Tek-Tips is the largest IT community on the Internet today!
Members share and learn making Tek-Tips Forums the best source of peer-reviewed technical information on the Internet!
-
Congratulations LittleInch on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!
reference standard for max permissible velocity in concrete pipes 1
- Thread starter mdrehansk
- Start date
I'm not sure you'll find an "international standard." There are many local standard documents, most of which are very similar.
Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -
Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -
- Thread starter
- #4
in USA & Canada :
for sewer pipe (low-head pressure according to ASTM C76): ACPA - American concrete pipe association - Concrete pipe design manual (see attached chapter)
for pressure pipe (according to AWWA C300 - C301 - C302 Standards) : AWWA M9 - American water works Association - Manual M9 (see attached chapter)
for sewer pipe (low-head pressure according to ASTM C76): ACPA - American concrete pipe association - Concrete pipe design manual (see attached chapter)
for pressure pipe (according to AWWA C300 - C301 - C302 Standards) : AWWA M9 - American water works Association - Manual M9 (see attached chapter)
Q: What is the maximum flow velocity I can design RCP without cavitation?
A: Velocity, by itself, does not create problems for concrete pipe within the ranges normally encountered. At velocities up to 40 feet per second, the severity of velocity-abrasion effects depends upon the characteristics of the bed load.
Please respond with the purpose of the inquiry.
A: Velocity, by itself, does not create problems for concrete pipe within the ranges normally encountered. At velocities up to 40 feet per second, the severity of velocity-abrasion effects depends upon the characteristics of the bed load.
Please respond with the purpose of the inquiry.
LittleInch
Petroleum
maximum velocity of what?
Clean water?
dirty water?
water with sand in it?
something else hard in it?
Slurry?
Gas or air?
Makes a big difference and because there are so many variables, all you will find are guides and recommendations.
Similarly pipe is usually good to high velocities, but bends and tees are subject to much more wear and need more care / reduced velocities
This isn't usually a material issue, but an economic / power one.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
Clean water?
dirty water?
water with sand in it?
something else hard in it?
Slurry?
Gas or air?
Makes a big difference and because there are so many variables, all you will find are guides and recommendations.
Similarly pipe is usually good to high velocities, but bends and tees are subject to much more wear and need more care / reduced velocities
This isn't usually a material issue, but an economic / power one.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
-
1
- #8
The first reference I can remember to the "40 fps" mentioned earlier on this thread goes back decades, at least to "Design and Construction of Sanitary and Storm Sewers" (WPCF Manual No. 9 or ASCE MOP #37, 1982 and maybe even before). The specific quote then read as follows:
"For clear water in hard-surfaced conduits, the limiting velocity is very high. Velocities in excess of 40 fps (12 m/sec) have been found harmless to concrete channels." (It is not stated whether those were actually somehow measured velocity, or back-calculated from someone's slope and formulae assumptions I will note however that that phrase was followed immediately in that manual by:
"Erosion of inverts may result from much lower velocities when sand or other gritty material is carried." [It then goes on to say that in continuous high velocity flow conditions where grit erosion is expected to be a problem the limiting velocity often is taken to be about 10 fps (3 m/sec)].
Also, if the application is pumped pressure piping I think you will find out very quickly as others have stated (at least with any proper engineering analysis, of pumping power/energy consumption and cost etc) that very high flow velocities are generally/likewise neither economical, nor in the modern Engineering lexicon “sustainable” in life cycle terms.
While it might be perceived the risk of high velocities or slopes in piping is primarily damage to lining, there are other risks or pitfalls mentioned in many past threads on these forums e.g. I believe quite significant among them is that high velocities in liquid pipelines, and particularly in large sized lines where concrete pipe is sometimes applied, mean that there is a great deal of momentum energy involved in the flow, and arguably more risk of damaging transients/water hammer(see comment of BigInch in aforementioned thread) and water column separations etc. If the application is concrete pressure piping, where the heart of the pressure containment consists of small rods or wires under high tension and covered by only shallow mortar cover on the outside layer of the pipe (the mortar coating of low tensile strength or strain, and either not, or not as effectively, pre-compressed as the inner core), due to low or no real safety factor vs same it really doesn’t take much of a surge or overpressure condition to crack the coating and thereby quite jeopardize pipe (if it was not vulnerable before). I noticed that in the public report available from the Water Research Foundation at that at least a few dozen of the reported large diameter concrete pipe failures tabulated by these experts were apparently attributed to “surge” (with several times that number simply bursts and/or corrosion etc, with no more information supplied).
In any case, concrete pipe with thin/small pressure containing components (meaning higher strain, less reserve) may well be less robust than some other pipes from the standpoint of surge. This is effectively summed up in the paragraph on "How pccp fails" on page 86 as, "In other words, there is a cascading effect: overpressure > coating cracks > wires exposed to water > wires corrode and break > pressure is transferred to the cylinder > core cracks > cylinder is exposed to water > cylinder corrodes and fails." (I would only add that if coating is also exposed to air at any time, carbon dioxide can also enter coating cracks and carbonate the mortar that was intended to protect the wires/rods.)
