Originally Posted by oldtool2
I find that hard to believe.
I have never heard of any piping system that would / could not break. Water expands when it freezes. It is one of the few liquids that does and that pressure has got to go somewhere. Even soft copper will split.
Small metal pipe is manufactured using two techniques. Almost all pipe is rolled from flat stock and welded where the ends come together. The weld is a weak spot that usually splits when freezing water expands inside it. (Actually, water contracts as it cools until it reaches 4C when it starts expanding.) Seamless pipe is made by passing a rod through rollers that squeeze it in different directions which opens up a hole in the middle of the pipe. Seamless pipe is much stronger than seam welded pipe and also is much more expensive.
PEX pipe is a plastic which is a lot more flexible than metal. Plastics do not have metal's rigid structure and can have the ability to stretch a little then return to their original size. The following quote is from Black Diamond Plumbing Supply's (Chicago) web site: "Due to its flexibility, PEX has a small margin of expansion under the damaging pressure caused by ice formation. If the weather gets cold enough, PEX pipes can and will freeze like any plumbing. However, PEX may be less likely to rupture as a result of freezing."
The effects of freezing water are obvious to anyone who drives in the northern parts of the US. Potholes arise from water getting into a crack in pavement, freezing and expanding with its resulting damage to the road material. Water freezing in a rock with a crack in it can split the rock, part of erosion of mountains.