If they are stainless, why not try using a fine abrasive paper on a small section and see what happens. I recently had some s/s manifold pipes to clean up, and tried this, which worked fine, but I wanted a highly polished finish, as they are on show, so took them to a local exhaust fabricator who polished them on his wheel, they looked a treat too, but a couple of thousand miles down the road, they are right back to where they were before. I've come to the conclusion that you either just leave them or wrap them.
