Well, you have to put them up for winter if it freezes. You might try putting one in ground and filling with cement for a piller and let it go thru a winter. If it cracks, you just paint the cracks and make it look intentional. Or if it cracks and falls off you will have a concrete piller. But you might also spray inside with release and put in some concret and then take off the pipe. When it dries put it back on for the summer. You could coat with a plaster or paint for decoration.

You can also use a few pieces of rebar stuck in the ground to stabalize them. But if it snows and freezes I think you'll have to take them in over winter. Or then you can wrap them in something, like an old bed sheet, then cover them with plastic to protect them.

I have a few of those pipes but haven't mosaiced them yet. I get frost here but no deep freezes and no snow. Use thinset should you mosaic them. It's cheaper than GEII.

There is a GJer on here named Robert and he makes funky birdfeeders out of pipe, etc. You should try doing a search. I've also seen the drain pipe used in gardens by "planting them in the garden in varying heights and filling them with dirt and planting directly into them and letting the plants trail over the edge. I've seen them grouped together and as single focal points.