What is the purpose of applying flux in copper pipe soldering?

• A. To improve solder flow and prevent oxidation
• B. To coat the pipe with a protective color
• C. To melt the pipe
• D. To clean the outside surface

Answer: (A)

Flux is used to prepare copper surfaces for soldering by keeping them clean and preventing oxidation as heat is applied. When copper gets hot, a thin oxide forms and solder won’t wet the surface well. Flux removes that oxide and stays on the joint to keep the surface active, which lets the molten solder flow into the joint and wet the metals properly. This results in a solid, leak-proof bond. It isn’t about coating the pipe with color, melting the pipe, or simply cleaning the outside surface—those aren’t the roles of flux.