[Given the brevity of the information provided in the OP, and while high velocities in general may be kind of hard to avoid at least at some point in the life cycle of all pipelines, I fear the only short but reasonably accurate answer to this question may be, “It depends” (and agree with bimr, and erstwhile tag line of LittleInch to effect that more info on these forums might beget better answers – might even add a corollary that brief, open ended inquiries or fishing expeditions might on the other hand beget fish stories or fishy answers!)]
"For clear water in hard-surfaced conduits, the limiting velocity is very high. Velocities in excess of 40 fps (12 m/sec) have been found harmless to concrete channels." (It is not stated whether those were actually somehow measured velocity, or back-calculated from someone's slope and formulae assumptions I will note however that that phrase was followed immediately in that manual by:
"Erosion of inverts may result from much lower velocities when sand or other gritty material is carried." [It then goes on to say that in continuous high velocity flow conditions where grit erosion is expected to be a problem the limiting velocity often is taken to be about 10 fps (3 m/sec)].
Also, if the application is pumped pressure piping I think you will find out very quickly as others have stated (at least with any proper engineering analysis, of pumping power/energy consumption and cost etc) that very high flow velocities are generally/likewise neither economical, nor in the modern Engineering lexicon “sustainable” in life cycle terms.
While it might be perceived the risk of high velocities or slopes in piping is primarily damage to lining, there are other risks or pitfalls mentioned in many past threads on these forums e.g. I believe quite significant among them is that high velocities in liquid pipelines, and particularly in large sized lines where concrete pipe is sometimes applied, mean that there is a great deal of momentum energy involved in the flow, and arguably more risk of damaging transients/water hammer(see comment of BigInch in aforementioned thread) and water column separations etc. If the application is concrete pressure piping, where the heart of the pressure containment consists of small rods or wires under high tension and covered by only shallow mortar cover on the outside layer of the pipe (the mortar coating of low tensile strength or strain, and either not, or not as effectively, pre-compressed as the inner core), due to low or no real safety factor vs same it really doesn’t take much of a surge or overpressure condition to crack the coating and thereby quite jeopardize pipe (if it was not vulnerable before). I noticed that in the public report available from the Water Research Foundation at that at least a few dozen of the reported large diameter concrete pipe failures tabulated by these experts were apparently attributed to “surge” (with several times that number simply bursts and/or corrosion etc, with no more information supplied).
In any case, concrete pipe with thin/small pressure containing components (meaning higher strain, less reserve) may well be less robust than some other pipes from the standpoint of surge. This is effectively summed up in the paragraph on "How pccp fails" on page 86 as, "In other words, there is a cascading effect: overpressure > coating cracks > wires exposed to water > wires corrode and break > pressure is transferred to the cylinder > core cracks > cylinder is exposed to water > cylinder corrodes and fails." (I would only add that if coating is also exposed to air at any time, carbon dioxide can also enter coating cracks and carbonate the mortar that was intended to protect the wires/rods.)
[Given the brevity of the information provided in the OP, and while high velocities in general may be kind of hard to avoid at least at some point in the life cycle of all pipelines, I fear the only short but reasonably accurate answer to this question may be, “It depends” (and agree with bimr, and erstwhile tag line of LittleInch to effect that more info on these forums might beget better answers – might even add a corollary that brief, open ended inquiries or fishing expeditions might on the other hand beget fish stories or fishy answers!)]
- Thread starter
- #9
- Thread starter
- #10
thank you all really appreciate your replies,
as LittleInch said, yes my network may contain silt materiel as the project area is lies in desert country..i found one two references as below,
- Maksimovic, C. (ed.) 2001,” Urban Drainage in Specific Climates”, IHP-V Technical Documents in Hydrology, No.40, Vol. III, M. Nouh (ed.) “Urban Drainage in Arid & Semi-Arid Climates” UNESCO, Paris.
- Ontario, MOE 2008: Design Guidelines for Sewage Works. ISBN 978-1-4249-8438-1.
by which i come to conclusion that it is better to restrict the velocity in concrete pipes/channels below 5 m/s. Hope you all see these references and will advise.
as LittleInch said, yes my network may contain silt materiel as the project area is lies in desert country..i found one two references as below,
- Maksimovic, C. (ed.) 2001,” Urban Drainage in Specific Climates”, IHP-V Technical Documents in Hydrology, No.40, Vol. III, M. Nouh (ed.) “Urban Drainage in Arid & Semi-Arid Climates” UNESCO, Paris.
- Ontario, MOE 2008: Design Guidelines for Sewage Works. ISBN 978-1-4249-8438-1.
by which i come to conclusion that it is better to restrict the velocity in concrete pipes/channels below 5 m/s. Hope you all see these references and will advise.
- Status
Similar threads
- Locked
- Question
- Locked
- Question
- Question
- Locked
- Question