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RAT 5
6th Mar 2018, 18:53
I'm confused. Physics lectures were too long ago, and practical has replaced theory.
I always thought pipes burst when frozen. Watching the BBC, SE water has shut off supply to repair underground pipes that have burst during the thaw. As the supply continued in the frozen days I would assume the pipes had not frozen and become blocked. So how does the thaw burst the pipes?
A spokesman said it was the fault of the extreme cold snap of recent. It ain't the first time the Siberian wind has blown severe cold over UK. And to get to UK, guess what, it crosses many countries that do not have burst pipes underground in the cold or the thaw.

So what is the truth?

Pontius Navigator
6th Mar 2018, 19:04
RAT, agree, it was perceived wisdom that running water was warm enough not to freeze. Clearly if they did freeze then maybe the thaw would burst them.

Possibly there were vulnerable water pipes were water was not drawn regularly, say a factory closed for the weekend. Or could the freeze have crushed the pipes and the thaw allow them flood?

VP959
6th Mar 2018, 19:23
Pipes don't necessarily burst when they freeze.

The worst case is when pipes freeze and block flow either side of a non-frozen section, and when the non-frozen section then cools to the maximum volume temperature of 4 deg C, then the pressure in the pipe will be at it's maximum and might be enough to exceed the pressure rating of the pipe.

Pontius Navigator
6th Mar 2018, 19:43
Pipes don't necessarily burst when they freeze.

The worst case is when pipes freeze and block flow either side of a non-frozen section, and when the non-frozen section then cools to the maximum volume temperature of 4 deg C, then the pressure in the pipe will be at it's maximum and might be enough to exceed the pressure rating of the pipe.I recall cast iron drain pipes freezing and huge icicles from our gutters. After the thaw some cast iron pipes had split.

Sallyann1234
6th Mar 2018, 20:38
As VP says, the maximum volume is at +4C, which doesn't matter as the temperature goes down because there is no blockage.
As the temperature increases from below freezing there is no room for the expansion.
The modern replacement of subsoil pipes with polypropylene generally avoids bursts, because they are more able to expand.

NutLoose
6th Mar 2018, 20:43
I thought it was the freezing that splits them as ice expands, the thaw just exposes them

MFC_Fly
6th Mar 2018, 20:48
Exactly NutLoose, the freezing breaks the pipes, but since the water is frozen it doesn't flow. It is only when it returns to its liquid state does the break become obvious with water p!$$ing everywhere :ok:

DType
6th Mar 2018, 21:38
It was cold enough in the frozen South to freeze UNDERGROUND pipes??????????????

ExSp33db1rd
6th Mar 2018, 21:58
Exactly NutLoose, the freezing breaks the pipes, but since the water is frozen it doesn't flow. It is only when it returns to its liquid state does the break become obvious with water p!$$ing everywhere

As I once discovered, or rather was advised by a neighbour watching water pour out of my front door when I was on the other side of the World.

MReyn24050
6th Mar 2018, 22:30
Exactly NutLoose, the freezing breaks the pipes, but since the water is frozen it doesn't flow. It is only when it returns to its liquid state does the break become obvious with water p!$$ing everywhere :ok:

Then surely who ever is down stream of that pipe/water main would not be getting a supply of water when frozen so how come they did not alert the supplier so some sort of action could be taken before the thaw set in? Just a thought!

Octane
6th Mar 2018, 23:12
What sort of action do you suggest?

Pontius Navigator
7th Mar 2018, 07:06
MR, as I said earlier, some buildings downstream may have been shut down.

DType, indeed, the pipes should be deep enough, especially in that urban heat island.

I suppose it might be land heave due to freezing and thawing rather than the pipes alone.

obgraham
7th Mar 2018, 07:17
Fill a plastic coke bottle with water, cap it, and put it in your freezer. You’ll soon see why the pipes burst. It’s the expansion of the ice volume.
All Canucks know this!

treadigraph
7th Mar 2018, 07:35
Fill a plastic coke bottle with water, cap it, and put it in your freezer. Youíll soon see why the pipes burst. Itís the expansion of the ice volume.
All Canucks know this!

My sister did that with a bottle of wine.

Bit grumpy this morning; got home at 1240am after training breakdown at selhurst. Then awoken before 4am by thames water digging up the road outside, presumably to fix a leak. To be fair they'd finished the job by 7am but I feel totally knackered...

RAT 5
7th Mar 2018, 10:05
So we are back to 'the truth'. A pipe 5' underground; would it freeze? If it did then someone down stream would not have any water, but there were no alerts. Thus one can assume water was flowing. Cadburys, one of the victims, would not shutdown in weekends; I'd expect them to run 24/7 on automated production. Their supply was shut off during the thaw.
It just doesn't seem correct, and living outside UK, where the severity is worse and more common and does not cause problems, it seems a UK thing. To blame it on an unprecedented cold snap seems very lame.

