Which statement about purging copper tubing during brazing is correct?

• A. Oxygen purging is safe
• B. Argon purging is required
• C. Nitrogen purging is best
• D. Oxygen purging could cause an explosion

Answer: (D)

During brazing, purging the copper tubing is done to displace air and any moisture and to protect the metal surfaces from oxidation while you heat the joint. Oxygen around the hot metal can greatly increase the risk of ignition if any flammable vapors or oils are present in the system. Those vapors can ignite or even explode when exposed to heat and an oxidizer, so introducing oxygen into the purge creates a dangerous situation. That’s why using oxygen to purge is avoided in favor of inert gases like argon or nitrogen, which displace air without providing an oxidizer.