Which type of joint is most commonly used in plumbing to connect two pipes?

The solder joint is the correct choice for connecting two pipes, particularly in plumbing systems that utilize copper piping. This type of joint works by melting solder, typically made from a tin-lead or lead-free alloy, to create a strong, watertight seal between the pipe and fitting. The heat from a torch or soldering iron is applied to the joint, which heats the metals sufficiently to allow the solder to flow into the gap.

Solder joints are favored in plumbing due to their reliability in preventing leaks, their ability to withstand the pressures of typical plumbing systems, and their resistance to corrosion when properly applied. Additionally, solder joints can be used in both above-ground and underground plumbing applications, making them versatile for a variety of installations.

In contrast, welded joints are generally used in industrial applications and require higher temperatures and equipment that may not be suitable for most home plumbing tasks. Threaded joints rely on the mechanical engagement of threads and are effective for certain pipe types, but are not as commonly used for fluid transportation due to potential leak points. Compression joints provide an easy installation method and are used in some applications, but they do not offer the same level of enduring strength as solder joints in high-pressure environments.