David Billington wrote:

Why does the galv flake and is that inside or outside or both. I put
galv pipe handrails at my mothers place over ten years ago and the
external surface, while a bit weathered, is otherwise still perfect, ...

Likely a matter of degree, and perception. It wouldn't have to flake
much to cause problems in air tools, but that same flaking on the
outside would not be noticed.

Bob