Plastic pipes, push fit vs copper

ThisIsWeird

That's another area where plastic fittings can have problems - when used with chromed or Stainless Steel pipe. Both are far too hard for the grab rings to grip properly, and chromed pipe might also be slightly too thick. Genuine and high risk of the fittings blowing off - say if it's at mains pressure, or pipes freeze.

For chromed pipe, the chrome layer should be removed to expose the copper (that's a real pain and not worth doing), and for SS just don't use plastic fittings! For both, it's best to use brass compression fittings - and fit the correct insert for the plastic pipe.

Section62

ThisIsWeird said:

I don't recall ever having had a push-fit connection fail, either on copper or plastic pipe, provided it was done correctly.

I've seen a fair few that have failed, not due to poor workmanship.  The design of plastic push-fit fittings means they are more prone to problems with stress concentration.  Hence them potentially failing at the joint.  I understood that was what you meant in your first post about them being "split along their side seams", as one of the potential failure modes.  I've also seen circumferential cracking, possibly the more common failure mode in my experience.

ThisIsWeird said:

I repeat - it is significantly less likely to freeze in the first place, and less likely to fail should it freeze. Plastic is a much better insulator than copper*, and the wall thickness must be at least twice that of copper, perhaps x 3?

* hold a 6" piece of plastic pipe in one hand, and a matching piece of copper in the other. Stick both ends in a blow torch flame.

Can you quantify that assertion in some way?  I would (again) say the difference is marginal.

Your proposed experiment isn't realistic because it is comparing more or less instant conduction of heat at temperatures much greater than anything you would expect in ambient conditions.

Pipes typically freeze in the built environment as a result of being exposed to cold over a prolonged period of time.  I.e. a few degrees below zero over timescales of hours.

In those conditions the difference in thermal conductivity between plastic and copper plays less of a role in determining whether or not a given pipe may freeze. There may be some edge-cases where a plastic pipe may perform better in a very short period (e.g. minutes) of freezing conditions, but in fact we couldn't calculate the real-world overall probability of a pipe freezing without introducing data on the probability of different climatic conditions occuring, which in turn are location dependent.

TL;DR - there's no moneysaving point in ripping out copper piping and replacing it with plastic to reduce the risk of it freezing.  Adding good quality pipe insulation is far more important.

diystarter7

ThisIsWeird said:

That's another area where plastic fittings can have problems - when used with chromed or Stainless Steel pipe. Both are far too hard for the grab rings to grip properly, and chromed pipe might also be slightly too thick. Genuine and high risk of the fittings blowing off - say if it's at mains pressure, or pipes freeze.

For chromed pipe, the chrome layer should be removed to expose the copper (that's a real pain and not worth doing), and for SS just don't use plastic fittings! For both, it's best to use brass compression fittings - and fit the correct insert for the plastic pipe.

Hi
Thanks
From memory the chromes come off the copper.
Thanks

ThisIsWeird

Section62 said:

I've seen a fair few that have failed, not due to poor workmanship.  The design of plastic push-fit fittings means they are more prone to problems with stress concentration.  Hence them potentially failing at the joint.  I understood that was what you meant in your first post about them being "split along their side seams", as one of the potential failure modes.  I've also seen circumferential cracking, possibly the more common failure mode in my experience. I think I've only seen them fail through freezing, and the fittings split along the moulding seams. But my experience is very limited. Little doubt that a brass compression fittings is a much stronger and more reliable component.

ThisIsWeird said:

I repeat - it is significantly less likely to freeze in the first place, and less likely to fail should it freeze. Plastic is a much better insulator than copper*, and the wall thickness must be at least twice that of copper, perhaps x 3?

* hold a 6" piece of plastic pipe in one hand, and a matching piece of copper in the other. Stick both ends in a blow torch flame.

