Hot water pipes burst first?

Zman

I know there was a conversation a while back that touched on this but a recent experience got me thinking again...

I have 2 identical copper domestic water pipes (hot and cold) that are strapped to the wall of my garage with van hangers. Both pipes have a spring check at the bottom, about 3' of pipe and then a closed ball valve before they go to my pressure washer.

Last night, the garage door was left open with an outdoor temp of 3 degrees. Needless to say, the pipes froze. The hot water pipe split wide open and the cold was not even deformed. Keep in mind, neither pipe had been used in weeks, so the water in the pipe would have been the same temp at the beginning of the event.

I have always noticed that hot water pipes sustain more damage in freezeups than cold, but I have never had such a perfectly controlled (accidental) example.

So here is the theory. The cold water picks up dissolved gasses in treatment and transportation. When the water is heated at the house, some of the dissolved gasses come out of solution. The difference in gas content changes the amount the water expands? The gasses act as a cushion?

Thoughts?

luketheplumber

I think that I heard about hot water cooling faster that cold water before. I'll look this phenomenon up.

Larry Weingarten

Hi @Zman , lots to consider. I know dissolved gasses are supposed to come out of solution, but if it's essentially a closed system, where will those gasses go? Also, dissolved gas is no longer in a compressible form, is it? It isn't little bubbles that can be compressed. So, I'm wondering if it's something more mechanical, like a spring check that leaks just enough to prevent pressure from building in the freezing line. Of course ice could burst the pipe by itself... Maybe replace the lines with insulated PEX?? I'll be curious to see what others come up with. Sounds like a research project!

Yours, Larry

Zman

luketheplumber said:

I think that I heard about hot water cooling faster that cold water before. I'll look this phenomenon up.

That's the direction I was headed until I saw this. The temp of the water in both pipes was the same because they had not been used recently. The spring checks at the bottom should have negated thermal siphon. The only difference I can see is that hot water was previously heated. Both pipes where originally the same stick.

@Larry Weingarten
I thought that might be the thin spot in my theory. It could also be chance or a valve that leaks a little....

jumper

Here's a theory. Hot water pipes experience wider temperature swings. The copper either gets a bit weaker or more brittle? Next experiment is to freeze both hard copper and soft copper.

mattmia2

My guess would be that it simply was closer to the cold. The dissolved gas when it comes out of solution may collect somewhere and not be distributed to that branch and some dissolved mineral may be removed when you heat it, but the difference in freezing point wouldn't be significant because there is so little dissolved minerals relatively speaking.

luketheplumber

It's called the Mpemba Effect. You may be right about the gasses @Zman

Zman

jumper said:

Here's a theory. Hot water pipes experience wider temperature swings. The copper either gets a bit weaker or more brittle? Next experiment is to freeze both hard copper and soft copper.

I like where you are headed with this but...
I installed the pipes about 8 months ago. I have only put a few hundred gallons of 130 degree water through them.

mattmia2

And copper pipe is hard drawn. It is annealed where you solder it, but it is more or less already hardened.

psb75

When water gets heated oxygen and other gasses leave and come out of solution. The water then becomes more dense i.e. becoming closer to its solid state... that being ICE. So if you have two pipes sitting in a garage, one with cold water (never having been heated and full of gasses), and the other with water that was heated (with gasses having been driven off)....when chilled, which do you think will freeze FIRST--and BURST? Another unfortunate fact in plumbing: frozen water is BIGGER than liquid water.
Now...you might also ask yourself this perplexing question: how come ICE--which is water in its SOLID state, FLOATS on top of water- which is in its liquid state? Shouldn't a SOLID be residing at the bottom of the liquid?
There would be no life on earth if this were the case!

nicholas bonham-carter

Original discussion:

https://forum.heatinghelp.com/discussion/180471/which-freezes-first#latest

I believe that ice will become less dense than water, as it expands at the freezing temperature point, and so floats.
I like the gas bubble theory where the bubbles will act as miniature expansion tanks. It’s not so much a question of which freezes first, but rather which expands more as it freezes.—NBC

Zman

psb75 said:

Now...you might also ask yourself this perplexing question: how come ICE--which is water in its SOLID state, FLOATS on top of water- which is in its liquid state? Shouldn't a SOLID be residing at the bottom of the liquid?
There would be no life on earth if this were the case!

The when the water freezes it expands, it does not gain any measurable weight in the process. The ice is less dense than the water and therefore it floats.

Also, wood floats and ducks float, so if it weighs more than a duck, it must be a witch.
Sorry, I can talk about buoyancy without a little Monty Python...