Final answer:
Joining copper water pipes is typically done through a soldering process using a propane torch and solder. However, when replacing lead pipes connected to iron plumbing with copper, special considerations are needed to prevent galvanic corrosion, such as using dielectric unions to isolate the metals.
Step-by-step explanation:
When joining copper water pipes, the technique commonly used is called soldering, which involves heating the pipe joints with a propane torch and applying a solder material that melts and seals the connection. The process typically begins with thoroughly cleaning the ends of the pipes and the fittings to ensure a clean surface for the solder to adhere to.
A flux is then applied to the cleaned surfaces, which helps the solder flow smoothly and prevents oxidation during heating. The pieces are assembled, and heat is applied to the joint with a propane torch. When the joint is hot enough, solder is touched to the joint and melts, flowing into the gap between the pipe and fitting, creating a watertight seal upon cooling.
Regarding the scenario of replacing lead water pipes with copper when the rest of the plumbing is iron, it's important to consider the potential for galvanic corrosion when different metals are in contact. Galvanic corrosion occurs when two dissimilar metals are connected in the presence of an electrolyte, such as water. Iron and copper can form a galvanic couple, leading to rapid corrosion at the joints and potential leaks. To prevent this, a plumber would use dielectric unions or other methods to electrically isolate the metals and reduce corrosion risk.