Air/Water Balance in Pipe
Air/Water Balance in Pipe
(OP)
Condition:
1. 8" ID pipe is filled with air at atm
2. Pipe section is 4' long
3. Leaky valve allows water to enter section
4. Flow rate of water unknown
5. Water pressure is 100 psi
Assumption:
Water fills section until it can no longer compress the volume of air that was inside the section
Unknown:
Temperature, but pipe was underground.
Requirement:
1. To determine the pressure of the compressed air (I figure it to be 100 psi at equilibrium)
2. The amount of energy stored in the compressed air
3. Where in the section the air would be (I figure the air to occupy the top portion of the section as it is lighter)
4. A reference to support theory that when pressurized air escapes from a small opening (opening due to cutting into pipe), the rapid escape of air releases a great amount of energy and would shatter a plastic pipe
Thank you kindly in advance.
1. 8" ID pipe is filled with air at atm
2. Pipe section is 4' long
3. Leaky valve allows water to enter section
4. Flow rate of water unknown
5. Water pressure is 100 psi
Assumption:
Water fills section until it can no longer compress the volume of air that was inside the section
Unknown:
Temperature, but pipe was underground.
Requirement:
1. To determine the pressure of the compressed air (I figure it to be 100 psi at equilibrium)
2. The amount of energy stored in the compressed air
3. Where in the section the air would be (I figure the air to occupy the top portion of the section as it is lighter)
4. A reference to support theory that when pressurized air escapes from a small opening (opening due to cutting into pipe), the rapid escape of air releases a great amount of energy and would shatter a plastic pipe
Thank you kindly in advance.





RE: Air/Water Balance in Pipe
Volume of water is total volume minus that.
Longitudinal tension in the pipe will be 100 psi * pi * 4^2
Stress concentrations at each end of the cut will exceed the allowable stress causing it to rip continuously.
"I am sure it can be done. I've seen it on the internet." BigInch's favorite client.
http://www.youtube.com/watch?v=hpiIWMWWVco
"Being GREEN isn't easy." Kermit
http://virtualpipeline.spaces.live.com
RE: Air/Water Balance in Pipe
7 Jun 05 22:14 post on the thread at http://eng-tips.com/viewthread.cfm?qid=122175 , and the standard reference he cites). [See also the letter of Mr. Jack Roach of Colonial Engineering etc. at the OSHA site htt
As to your "requirement" 4, plastic pipes in general do not have much fracture toughness, nor do they have a very large flaw nor "critical crack (or damage) length" (both of sufficient size/length can cause a crack to disastrously propagate) as has been taught by BigInch. Much more information could be found with a good search engine and such keywords. Your scenario however sounds eerily familiar however to an incident I saw reported several years ago in a utility in New York, where a worker was actually killed while attempting to first cut into a particular type of plastic pipe while under pressure (obviously inadvisably!), and many other workers in many other locations have been injured and scared witless while attempting to purposefully wet tap (in and of itself a rather common practice, though in these cases with unintended explosive consequences) into the same type of pipe while pressurized. Maybe there is often a good bit of energy (and maybe even some air) present even in a good many even common water pipelines, that should be respected?
While fingers can be (and are) pointed all over the place whenever something bad happens, I noticed the near 30 year old paper at the site http://www.stormingmedia.us/79/7915/A791503.html also includes the following interesting statement from some MIT folks, "...brittle fracture properties of plastics may be of practical importance in choosing between different materials..."
RE: Air/Water Balance in Pipe
RE: Air/Water Balance in Pipe