Velocity limitation in water pipes
Velocity limitation in water pipes
(OP)
Hello all,
My hydraulic analysis indicate that due to high available static heads, the water velocity in a relatively short (~50 m) 8" pipe occasionally reaches velocities as high as 15 - 20 m/s. My understanding is that such high velocities could lead to excessive noise, high erosion rates, and even large piping loads; therefore, have to be limited but I do not know to what value. I was wondering if someone could help me out with this issue with reference to a code, standard, or a guideline.
For your information, so far, my research has indicated that according to section 2.3 of API RP14E and page 33.3 of 1997 ASHRAE Fundamentals Handbook , in order to minimize cavitation and erosion, the flow velocity should not exceed 15 ft/s.
Thanks in advance,
Pirooz
My hydraulic analysis indicate that due to high available static heads, the water velocity in a relatively short (~50 m) 8" pipe occasionally reaches velocities as high as 15 - 20 m/s. My understanding is that such high velocities could lead to excessive noise, high erosion rates, and even large piping loads; therefore, have to be limited but I do not know to what value. I was wondering if someone could help me out with this issue with reference to a code, standard, or a guideline.
For your information, so far, my research has indicated that according to section 2.3 of API RP14E and page 33.3 of 1997 ASHRAE Fundamentals Handbook , in order to minimize cavitation and erosion, the flow velocity should not exceed 15 ft/s.
Thanks in advance,
Pirooz





RE: Velocity limitation in water pipes
Based on erosion/ corrosion issues for CS pipe , max steady, local velocity should not exceed 20 fps incuding effect of vena contracta at the inlet or near orifces. That could be increased to 30 fps with 1% chrome alloy pipe, and 75 fps for incolnel or SS pipe.
The "economic pipe size" for process costs that include pump power consumption is roughly 10 fps average or nominal velocity at full load for water systems .
For pipes feeding pumps with NPSH issues ( saturated liquid), a 5 fps design velocity may be used, but that may be increased to account for dynamic effects to avoid flashing in the downcomer during pressure transients.
2 phase flow , compressible flow, waterhammer cases involve other criteria.
RE: Velocity limitation in water pipes
Thanks for your reply. Do you know of any references for the first part of your response?
Piroz
RE: Velocity limitation in water pipes
If it ain't broke, don't fix it. If it's not safe ... make it that way.
RE: Velocity limitation in water pipes
Reasonable Velocities for the Flow of Water through Pipe:
Boiler Feed.............8 to 15 ft/sec
Pump Suction ............4 to 7 ft/sec
General Service.........4 to 10 ft/sec
City.......................to 7 ft/sec
Transmission Pipelines...3 to 5 ft/sec
Go to a basic hydraulics book. Try Cranes Technical Paper 410 as a reference for the above velocities.
http://www.eng-tips.com/viewthread.cfm?qid=111206
http://www.amazon.com/Fluids-Through-Valves-Fittin...
RE: Velocity limitation in water pipes
v(max)=100 ft/sec / (ρ)^0.5
With ρ in lbm/ft^3. I know it is ugly and that the units don't work out, but that is the published empirical equation. For water (ρ=62.4 lbm/ft^3) it works out to 12.6 ft/sec (3.9 m/sec). A lot of people round that up to 15 ft/sec. There is so much safety factor built into the constant that rounding it up to 20 ft/sec would be unlikely to lead to an increased incidence of failure.
David Simpson, PE
MuleShoe Engineering
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
RE: Velocity limitation in water pipes
I agree with bimr: Crane's Technical Paper 410, Flow of Fluids is relatively inexpensive and a good place to start. If you're going to be working with water piping, it's worth buying a copy. Besides from Amazon, you can get it direct from Crane (or their distributor): http://www.flowoffluids.com/
Patricia Lougheed
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RE: Velocity limitation in water pipes
I would like to add that I am dealing with an intermittent service; something that is barely touched in any code, standard, or guideline.
Is 15 m/s fine for such services? That is what I am not sure of.
Cheers,
Pirooz
RE: Velocity limitation in water pipes
You should be able to get about 2300 gallons per minute (velocity 15 ft/sec or 5 m/sec). As a point of reference, an 8-Inch fire hydrant puts out approximately 1500 gallons per minute.
RE: Velocity limitation in water pipes
RE: Velocity limitation in water pipes
If it ain't broke, don't fix it. If it's not safe ... make it that way.