Before brazing, what is the purpose of circulating nitrogen through copper tubing?

Circulating nitrogen through copper tubing before brazing primarily serves to prevent oxidation. When copper is heated during the brazing process, it can react with the oxygen in the air, leading to the formation of copper oxides. These oxides can hinder the integrity of the joint and result in a weak bond. By introducing nitrogen, which is an inert gas, it displaces oxygen and creates a protective environment that minimizes oxidation. This ensures that the brazed joint remains clean and strong.

The other purposes mentioned, such as cooling the tubing, cleaning the tubing, or replacing refrigerant, either do not apply to the brazing process or are not the primary reasons for using nitrogen in this context. The main focus is on preserving the quality of the joint by preventing harmful reactions during the heating process.