Can you quantify that assertion in some way?  I would (again) say the difference is marginal. Once insulation is added, then - yes - the difference is marginal, tho' plastic retains the added advantage of being largely able to tolerate being frozen - it'll expand to accommodate the freezing water. Bare, their insulation values are very different.

If you are suggesting that in most practical domestic situations, this difference is largely immaterial - "if it's cold enough for one to freeze, the other is 'likely' to do so too" - then you are probably right. But that is not a true comparison of the two, and dismisses their inherent differences.

Your proposed experiment isn't realistic because it is comparing more or less instant conduction of heat at temperatures much greater than anything you would expect in ambient conditions. But it does demonstrate the relative insulation/conduction properties of the two, and that is transferrable to all situations.

Pipes typically freeze in the built environment as a result of being exposed to cold over a prolonged period of time.  I.e. a few degrees below zero over timescales of hours. Of course. But again that does not diminish the fact that plastic will still have the edge, a significant one. Plastic pipe is not only a much better insulator - to put it bluntly, copper is a very poor one, and is often chosen specifically for that property - but the pipe wall thickness will be at least double. We can argue the toss about just how 'significant' this is in practical cases (and it won't be if both are properly lagged), but there will be many real-life situations where an ambient temp of just a couple of degrees 'below', coupled with a water supply temp of typically ~10oC - will make the relative freezing times of these two significantly different. And I would (again) say that, should the worst happen, one will most likely survive. Come on - you know that in many real world situations, say if the temp is just onbe ot two degrees below, and the water is at a typical ~10oC starting point - one is far more likely to freeze, and much sooner, than the other. That is all I'm saying. If your point is,

In those conditions the difference in thermal conductivity between plastic and copper plays less of a role in determining whether or not a given pipe may freeze. There may be some edge-cases where a plastic pipe may perform better in a very short period (e.g. minutes) of freezing conditions, but in fact we couldn't calculate the real-world overall probability of a pipe freezing without introducing data on the probability of different climatic conditions occurring, which in turn are location dependent. Of course. I would suggest, tho', that 'some edge cases' are actually more prevalent in the UK's environment than you may be implying. We don't tend to have hard frosts, but typically just 2, 3, or 4 degrees below. Under these conditions, I know which pipe is likely to survive the overnight freeze.

TL;DR - there's no moneysaving point in ripping out copper piping and replacing it with plastic to reduce the risk of it freezing.  Adding good quality pipe insulation is far more important. Totally agree. But, if starting from scratch, and if the risk of freezing was a prime consideration, the choice of plastic over copper is a no-brainer. Regardless of, and allowing for, plastic pipe's sheer physical convenience (long lengths, lighter, flexible), it would still be a weird person who would choose to lay copper pipe instead of plastic in a trench to supply their garden room. Yes, once insulated, the difference is marginal, but there will always remain a difference. Bare, significant.

I think I understand what you are saying - in essence, if you don't insulate both, then it's a moot point - they'll both freeze. I agree. But they are different.

Section62

ThisIsWeird said:

If you are suggesting that in most practical domestic situations, this difference is largely immaterial - "if it's cold enough for one to freeze, the other is 'likely' to do so too" - then you are probably right. But that is not a true comparison of the two, and dismisses their inherent differences.

No. My point is you are unduly focussing on one difference - thermal conductivity - and drawing an unscientific conclusion.  There are many other inherent differences between plastic pipes and copper ones which will impact on the rate of ice formation, and therefore the 'risk' of a pipe freezing.

But it does demonstrate the relative insulation/conduction properties of the two, and that is transferrable to all situations.

It would be simpler (and more accurate) to refer to typical thermal conductivity values for plastic pipe vs copper.

We could probably agree on about 20W/m.K for plastic pipe compared to around 385 W/m.K for copper.

That's a difference of roughly 20x ...but doesn't mean that a copper pipe is 20 times more likely to freeze than a plastic one.  This is the crucial point, the probability of a pipe freezing is about much more than just the thermal conductivity of the pipe material.

