Final answer:
Copper fittings are cleaned before soldering or brazing to ensure proper adhesion, prevent contamination, and avoid problematic corrosion that can arise from contact with other metals, such as iron.
Step-by-step explanation:
Copper fittings are cleaned before soldering or brazing because the presence of any oxide, dirt, or grease can prevent the solder or braze from adhering properly to the copper surface. Clean surfaces ensure a good metallic bond between the fitting and the pipe, which is crucial for creating a strong and leak-free joint. Cleaning also removes any corrosion that may have formed on the copper, which can inhibit the flow of electricity during the soldering process, affecting the quality of the joint.
When metals like copper and iron are in contact, especially in the presence of electrolytes like water, corrosion can occur due to electrochemical reactions. Copper is less reactive than iron; thus, when they are connected, iron tends to corrode as it acts as an anode while copper acts as a cathode. This is why it's essential to avoid copper/iron direct contact in plumbing unless appropriate precautions are taken, like using dielectric unions.