Kay wrote:
:::::
::: Hmmm...now I think I see where everyone's going wrong!...the pipe
::: and tap will both be (all but) drained, having turned off it's
::: water supply and left the tap open...what little there is in
::: there *cannot* expand sufficiently to burst a pipe.
:::
:: But wasn't it you who said
:::
::: The pipe contains 15 mm of water, encased in a 1 mm copper
:::::: sheath, the tap contains 25mm of water encased in a 10mm brass
:::::: sheath, which is going to freeze first?
::
:: ?

Yes I did say that and in the case of the pipe being horizontal, there is a
possibility, even with the water turned off, that the pipe and tap could
still contain water, (not under any pressure) and with the tap fully open,
it still cannot burst a copper pipe if it froze - it takes the easiest
route.

Anyway - I have (accidentally) frozen cans of lager in the deep freeze many
times and they haven't bursted the can - the beer is already under pressure,
the material is about a tenth of the thickness of copper pipe and they have
been in there for days without bursting, I think people underestimate the
strength of water pipes...if the tap is open, the water/slush/ice will
escape through there before getting through the metalwork.