With a machine shop for a business you end up with a lot of surplus material that can't be used. Most times it gets scrapped and recycled, but some pieces end up sitting around the lot. There can be lot of different uses for these items with the right creative perspective. I found such a way on the streets of Austin.
I am fond of the industrial look because of it's rustic and flaw filled nature, and turning these steel tubes into planters* is a great repurpose. They're sturdy and they will last a long time, unlike other materials that will break down. Adding a few of these in my landscape would give it less of an antiseptic tone. This is being added to my project list.
*note | Heat tolerant plants and a shady spot are things to consider if using steel containers. They will heat up very quickly and can burn the roots.