We can argue the toss about just how 'significant' this is in practical cases (and it won't be if both are properly lagged), but there will be many real-life situations where an ambient temp of just a couple of degrees 'below', coupled with a water supply temp of typically ~10oC - will make the relative freezing times of these two significantly different.

There could well be.  But that cannot simply be extrapolated to a general case that a plastic pipe is "significantly less likely to freeze" than a copper one

Of course. I would suggest, tho', that 'some edge cases' are actually more prevalent in the UK's environment than you may be implying. We don't tend to have hard frosts, but typically just 2, 3, or 4 degrees below. Under these conditions, I know which pipe is likely to survive the overnight freeze.

This is the 'meat' of the issue. The process of ice formation is complex, it doesn't simply happen instantly the moment water reaches 0C.  To properly understand the risk of a pipe freezing up we need to look at factors such as nucleation. We need to consider the thermal conductivity of ice because the ice itself is a good insulator. We can apply Fourier's law to work out the rate of heat transfer with the proviso we are dealing with a static situation.  In reality the conditions are unlikely to be static, not least because the ambient temperature is unlikely to change to -4C instantaneuosly.

Possibly quite importantly, we can also consider the effect of volume of water to be frozen per unit length of pipe, because the pipe wall thickness you've put on the positive side of the equation for plastic pipe also means the volume of water inside the pipe is lower, and therefore needs less total energy transfer to reach a point where the pipe is frozen solid.

Put simply, the probability of a pipe freezing is affected by many things besides the thermal conductivity of the pipe material.  It is wrong to take one factor (thermal conductivity) and state (as fact) that a plastic pipe is "significantly less likely to freeze" than a copper one.

Totally agree. But, if starting from scratch, and if the risk of freezing was a prime consideration, the choice of plastic over copper is a no-brainer. Regardless of, and allowing for, plastic pipe's sheer physical convenience (long lengths, lighter, flexible), it would still be a weird person who would choose to lay copper pipe instead of plastic in a trench to supply their garden room. Yes, once insulated, the difference is marginal, but there will always remain a difference. Bare, significant.

For the reasons given above I disagree with the "no-brainer" comment.  In addition, where the pipe isn't being used in isolation (i.e. fittings are needed) it is also necessary to consider the strength of joints.  Dismissing copper as a "no-brainer" means ruling out the use of soldered joints - which may - in some situations be the most critical factor in terms of resistance to frost/cold.

Burying copper pipe in a trench in the ground to supply a garden room would be "weird" - but the principal reasons for that shouldn't include the relative probability of plastic pipes freezing in comparison to copper ones.

Edit: Typo

ThisIsWeird

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?

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?".

Forget 'joints', added insulation levels, et al. 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..."

Section62

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.

Also, which pipe will freeze first in equal conditions is a different question to which pipe is more likely to freeze.

ThisIsWeird said:

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 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.

ThisIsWeird said:

Forget 'joints', added insulation levels, et al. 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..."

Bahamas?  What is really needed here is a spherical pipe in a vacuum.

Eldi_Dos

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.

diystarter7

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.

Hi

Could it be it is constructed with a slightly different material?

Metal is always a lot colder to touch, EG galvanised rails are freezing in cold weather but lick of paint not as cold
Thanks

ThisIsWeird

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.

IF that's a largish MDPE pipe - which will have wall thicknesses of around 3mm - and IF the farmer still makes regular use of the pipe, sending water down it once a day or so, then that could be one of the situations where plastic pipe has the 'edge' over copper.

The water passing through will likely be at ~10oC, or a little below this, and will be of a sizeable volume (25mm pipe?). So even if the frost penetrates down that far (and it easily will, of course), there might be enough inherent insulation in the pipe to allow that water to remain largely above freezing. If the farmer uses that pipe on a regular basis, then the near-freezing water will be replenished.

However, if just left with no new flow, that pipe is surely bound to freeze?