Why is it necessary to use flux on a soldered joint?

Using flux on a soldered joint is necessary primarily because it serves to chemically clean the surfaces of the joint. When two metal pieces are being soldered, any oxide, grease, or other contaminants present can inhibit the adhesion of the solder. Flux helps to remove these impurities and prevents oxidation during the soldering process, ensuring that the metals bond effectively.

The cleaning action is crucial because a clean surface allows the solder to flow smoothly into the joint, promoting a strong and durable connection. Without using flux, the solder might not adhere properly, potentially leading to joint failure. This role of flux is essential in ensuring the integrity and reliability of the joint, especially in plumbing applications where leaks can have significant consequences.