete this protective film. Using an inert gas on the backside keeps the root in an oxygen-free environment, producing a cleaner, more corrosion-resistant root and reducing the chance of oxide-related defects. The other options don’t address protecting the root from oxidation or preserving the stainless steel’s corrosion resistance, which is the main purpose of back purging.