On chrome when it`s cooled off I use carburetor cleaner sprayed onto a terricloth rag. `Takes a little elbow grease, but it works every time without a scratch.
Guys seriously. This is simple. Buy some brass wool. It doesn't scratch at all. It's available at any marine supply and at least here in Florida it's available at most motorcycle parts shop.
Brass Wool and a little water will remove the nastiest scuffs or residue from your pipes and yes it's save for black pipes.