In article , "Dave Plowman (News)"
wrote:

why call it a /compression/ joint then ? in your world it would be
called a deformation joint which it isn't, it's a /compression/ joint.
methinks you're splitting hairs, why is anyones guess but if the
copper *tube* /deforms/ the joint is and will be defective.

Not so. I've taken many apart, which after removing the olive, show
clear signs of the pipe being indented under where the olive was. And
non of them leaked. If you've not seen this I'd say you have little
experience.

The indentation of the pipe makes me to wonder if replacing old olives
when re-using compression joints might not always be a good thing. I'm
wondering what happens if the new olive doesn't line up exactly with the
groove created by the old one, this could lead to a much shorter area of
tight contact with the pipe and perhaps a less reliable seal. I've not
had much experience with plumbing so I'm not trying to put forward a
case for or against replacing olives, just looking for advice. The
compression joints I've made invariably leaked slightly to start with
but sealed OK after a bit more tightening. I'll be replacing quite a few
radiator valves with TRVs soon so I'd welcome any opinions on this from
the experts.

--
Mike Clarke