Interior copper tubing is usually joined by:

Interior copper tubing is typically joined by soldering because this method creates a strong, durable, and leak-proof joint. Soldering involves melting a filler metal (the solder) and allowing it to flow into the joint between two pieces of copper tubing. When the solder cools, it solidifies and bonds the two pieces together, making it essential for ensuring the integrity of plumbing and HVAC systems where copper tubing is commonly used.

This technique is particularly advantageous with copper because it offers excellent thermal and electrical conductivity, which is crucial in applications requiring efficient heat transfer. Moreover, soldering is a well-established method in the plumbing industry and is often utilized to connect pipes in water supply systems, heating systems, and refrigeration.

The other methods such as welding, threaded fittings, and compression fittings are less common for interior copper tubing due to various limitations such as complexity, the need for specialized equipment, or less reliable leak prevention. Soldering stands out as the preferred method for its combination of reliability, ease of use, and effectiveness in forming secure connections.