Which of the following connections is suitable for joining 1.5-inch pipe?

The correct response indicates that any connection type can be suitable for joining 1.5-inch pipe. This is rooted in the understanding of the various methods available for joining pipes, with each method having its specific applications and advantages.

Threaded connections are commonly used for smaller pipes and can provide a reliable seal, making them a practical choice for 1.5-inch pipe installations, especially in systems where frequent disassembly may be necessary.

Welded connections offer a permanent and strong join, ideal for high-pressure applications or environments where leaks cannot be tolerated. Welds create a complete seal, which is advantageous for maintaining structural integrity.

Flanged connections are effective for larger and modular piping systems, allowing for easy assembly and disassembly. Flanges are particularly useful when maintenance access is required, or when joining different types of systems.

Since all these joining methods can be applied to 1.5-inch pipe, the selection largely depends on the specific application, pressure requirements, and the need for maintenance or flexibility in the piping system. Thus, it's accurate to say that any of these connection types can be suitable for a 1.5-inch pipe installation.