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Pipe Bursting


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Pure water is unusual in that its minimum volume occurs at about 4 degrees C.

It will expand at temperatures both above and below this.

In an ice covered pond the temperature at the deepest part is usually about 4 degrees C which helps creatures such as frogs to survive.

Edited by TonyMcC
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Pure water is unusual in that its minimum volume occurs at about 4 degrees C.

It will expand at temperatures both above and below this.

In an ice covered pond the temperature at the deepest part is usually about 4 degrees C which helps creatures such as frogs to survive.

 

Yeah, without this very unusual property of water the world as we know it would be very different.

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  • 4 weeks later...

A related topic is crushing of piping due to underpressure, i.e. a buckling phenomenon. In some cases, pipes collapse due to underpressure, for example when steam condensates into water. Theoretically, a similar mechanism could cause large compressive hoop stresses in a pipe when the water is contracting..

 

Otherwise, I agree. Thermodynamic properties of water = good for frogs! :)

 

 

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A related topic is crushing of piping due to underpressure, i.e. a buckling phenomenon. In some cases, pipes collapse due to underpressure, for example when steam condensates into water. Theoretically, a similar mechanism could cause large compressive hoop stresses in a pipe when the water is contracting..

 

Otherwise, I agree. Thermodynamic properties of water = good for frogs! :)

 

Baxtrom, I would like some further explanation. It seems to me that a pipe made of a material with high tensile strength, but little else, such as a water hose would collapse easily when interior pressure is reduced, but because air pressure is only about 15 psi, a rigid pipe that is able to contain 15 psi internal pressure should easily be able to withstand this amount of external pressure if it were completely evacuated. SM

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Baxtrom, I would like some further explanation. It seems to me that a pipe made of a material with high tensile strength, but little else, such as a water hose would collapse easily when interior pressure is reduced, but because air pressure is only about 15 psi, a rigid pipe that is able to contain 15 psi internal pressure should easily be able to withstand this amount of external pressure if it were completely evacuated. SM

 

Actually, a large-diameter pipe or pressure vessel can typically hold much greater internal overpressure than underpressure. This is because of elastic instability, which can arise when compressive forces become too large. It's similar to buckling of a slender column under axial compression. When a pipe or pressure vessel is subject to underpressure, compressive hoop stresses build up in the wall of the vessel. If they become too large.. :P

 

image1.jpeg

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Baxtrom. I was thinking about a typical home owner's water pipe. Your tank photograph looks to be a pretty good illustration of my water hose example. I would bet somebody got in trouble for that one. SM

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Not exactly the water pipe, but my mother in law (no jokes please she is no longer alive) several years ago had her hot water tank collapse inwards. She had been away from home in freezing weather and the feed to her tank, which was in the loft, had frozen. She turned on the hot tap and as water flowed from the tank the tank just collapsed. Quite powerful stuff air pressure!

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Not exactly the water pipe, but my mother in law (no jokes please she is no longer alive) several years ago had her hot water tank collapse inwards. She had been away from home in freezing weather and the feed to her tank, which was in the loft, had frozen. She turned on the hot tap and as water flowed from the tank the tank just collapsed. Quite powerful stuff air pressure!

 

 

Sounds like buckling!

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TonyMcC, although the pressure relief valve on a hot water tank is set at 160psi they are pressure tested to 320 psi. These tanks are made of steel and normally would not collapse from air pressure. Pressure tanks in domestic water systems are subjected to an internal vacuum much more frequently than one might guess, and are designed appropriately. Your collapsed tank could have been seriously damaged by freezing, or it was rusted out. SM

Edited by SMF
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TonyMcC, although the pressure relief valve on a hot water tank is set at 160psi they are pressure tested to 320 psi. These tanks are made of steel and normally would not collapse from air pressure. Pressure tanks in domestic water systems are subjected to an internal vacuum much more frequently than one might guess, and are designed appropriately. Your collapsed tank could have been seriously damaged by freezing, or it was rusted out. SM

Maybe, but this tank was made of copper and on entering her house she attempted to run water before lighting her solid fuel boiler trying to make sure water could flow through the system. On the typical UK system there is not a pressure relief valve, but instead there is an expansion pipe feeding back to a header tank in the loft. The water in this pipe must also have been frozen. It is fortunate that she hadn't lit the boiler which could have caused an explosion.

post-22702-0-41654500-1304446673_thumb.jpg

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TonyMcC, your diagram has me very confused. It appears that the water tap that was opened was above the water tank and the only pressure on this system was only a few feet of water above the tap. I don’t see how a vacuum could have formed in the tank at all from opening the tap.

 

John Cuthber, any of us can only comment on what we know about when there is no country or standard specified. I am pretty sure that the depicted system is not common in 95% of the world, and I am very sure that any responsible plumbing contractor in the US would run screaming from this one for good reason.

 

SM

 

 

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  • 3 weeks later...

TonyMcC, your diagram has me very confused. It appears that the water tap that was opened was above the water tank and the only pressure on this system was only a few feet of water above the tap. I don’t see how a vacuum could have formed in the tank at all from opening the tap.

 

SM

Sorry for the late reply, but I have only just seen your post. Two facts exist, the tank did collapse and the house had been empty for some time in freezing weather. My diagram only shows one tap, but of course there are a few, some being upstairs and some being downstairs. The tank itself is upstairs. I imagine the cold water feed to the tank was frozen and opening a downstairs tap caused the tank to start emptying through syphonic action. I was not at the house at the time, just the receiver of a very distressed phone call. The people called in to do the repair put the damage down to parts of the system being frozen.

 

I believe most systems in the UK are still similar to the system shown. It has been only over relatively recent years that sealed systems have come into favour. In my own home I had a new sealed system with a "combi" boiler fitted about ten years ago. It was considered very modern!

 

later edit:- you got me wondering about just how this happened and whether it is common. I attach an excerpt from the following web page http://www.diybanter.com/uk-diy/8548-re-ch-expansion-pipe-vents-into-cold-cistern.html

post-22702-0-23156600-1305822396_thumb.jpg

Edited by TonyMcC
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"I am very sure that any responsible plumbing contractor in the US would run screaming from this one for good reason."

Why? after all, it works perfectly well in millions of homes (including mine).

 

You seem to have proved my point by tacitly asserting that the US system is the best, without any supporting evidence.

Edited by John Cuthber
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"I am very sure that any responsible plumbing contractor in the US would run screaming from this one for good reason."

Why? after all, it works perfectly well in millions of homes (including mine).

 

You seem to have proved my point by tacitly asserting that the US system is the best, without any supporting evidence.

I'm not sure that the statement of one person proves your implication (below) that Americans are stupid. <_<

 

( Note for Americans, 95% of the world do not live in America and may do things differently.)

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he's not implying americans are stupid, he is implying they have a very US centered world view. which is generally correct as witnessed in more than one study and general conversations over the internet.

 

now, it's true that not every person from the US has this world view but its definitely a large (>20%) proportion.

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As evidence I cite this

http://xkcd.com/850/

and then, of course, I have to backtrack on the idea that Americans can't use irony. :D

 

 

In any event, the coefficient of expansion of copper is something like 20 ppm per degree. When water freezes it expands by about 10% i.e. about 100,000 ppm.

The shrinking copper isn't the important thing.

Edited by John Cuthber
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I'm not sure what are pipes are usually made of, but carbon steel pipes are brittle at low temperature, see what happen to Titanic, the ship got divided into two parts when getting hit with iceberg.. :o the rising pressure inside the pipe due to freezing water should be the second reason of the failure.

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