I would think it is more likely that there was a nick in the insulation from installation. If you're thinking that water would creep down between the copper and insulation, I would think that surface tension of the water would keep it from running, unless I'm not understanding surface tension correctly.
Another thing, I don't know if the expansion ratio of water to ice would be enough to split the insulation from the inside out. If water could get all the way down the insulation it would only be a small amount. Although the plastic would probably more brittle at these lower temperatures, I wouldn't expect it to split like a copper water pipe.
[This message has been edited by Jps1006 (edited 12-17-2005).]
