Backing plates are used in welding for which purpose?

Backing plates in welding serve an essential role in aligning pipes and ensuring that the weld metal does not protrude into the interior of the pipe. This alignment is crucial for maintaining the integrity and precision of the weld joint, which is significant in applications where the pipes carry fluids or gases. A properly aligned joint helps prevent leaks and ensures that the structural integrity of the piping system is maintained.

Furthermore, backing plates provide a surface against which the weld can form, allowing for better control of the weld pool and facilitating a more uniform welding process. This not only improves the overall quality of the weld but also helps in producing a stronger joint. The fact that they prevent weld metal from protruding inside the pipe is particularly important, as protrusions may disrupt the flow of materials through the pipe and can create points for potential future corrosion or other failures.

The other options, while relevant to various aspects of welding and metal work, do not capture the primary purpose of backing plates effectively.