PVC pipe absolute roughness
PVC pipe absolute roughness
(OP)
What is the typical absolute roughness, in mm, of typical PVC pipe having an inside diameter of, say, 15 to 75 mm? Thanks.
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PVC pipe absolute roughness
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PVC pipe absolute roughnessPVC pipe absolute roughness(OP)
What is the typical absolute roughness, in mm, of typical PVC pipe having an inside diameter of, say, 15 to 75 mm? Thanks.
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RE: PVC pipe absolute roughness
If you are talking about spiral wound PVC hose then that is something completely different and pressure drops are much higher.
Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com
RE: PVC pipe absolute roughness
RE: PVC pipe absolute roughness
See attached link - Chapter 6, TABLE 1-4, on page 165.
http://pl
RE: PVC pipe absolute roughness
For above link, see Errata Sheet for page 165 (link attached.)
http://plasticpipe.org/pdf/pe_handbook_errata.pdf
RE: PVC pipe absolute roughness
For a 15 mm pipe with water at a velocity of 2 m/s the two different roughnesses result in a 4% difference in the predicted pressure drops. The difference increases to 20% at a velocity of 6 m/s.
In a 75 mm pipe the differences would decrease to 2.5% and 5.5% for the 2 m/s and 6 m/s cases.
This is an example of where it is actually a good idea to go back to the old fashioned way of doing calcs by hand and by using charts. If the relative roughnesses are plotted on a standard Moody Diagram you can clearly see the low impact of roughness on your calculation. Using a computer masks this information.
Digging a little bit deeper into the above data provided by the Plastic Pipe Institute illustrates how difficult it is to find reliable design data. In the middle of Table 1-4 on Page 165 drawn tubing is stated to be the same as "smooth pipe" with a roughness of 0.000005 ft (=0.00006" or 0.0015mm). At the bottom of the same table "smooth pipe" is defined as having a roughness of 0.00001" (=0.00025mm). If there is a factor of 6 variation in data in the same table, we must expect variances between data from different sources.
On balance, I would stick with my design value of 0.005 mm.
Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com
RE: PVC pipe absolute roughness
RE: PVC pipe absolute roughness
Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com
RE: PVC pipe absolute roughness
Katmar is basically correct in what he is telling you. Let me make 2 additional points. Firstly, the absolute roughness of the pipe material is not the appropriate parameter to be used for commercial pipes in the friction factor equation. While the absolute roughness was instrumental in framing the pipe flow equations using experimental pipes, it was found in practice that additional factors such as pipe geometry (e.g. ovality), pipe joints, gradual bends due to misalignments of pipe sections, etc also cause pressure drop. In PE piping, the internal bead caused by fusion joints can counter balance the benefit of having a smooth pipe interior surface.
The appropriate parameter is the "effective roughness" which is determined by back calculating the roughness term, e, in the rough pipe law using field data. If you go back to the experimental reports on commercial pipelines, you'll see that they determined pipeline roughness by back calculation even if they didn't call it "effective roughness." For plastic pipe, it is difficult enough to find any roughness data, let alone effective roughness data.
The second point is regarding the classification of pipe as "smooth". The PE Handbook says "Pipes that have absolute roughness equal to or less than 0.00001inch are considered to exhibit "smooth pipe" characteristics." This is nonsense (although I do have a high regard for the PE Handbook as a whole.) Smooth pipe flow is not a characteristic of the pipe. Smooth pipe flow refers to hydraulically smooth, a condition that exists when the flow is partially turbulent and dependent only on the Reynolds number (not on surface roughness). Smooth pipe flow can exist in any kind of pipe so long as the Reynolds number is below a certain critical value. As a rule, smooth pipe flow will persist longer in pipes with smaller a effective roughness.
In conclusion, I would say that, for design purposes, you should go with the roughness value Katmar suggested.
RE: PVC pipe absolute roughness
Therefore, if anyone who sees this thread ever has any additional input regarding my above questions, all information would be very greatly appreciated. Thanks to all who have contributed thus far.
RE: PVC pipe absolute roughness
http://virtualpipeline.spaces.msn.com
"What gets us into trouble is not what we don't know, its what we know for sure" - Mark Twain
RE: PVC pipe absolute roughness
It can make a real difference in miles of HDPE or spoolable composite, but I've never heard of anyone running enough PVC in a row to make a difference.
David
RE: PVC pipe absolute roughness
http://virtualpipeline.spaces.msn.com
"What gets us into trouble is not what we don't know, its what we know for sure" - Mark Twain
RE: PVC pipe absolute roughness
David
RE: PVC pipe absolute roughness
http://ww
RE: PVC pipe absolute roughness
As a matter of fact, I am however aware of some multiple head loss measurements etc. in actual flow tests of three working pvc pipelines (though in those particular cases the pipes were all a good bit larger diameter than what you are asking about). It is my understanding that multiple runs/flow tests of 12" pvc pipelines in the communities of Blackwood, NJ and Dothan, AL, as well as of another 18" pvc pipeline in Wister, OK were conducted a few years ago by DIPRA P.E.'s working with the interested utilities involved. In that testing, I believe head losses, flows, and pipe data (C900/905)/etc. were measured that back-calculate under the circumstances to absolute roughnesses in the range of
0.00032-0.00050 ft (0.0038-0.006 inches or 0.13-0.15 mm) for those working pvc pipelines. I suspect interested parties could probably get the actual measured head losses, pipe data and flows etc., if they wished to do their own back-calculations from DIPRA, as I believe these results have been published in different forms over the years.
I do not know why there is otherwise a dearth of published data concerning head losses in actual working plastic pipelines; however, I do know that plastic materials have much lower allowable hoop tensile stresses than metal pipes, of course requiring thicker walls to carry normal design pressures with some degree of dependability. With all else being equal (and irrespective of all the other pertinent variables vzeos mentioned, and perhaps more), thicker plastic pipe walls of course can mean a significantly smaller internal flow diameter for a given outside diameter pipe. Thus, it would appear the plastics industry could be under a great deal of pressure (so to speak) to claim that the pipe wall is extremely smooth, so as to at least on paper partially off-set the known flow advantage of some larger inside diameter, modern metal pipes.
It would appear however that the factor with by far the most significance (at least with regard to reasonably smooth, modern pipes) is the pipe inside diameter, and the users may otherwise use extremely (or outrageously?) smooth assumed values for field pipe wall roughness perhaps mostly at their own risk (see the hydraulic program that can be utilized to compare such effects, "Hydraulic Analysis of Ductile Iron Pipe " et al available from http://www.dipra.org/ , and the references to the aforementioned flow testing on page 12 of the publication http://www.dipra.org/pdf/DIPvsPVC.pdf ). . .