Dont Hang Up
7th Mar 2018, 12:44
So we are back to 'the truth'. A pipe 5' underground; would it freeze? If it did then someone down stream would not have any water, but there were no alerts. Thus one can assume water was flowing. Cadburys, one of the victims, would not shutdown in weekends; I'd expect them to run 24/7 on automated production. Their supply was shut off during the thaw.
It just doesn't seem correct, and living outside UK, where the severity is worse and more common and does not cause problems, it seems a UK thing. To blame it on an unprecedented cold snap seems very lame.

So what would you blame it on exactly?

Having just experienced nearly four days without water in North Pembrokeshire, I feel allowed a certain irritation with the water company (Welsh Water), but primarily because of the poor quality and infrequent update of their information to their customers, and delays in getting bowsers and bottled water into place.

In terms of the actual failures I would spare them your scepticism. Yes, our water flowed fine during the freeze. Then, within hours of the thaw setting in, the pressure dropped steadily - soon to be non existent.

The mechanism is this: Mains to outlying 'end of the line' regions freeze and burst due to lack of flow. Pipes in unoccupied residences and businesses freeze and burst. Also I understand that some mains supplies have a ring design so a freeze at a point of minimum flow may go unnoticed because supply comes from each end. Then the thaw occurs and the water company finds it is pumping unprecedented quantities of water into the system whilst the phone lines light up with ever increasing numbers of people complaining of low pressure or no supply.

To perfectly illustrate the point, an unoccupied holiday home adjacent to us started to gush forth water from under the front door almost immediately the supply to the area was restored. Trying to restore the supply in these conditions must be a little like trying to fill a colander.

NutLoose
7th Mar 2018, 13:16
I was lucky, I came back a couple of years ago from Holiday when it was freezing, I just happened to look in the downstairs toilet and the gland seal on the pipe to the sink had gone, the resulting vertical icicle had pushed the flexible pipe up, I turned off the supply to it, leggged it to local Focus DIY store, bought new glands, cut the icicle off flush, replaced the gland with new, refitted the pipe, turned the tap on and left it to warm up, result, the ice cleared, water in pipe came out of tap and down the plug hole and supply was restored. I turn it off now when not in use.

Windy Militant
7th Mar 2018, 22:22
A pipe 5 foot under ground would be OK, problem is that contractors paid to put pipework in don't always do that.
Last big freeze we had I had to do a regular water run over to my mums friend because the new main that had been installed that summer froze up and didn't thaw out for about four days because it was only a few inches sub surface rather than a few feet.
However there are more of the primary mains failing like the 2015 failure at the Llechryd extraction plant. You can only add so much demand onto the system before things start weakening and then add some extra strain with the freezing weather and bang.
One wonders with all this new house building where the water is going to come from as the developers seem to think it's OK to tap into existing services without investing in additional infrastructure to service the new demand.

treadigraph
7th Mar 2018, 22:28
Bloody Thames Water crew are just up the road - please no nocturnal drilling...

One wonders with all this new house building where the water is going to come from as the developers seem to think it's OK to tap into existing services without investing in additional infrastructure to service the new demand.

Conversion of office blocks to residential in Croydon, plus lots of new build high rise - same question, plus leccy, gas, NHS, education, public transport ("easy commute to Victoria, London Bridge, Canary Wharf" - the trains are already rammed when they arrive to East Croydon...)

sitigeltfel
8th Mar 2018, 06:16
The point at which water freezes depends on the pressure applied.

Krystal n chips
8th Mar 2018, 06:32
So we are back to 'the truth'. A pipe 5' underground; would it freeze? If it did then someone down stream would not have any water, but there were no alerts. Thus one can assume water was flowing. Cadburys, one of the victims, would not shutdown in weekends; I'd expect them to run 24/7 on automated production. Their supply was shut off during the thaw.
It just doesn't seem correct, and living outside UK, where the severity is worse and more common and does not cause problems, it seems a UK thing. To blame it on an unprecedented cold snap seems very lame.

The word "unprecedented " has been liberally used by several organisations in recent days....it's the same as "lessons will be learned" when it comes down to public appeasement. Quick, convenient and uttered in the hope all will be forgotten as soon as possible in the minds of the gullible.

Dont Hang Up
8th Mar 2018, 06:42
The point at which water freezes depends on the pressure applied.

True in principle, but insignificant until well beyond 100 times atmospheric pressure.

Pontius Navigator
8th Mar 2018, 07:14
The point at which water freezes depends on the pressure applied.

If you take a bottle of beer out if the freezer it may be liquid at -18 and under pressure. When the cap was removed we had instant ice and a small release of liquid.

Not sure if a similar phenomenon could apply in a water pipe.

llondel
9th Mar 2018, 01:59
I woke up one morning and discovered the water pressure was almost zero. I happened to look out front and there were the water board chaps in a hole in the ground just on the downstream side of our driveway.