Plastic pipes, push fit vs copper

ThisIsWeird

Section62 said:

ThisIsWeird said:

Are there any circumstances, given all other factors being equal - the level of (any) added insulation, ambient temps, temp of contained water supply, etc - that a plastic pipe will freeze before a copper one?

The honest answer would be "I don't know".  I would suggest it would be a doctoral level research project to get to the truth of the matter.  One of the complications is that the formation of ice is - to an extent - a random process, and even in two identical systems ice formation can be very different. Furthermore, repeating the experiment in the same apparatus may well give different results each time. My honest answer would also have to be, "I don't know." But I'm pretty sure - as are you :-)

Also, which pipe will freeze first in equal conditions is a different question to which pipe is more likely to freeze. Not for the practical purposes for which, I assume, this thread was made. Unless you are taking semantics to a worrying level.

I think I do get what you are saying, but that is to miss (avoid) the point of the original question - "is one pipe material less likely to freeze in the first place?" To which we can add - since it's of practical importance - "Is one material less likely to be damaged should it freeze?".

On the contrary, I addressed that in my first post in the thread.  Neither does your quote reflect the wording of the original question. My first quote does, doesn't it? I'm confused.

My first post also addressed the practicalities, and specifically the point about which system is more likely to be damaged by freezing conditions.  In my view that is far more important than the relative thermal conductivity point. Fair enough. But this discussion is about a direct comparison between metal and plastic domestic pipework, and which - if any - is less likely to freeze. That's it.

I do now accept that in the majority of real life situations, there is unlikely to be a 'significant' difference, so I retract 'significantly' from "I repeat - it is significantly less likely to freeze in the first place, and less likely to fail should it freeze". Either (any) pipe in sub-zero conditions for prolonged periods of time will freeze (simplistic, but you get what I mean). Both (all) pipes, when properly lagged, will have nigh-on identical insulation levels, so any inherent difference will be minute.

Eldi_Dos' farmer may have struck on an 'edge' case.

Section62

Eldi_Dos said:

ThisIsWeird said:

 Unless you want me to take this to the other extreme just to make a point; "If I were to lay a pipe across the sand on a beach in the Bahamas at the height of their summer, which one is..."

Do not know the science but have been told by more than one farmer/ landowner that a plastic water pipe laid quite shallow in boggy ground is not prone to freezing up even during long sub zero periods,always puzzled me.

Soil is a relatively good thermal insulator, as is ice.  It doesn't take much depth of soil to insulate a pipe reasonably well against frost, although to be sure the pipe is in a frost-free zone it needs to be much deeper.

Water has to give up a lot of heat energy to turn to ice, and the transfer of heat in the buried pipe scenario has to happen across the surface boundary between the soil and air.  As the top layer of soil starts to freeze it begins to form an insulating 'crust'.  This slows the penetration of the frost into the soil.

Also, as both grumbler and ThisIsWeird have pointed out, the flow of water in a pipe will inhibit freezing, and typically pipes in boggy ground are there to supply livestock troughs/drinkers, which tend to be used frequently and are also notoriously leaky, so it would be an unusual case where there is zero flow in the pipe.

A key point here is that wetter ground tends to be harder to freeze than drier ground - for the reason that wet ground has a larger volume of water requiring a greater total transfer of heat energy to achieve a fully frozen state.

There is another factor ThisIsWeird didn't mention, which is if the pipe has a flow of water in it at (say) 10C and the surrounding ground is slightly colder, then the pipe will have the effect of warming the ground - acting as a linear heater.  The heat energy imparted to the soil surrounding the pipe will need to escape - again, through the insulating blanket of soil and ice - which will contribute to the delay in the pipe becoming frozen as the surface temperature drops.  This would be roughly analagous to a ground source heat pump working in reverse.  Water at 10C flowing through a pipe surrounded by colder ground will be heating the ground... even though we would normally think of the water in the pipe as being 'cold'.

Section62

ThisIsWeird said:

Also, which pipe will freeze first in equal conditions is a different question to which pipe is more likely to freeze. Not for the practical purposes for which, I assume, this thread was made. Unless you are taking semantics to a worrying level.

.....

My first post also addressed the practicalities, and specifically the point about which system is more likely to be damaged by freezing conditions.  In my view that is far more important than the relative thermal conductivity point. Fair enough. But this discussion is about a direct comparison between metal and plastic domestic pipework, and which - if any - is less likely to freeze. That's it.

If the thread was made for practical purposes, then isn't the discussion of the practical reality more important than a theoretical discussion about which pipe will freeze first?

Particularly given we can't actually say which pipe would freeze first without doing some complicated maths and some clever experiments.  (E.g. how would you actually detect that the pipe is fully frozen?)

ThisIsWeird said:

My first quote does, doesn't it? I'm confused.

"Do plastic pipes freeze as easily as copper, I doubt it. If I am correct, is they a big different, EG copper would certainly freeze in an area same tp and no lagging vs a plastic pipe in the same area no lagging, ie net to each other both cold water pipes"

=/=

"is one pipe material less likely to freeze in the first place?"

ThisIsWeird said:

Either (any) pipe in sub-zero conditions for prolonged periods of time will freeze (simplistic, but you get what I mean). Both (all) pipes, when properly lagged, will have nigh-on identical insulation levels, so any inherent difference will be minute.

I agree.  This is essentially a perfect summary of the first paragraph of my first post on the thread. It has been a really interesting discussion getting here though.

ThisIsWeird

'Interesting' is one way of putting it

Gavin83

For me any indoor pipework would be copper only with soldered joints where possible or compression joints where not. No inaccessible compression though buried in walls or the like. Were it outside (such as running a water supply to an outhouse/annex) I'd use plastic. Others are of course free to do it how they wish but this is the route I'd take.

The risk of freezing pipes indoors seems so minimal it wouldn't even really be a consideration for me. However I would insulate properly. I also don't have any pipes running through my loft.

Eldi_Dos

In the situations I mentioned the plastic water pipe were feeding from main building to remote outbuildings.The pipes were dug in to correct depth on verge and when going through field (pasture) but due to lay of the land and bends in the track pipes had been laid through boggy ground shallow enough to see route with the eye.
When  I mentioned it to landowners they both ( on separate occasions) gave that wry smile and knowing look that country folk give when a city dweller asks a daft question.
The only thing I can think of is that the boggy ground is peaty and may give off a bit of heat like a compost heap will,then a coating of ice on top will keep that in and protect from air temperature.

ThisIsWeird

Eldi_Dos said:

When  I mentioned it to landowners they both ( on separate occasions) gave that wry smile and knowing look that country folk give when a city dweller asks a daft question.

Isn't that just annoying?

Fortunately, I have the solution.

Section62

Eldi_Dos said:

When  I mentioned it to landowners they both ( on separate occasions) gave that wry smile and knowing look that country folk give when a city dweller asks a daft question.

It is possible they were thinking what I was thinking when I was writing my previous post - that in freezing conditions some aquatic life will go to the bottom of a pond, if not bury itself in the muddy pond bottom, because it is warmer there than on the surface due to the insulating effects of ice and soil/mud (and water being densest at 4C).

I'd suggest it could be that kind of instinctive country-folk knowledge that wet muddy conditions are less likely to freeze to any depth compared to drier conditions.