During the brazing process, which gas should be purged through the copper tubing to prevent oxidation or scale formation?

• A. Argon
• B. Helium
• C. Nitrogen
• D. Oxygen

Answer: (C)

Purging the copper tubing with an inert gas during brazing keeps the interior free of air and moisture, so copper doesn’t oxidize at the high temperatures involved. Oxidation forms copper oxide and oxide scale, which can prevent proper wetting by the braze filler and clog the path, weakening the joint. Nitrogen is chosen because it is inert, readily available, and inexpensive, making it effective at displacing oxygen without reacting with copper or flux. While argon or helium are also inert, they are typically more costly for routine purging, so nitrogen is the common choice. Exposing the copper to oxygen would promote oxidation, not prevent it, so oxygen is not suitable.