Is there a maximum to flow velocity in a pipe due to physical reasons?
Is there a maximum to flow velocity in a pipe due to physical reasons?
(OP)
I have been confronted with a principal question abouw flow velocity in a pipe. This question is not about the economical flow velocity in a pipe, that one can find in some textbooks, but about whether there is a limit flow velocity, if being exceeded, will ultimately lead to the degeneration of the pipe material. Cavitation due to a pressure lower than the local saturation pressure is a known factor, but should not be considered here.
It would be interesting to hear your comments on this.
It would be interesting to hear your comments on this.





RE: Is there a maximum to flow velocity in a pipe due to physical reasons?
RE: Is there a maximum to flow velocity in a pipe due to physical reasons?
Here's a basic discussion,
http://en.wikipedia.org/wiki/Choked_flow
**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch
http://virtualpipeline.spaces.live.com/
RE: Is there a maximum to flow velocity in a pipe due to physical reasons?
RE: Is there a maximum to flow velocity in a pipe due to physical reasons?
**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch
http://virtualpipeline.spaces.live.com/
RE: Is there a maximum to flow velocity in a pipe due to physical reasons?
Ve=c/√(pm)
Ve is erosional velocity
c= empirical constant (=100 continuous duty, =125 intermittent, and for no solids in the fluid stream)
pm = gas/liquid mixture density lbs/ft3
Higher values of "c" can be used if corrosion is not a factor.
Cheers,
John
RE: Is there a maximum to flow velocity in a pipe due to physical reasons?
RE: Is there a maximum to flow velocity in a pipe due to physical reasons?
RE: Is there a maximum to flow velocity in a pipe due to physical reasons?
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RE: Is there a maximum to flow velocity in a pipe due to physical reasons?
**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch
http://virtualpipeline.spaces.live.com/
RE: Is there a maximum to flow velocity in a pipe due to physical reasons?
http://en.wikipedia.org/wiki/Water_jet_cutter
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RE: Is there a maximum to flow velocity in a pipe due to physical reasons?
rmw
RE: Is there a maximum to flow velocity in a pipe due to physical reasons?
Uses a high velocity stream of abrasive particles suspended in a stream of Ultra High Pressure Water (30,000 - 90,000 psi) which is produced by a water jet intensifier pump.
I would like to see any ordinary pipeline exposed to these pressures. This is a specialty and is far beyond the limits of the typical design. And according to wikipedia, it is done with abrasive particles.
RE: Is there a maximum to flow velocity in a pipe due to physical reasons?
size and shape of abrasive particles in the flowing medium. So the "quality" of the fluid plays a very big role here.
A cutting process with water jets could be made even with pure water, but jet impacts the surface to be cut orthogonally, that is in a way a bit different from what a fluid does when flowing in a pipe.
RE: Is there a maximum to flow velocity in a pipe due to physical reasons?
Also, in the case of pump discharges, one must provide at least 7 diameters straight run prior to an elbow or to an expanded transition to larger diameter carbon steel piping.
RE: Is there a maximum to flow velocity in a pipe due to physical reasons?
If you are interested in further info concerning erosion related issue, you can take a glance at the attached paper.
I also insist that for pure water (no fines or abrasive particles in) erosion velocity is meaningless. Cavitation phenomena, induced in areas where the liquid pressure drops below the vapor pressure, are by far more worrying.
RE: Is there a maximum to flow velocity in a pipe due to physical reasons?
Granted, they were thin-wall "tubes" versus a pipe.
Patricia Lougheed
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RE: Is there a maximum to flow velocity in a pipe due to physical reasons?
pure water ( demineralized holy water) will erode feedwater heater tubes quickly immediately downstream of the tube inlet ( tube + tubesheet design ) for the case of AVT all volatile feedwater treatment with hydrazine type oxygen inhibitors, if the average water velocity exceeds about 10 fps ( vena contracta velocity above about 15 fps)and you are using CS tubes.
2 reasons for this- first, the fluid streamlines at the entrance cause a pronounced vena contracta increase in peak velocity ( which is also reflected in a high recirculation eddy velocity in the boundary layer at the wall) , second, the type of oxide layer formed is magnetite, which is weakly attached and will spall off easily. A better solution is to use the combined oxygenated feedwater treatment system to 250 ppb O2, and this causes the oxide scale to be a tough hematite.
RE: Is there a maximum to flow velocity in a pipe due to physical reasons?
Star for you.
Anyway are these phenomena imputable to erosion for sure? What I mean is: with heater tubes (high temperature – lower vapour pressure) and with high fluid velocity, I think cavitation plays a role and so I am not sure we can speak of simple erosion.
By the way is really hydrazine still used as oxygen scavenger? In Italy it has been banned due to carcinogen issues.
RE: Is there a maximum to flow velocity in a pipe due to physical reasons?
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RE: Is there a maximum to flow velocity in a pipe due to physical reasons?
**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch
http://virtualpipeline.spaces.live.com/
RE: Is there a maximum to flow velocity in a pipe due to physical reasons?
For cavitation, it's mostly velocity, since that's what causes the cavitation bubbles whose collapse and subsequent shockwave supposedly results in erosion.
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RE: Is there a maximum to flow velocity in a pipe due to physical reasons?
RE: Is there a maximum to flow velocity in a pipe due to physical reasons?
**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch
http://virtualpipeline.spaces.live.com/
RE: Is there a maximum to flow velocity in a pipe due to physical reasons?
Yeah. I have some difficulties (my fault) to accept the concept of erosion when dealing with a fluid which doesn't have abrasive particles or fines in.
RE: Is there a maximum to flow velocity in a pipe due to physical reasons?
**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch
http://virtualpipeline.spaces.live.com/
RE: Is there a maximum to flow velocity in a pipe due to physical reasons?
RE: Is there a maximum to flow velocity in a pipe due to physical reasons?
Like BigInch, I too have seen pipe cut through very quickly. It doesn't take much. We used to use 2" sch 80 CS elbows at the first 90 downstream of the wellhead on gas well connections. Those lasted about two months. This was gas service at 60 ft/sec, 200 deg F, and "some" sand. We switched the elbow to a tee and voila - no more cut-out problems.
RE: Is there a maximum to flow velocity in a pipe due to physical reasons?
RE: Is there a maximum to flow velocity in a pipe due to physical reasons?
The downside of this scheme is the tee creates a very short dead leg on the other end of the tee because the other end is plugged or capped. If you can't tolerate any dead legs, e.g. corrosion cells forming inside the tee, then this idea doesn't work.
RE: Is there a maximum to flow velocity in a pipe due to physical reasons?
RE: Is there a maximum to flow velocity in a pipe due to physical reasons?
RE: Is there a maximum to flow velocity in a pipe due to physical reasons?
As a chem eng/metallurgist the first part of any answer I give starts with "It Depends"
RE: Is there a maximum to flow velocity in a pipe due to physical reasons?
You say "The piping corroded away in these areas- but the root cause was the high water velocity." but I think you meant to say "the piping eroded away..." since water does not corrode copper pipe!!