Radial expansion of PVC pipe under pressure
Radial expansion of PVC pipe under pressure
(OP)
I am working on the design of a water main that will be about 500 feet long using 8 inch PVC pipe. I was wondering if there is any information about expansion of PVC pipes under pressure. Is it possible that there is some unrecognized residual storage due to pipe expansion?
Thanks,
DPAJR
Thanks,
DPAJR





RE: Radial expansion of PVC pipe under pressure
You can see some representative properties of various PVC pipe specs, here,
[white black] http://www.harvel.com/piping-pvc.asp [/color]
While you can use those properties, and those of the water (or whatever product) inside, to calculate the resultaning volume change of the water + pipe at a specific temperature and specific pressure, you will find that the restraining hoop stress of the PVC pipe as it expands under pressure will not compress the water inside to any significant degree and the volume inside the pipe at will be apx equal to the volume of water at the same temperature and pressure.
In a "long" pipe, some portion of the hoop stress expansion volume is reduced from the effects of longitudinal shortening of the pipe, Hoop Stress x Poisson ratio x length of pipe. Poisson ration for PVC is about 0.4 That shortening occurs only if the pipe is free to move in the axial direction. What is typical for a buried PVC pipe that is not securely anchored at its ends, is that from the beginning of the pipe to a point of about 150 feet away, the pipe will transition from being completely axially free to completely axially restrained, so if the pipe is over about 150 feet long and buried, it will not shorten in the axial direction due to the Poisson effect very much. If less than 150 feet, maybe only half of that thoretical shortening will actually occur.
Anyway, what that all means is that it is a very good approximation just to calculate the volume of water in your pipe at ambient temperature as equal to the equivalent volume of water at 1 atm pressure plus the change in that volume of water due to thermal expansion from 60ºF to your ambient temperature.
If pipe pressure remains high for long periods, a PVC pipe will tend to creep and permanently increase in volume. I think that it could be as much as 15-20% in some cases, but check that if you can.
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RE: Radial expansion of PVC pipe under pressure
Minor air bubbles in the line could throw your results off completely.
RE: Radial expansion of PVC pipe under pressure
INITIAL INITIAL 50 YR 50 YR
MIN MODULUS MIN MODULUS
TENSILE ELASTICITY TENSILE ELASTICITY
STRENGTH PSI STRENGTH PSI
PSI PSI
7000 400000 3700 140000
Above are listed for ribbed PVC, here at CalTrans. Also has some pretty good info and criteria for stress & buckling design, if you're interested.
http:/
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RE: Radial expansion of PVC pipe under pressure
Much data has been accumulated proving that PVC pipes, held at their pressure ratings continuously for over 100,000 hours, exhibit no perceptible rate of creep at the end of that time.
So it is very unlikely that there is some residual storage due to pipe expansion, especially with the short length of pipe that you are installing.
RE: Radial expansion of PVC pipe under pressure
Guess its only PE that creeps.
Well, smells like red herring all the way around.
Going the Big Inch!
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RE: Radial expansion of PVC pipe under pressure
ht
Going the Big Inch!
http://virtualpipeline.spaces.msn.com
RE: Radial expansion of PVC pipe under pressure
Going the Big Inch!
http://virtualpipeline.spaces.msn.com
RE: Radial expansion of PVC pipe under pressure
http://www.harvel.com/piping-pvc.asp Its in there somewhere. From what I gather, there may be some other PVC types around too, so best to check wherever you buy it.
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http://virtualpipeline.spaces.msn.com
RE: Radial expansion of PVC pipe under pressure
Thanks,
DPA