I am moving my gas dryer about 8 feet down a wall. I can I put an elbow on the stub coming out of the wall and then run a length of black pipe along the wall to the new location? Or does the pipe have to be inside the wall?
If it can be run along the outside of the wall, what is the best way to secure it to the wall?
It will all be hidden behind appliances so it will not be an eyesore -- just want to avoid ripping out the drywall at this point.
Should be fine so long as the pipe is indeed covered/blocked by appliances, cabinets, etc in front of it. As for securing it, there are various ways to do it, but the easiest and cheapest would be little pipe straps that are made for 1/2" hard pipe.
If your pipe isn't flat against the wall though, those straps won't work. You'll need to put some kind of wood blocks back there, attach those blocks to the studs, and then attach the pipe straps onto the blocks.