workbenches shouldn't move
I would use two french cleats, one along the top, the other along the bottom. Then to prevent it from lifting up, I'd screw a few screws into the studs which can be removed later if necessary.
Another approach is to use plywood panels for braces instead of the pipes which will be difficult to attach being round and all.... :frown2: If the design is meant not to have legs protruding into the shop or on the floor, that's cool, but you will want as many braces as possible, like every 36" or so. That's about the limit for a span of 3/4" material. If you double it, two layers, it will make a better bench top also.
One long bench can be held in place by the weight of the "stuff" you place on top. If you like a clean work space then you will need some screws to hold it down. If you mount a vise, you will especially want it very secure. A slip with a chisel may mean a serious injury.
I don't see the need for individual sections of shorter lengths myself, but you may have other reasons...?
The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)