How to get continuous curtain rod across 18 ft room without support?

Even if you use galvanized pipe, I would think you'll need supports.

Why would you need it to be without support? I can't think of anything you could do that would work for that long of a span. Would it be possible to support from the ceiling?

18' is too long a run without support. Must have wall or ceiling supports for it to be feasible.

I think you could do a wire anchored at each end. If that’s your style - very modern. If you want a solid rod I think you’re stuck with at least one support in the middle.

Where is it going? Across ceiling or wall. One that long won't support much weight on it at all without adding supports or using something like pipes, and even that may start warming from weight in the middle and loosening the end supports or pulling them out. Perhaps you could go with two curtains and put support in the middle where they will come together.

Over an 18' span, hanging draperies will most likely necessitate 3 supports, in addition to end mounts. Why not mount two 9' rods, each with center support?

Maybe one of those channeled track systems hospitals suspend their privacy curtains along. The channel hardware would be mounted to the ceiling and hidden with a built in cornice board or wood beam depending on your design style.