Funny you should say this ... my rainwater supply pipes on the outside of the house kept freezing.
When water freezes it forms giant molecules which take up about 10% more volume than the water from which they formed. The forces involved are enormous and you will only be aware of cracked pipes when the water thaws.
Here are some ideas .... push joints at regular intervals
which can easily be rejoined after the thaw.
Or an internal air pipe notted at each end which will be compressed when freezing occurs - this pipe to fill as much of the internal pipe diameter as possible.
Or blowing air into the pipe via a valve when freezing likely to displace the water.
Or use of water solenoids which cut the water off and another which opens to drain the supply pipe.
Or increasing the diameter of the pipe will mean it will take longer to freeze - the heat content will vary as the square of the radius while the heat lost will vary as the radius of the pipe.
Nyge
April 2011