Ask A Scientist© Environmental Earth Science Archive

name         Dennis T.
status       other
age          50s

   Question -   At sea level, water begins to freeze at 32 degrees F. Is
there a point below 32 degrees F. that the ice reaches a maximum expansion?

I work for a public drinking water utility company.  The question came up
regarding damage to water pipes resulting from temps below 32
degrees.  Note: Although the temperature gets below the 32 degrees and
will freeze, it usually seems that our pipes begin to burst when the temp
gets down to around 20 degrees F.
-----------------
My guess is real life is different than experiments.  When my  furnace went
out , I think it was 20 outside air but inside it was 40.  the reason latent
heat, objects retain heat and gradually lose it.  So, it your case, the air
inside, the pipes, actually the diameter of the pipes is also in the mix.
Water in a free state freezes at 32 ( even then the factors are depth,
surface area etc).  So my point what conditions effect the water are your
key.
I do not know the molecular behavior , but it does not seem logical to me that
a maximum occurs before a stage change.
The solution to your pipes is wrapping with wire, the intermittent current
warming the pipes and keeping the temperature inside above freezing.

James Przewoznik
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No, ice does not expand as it gets colder.

When water freezes, it increases in volume about 9%.  The ice then shrinks
as the temperature decreases.  The shrinkage is tiny, about 0.4% going from
30F to -50F.

As a side note, liquid water is densest at a temperature of 39.2F.  The
density differences at higher and lower temperatures are very tiny.
Cooling 39.2F water to 0F  expands it only 0.01%.

Another note, there are at least 12 forms of ice. Most can be obtained only
in the laboratory under high pressure.

It is likely that the bursting at 20F is due to parts of the water system
that are not yet frozen at 32F finally freezing at the colder temperature.

Bob Erck
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It is possible to supercooled water, but it is not likely that this would
happen in the environment of a water pipe. There are too many sites for ice
crystals to form. The critical temperature of ~ 20F probably has to do with
how cold it must get in order to freeze enough water in the pipe that the
pipe plugs and having no where to go, the pressure build up is extreme.
There are many excellent web sites on the properties of water and ice if 
you do a Google search on the topics "properties of ice" or "properties of water".

Vince Calder
=====================================================
It usually seems that our pipes begin to burst when the temp
gets down to around 20 degrees F
---That is interesting.

No, water in the solid phase has normal expansion characteristics
(unlike the liquid phase: expanding with cold just before freezing).

Ice's temperature coefficient of expansion is about 50 ppm/degC
(, at the 
bottom).
This is a positive number, meaning that ice expands with heat and 
contracts with cold just like almost all other materials.
Great reference by the U.S. Coast-Guard 
at  .
Density of ice vs. temperature 
at  .

First, if your pipes are in the ground,
be sure you are measuring the temperature of the pipes, not of the air above.
Ground stores a significant amount of heat and is likely to be warmer than 
your latest cold-snap.
How much warmer depends on depth.

And any ongoing flow of water through the pipes will probably carry in 
higher temperatures 32F or higher.
Suppose ice builds up slowly on the pipe walls, in competition with the 
flow of slightly warmer water running through the center.
It is possible that no complete plug of ice forms anywhere along your pipe 
until significantly colder than 32F.
When the first complete plug forms (likely to be at some point above the 
ground),
then there is trapped water, gradually freezing and building up pressure 
in the pipe.
If you had a thermometer directly on or in the pipe and this happened,
the thermometer would never show less than 32F until the hours _after_ the 
pipes had burst.

At , look at the blue line.
You can see there that ice's density (the blue line)
is slightly decreasing with increasing temperature, so it seems that
stable ice does not expand as it gets colder.

But the green line at the same place may offer an explanation for your 
bursting:
Perhaps the water in the pipe is pure and still, so it supercools (fails 
to solidify) for about 6 degrees C.
This is not a difficult degree of supercooling to find.
Then at 20F it finally freezes, more rapidly than usual.
This would raise the pressure quickly and burst the pipes promptly.
If you had a thermometer directly on or in the pipe and this happened,
the temperature would gradually go down to 20F, all water,
then when freezing started it would jump up to 32F until freezing was 
complete,
and then slowly decline to 20F again, this time all ice.
Somewhere during the 32F period the pipe-bursting would occur.

It comes to mind that pressure reduces the melting point of ice. (ice 
skating...)
Supposing the water in the pipe was trapped by frozen plugs in both 
directions,
Could freezing at one place would raise the pressure enough that another 
place would remain liquid until 20F?
That way a percentage of the expansion-upon-freezing would be delayed.
It turns out that too much pressure is required.
13 MPa, about 130 atmospheres or 2000 psi, only reduce the melting point 
by 1 degree C or about 2 degrees F.
(http://www.lsbu.ac.uk/water/explan2.html, "11")
Your pipes would burst by 1000 psi or less, so I think you could only get 
down to 31 degrees F that way.

Some places mention that ice has "unusual compressibility",
but I do not think it is high enough to matter at the low pressures of 
pipes bursting.
The Young's modulus is 8 GPa 
(,
6x lower than salts or aluminum, but still too high to matter here.
(1/compressibility) = Bulk Modulus = 8.8 (?GPa) at
and 7.8e10 dyne/cm2 (=7.8 GPa) at 
Ice can be compressed only 0.1% at the pressure where your pipes burst,
but pipes probably stretch more like 1% before breaking,
so I do not think there is any strange compressibility of ice is delaying 
the bursting.

http://www.newton.dep.anl.gov/askasci/chem00/chem00985.htm deals with the 
density of ice too.

Good luck figuring it out.

Jim Swenson
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