Pipeline Velocity Calculations
Pipeline Velocity Calculations
(OP)
Hi, I am new to the forum so forgive me if i have put this thread in the wrong location.
I am looking for some help and advice on a calculation i have transposed in order to help size cooling lines on a diesl firewater pump package.
The calculation takes the pipe size in inches, and the pipe velocity limit in m/s and provides the maximum allowable flow in L/S (messed up i know but that's just the units i have to work with haha!)
Anyway, this is what i have got:
=((((2*0.0254)^2)*5)/1.274)*1000 2 = the pipe size 5 = the volocity limit.
(Apologies for the layout, i grabbed it out of my excel spreadsheet)
I originally started with the volocity calculation v=1.274q/d^2 and transposed to get to my formula, adding in sections to change units along the way.
Does my transposition look correct or is there something i am missing? I ask because we have a pipeline velocity slide rule from a supplier of ours and it appears to give quite different values to those that my calculation has provided:
pipe size my calc sliderule
1/2" 0.63 0.975
3/4" 1.42 1.7
1" 2.53 2.75
1 1/4" 3.96 4.8
1 1.2" 5.7 6.5
2" 10.13 10.8
2 1/2" 15.83 15.2
3" 22.79 23.5
4" 40.51 32.25
6" 91.15 91
8" 162.05 160
I accept that the values read off of the sliderule are not going to be absolutely accuraute but there is quite a considerable difference on some of the pipe sizes. (ie the difference betweenthe values for 1/2" equates to around 2.5 m/s on the slide rule)
Basically i am after a sanity check. Is my calculation correct, and the sliderule wrong; or is there a flaw in my calc somewhere?
Additionaly, a colleague has a comment on another formuala of mine for calculating pipe size, given velocity and flow rate. He has suggested that maybe i should consider temperature or density for my calculations. Will this have much of an effect on the velocity/pipe size/ flow rate, or is any efefct negligable.
If they do need to be included, could anybody suggest a transposition of the velocity formula to include for this?
Apologies for rambling on, i hope i've not been too hard to understand!
Thanks
I am looking for some help and advice on a calculation i have transposed in order to help size cooling lines on a diesl firewater pump package.
The calculation takes the pipe size in inches, and the pipe velocity limit in m/s and provides the maximum allowable flow in L/S (messed up i know but that's just the units i have to work with haha!)
Anyway, this is what i have got:
=((((2*0.0254)^2)*5)/1.274)*1000 2 = the pipe size 5 = the volocity limit.
(Apologies for the layout, i grabbed it out of my excel spreadsheet)
I originally started with the volocity calculation v=1.274q/d^2 and transposed to get to my formula, adding in sections to change units along the way.
Does my transposition look correct or is there something i am missing? I ask because we have a pipeline velocity slide rule from a supplier of ours and it appears to give quite different values to those that my calculation has provided:
pipe size my calc sliderule
1/2" 0.63 0.975
3/4" 1.42 1.7
1" 2.53 2.75
1 1/4" 3.96 4.8
1 1.2" 5.7 6.5
2" 10.13 10.8
2 1/2" 15.83 15.2
3" 22.79 23.5
4" 40.51 32.25
6" 91.15 91
8" 162.05 160
I accept that the values read off of the sliderule are not going to be absolutely accuraute but there is quite a considerable difference on some of the pipe sizes. (ie the difference betweenthe values for 1/2" equates to around 2.5 m/s on the slide rule)
Basically i am after a sanity check. Is my calculation correct, and the sliderule wrong; or is there a flaw in my calc somewhere?
Additionaly, a colleague has a comment on another formuala of mine for calculating pipe size, given velocity and flow rate. He has suggested that maybe i should consider temperature or density for my calculations. Will this have much of an effect on the velocity/pipe size/ flow rate, or is any efefct negligable.
If they do need to be included, could anybody suggest a transposition of the velocity formula to include for this?
Apologies for rambling on, i hope i've not been too hard to understand!
Thanks





RE: Pipeline Velocity Calculations
v = Q/A = units of m3/s/m2
A = pi()/4 * d^2 "d" is in meters, π is in ... π
v = 4/pi() * Q * d^2
If Q is in m3/s and d is meters, that's the end of it.
If Q is in l/s and d is meters, divide by 1000
No more math problems please. Math is some other website.
Independent events are seldomly independent.
RE: Pipeline Velocity Calculations
That being said, mixing English and metric units in the same calculations, without thorough explanation/depiction is admittedly at least confusing.
RE: Pipeline Velocity Calculations
Thanks for your reply, i think i understand where you're coming from.
However, i don't believe that my problem was a maths related one. I am 99% confident in the formula i used i just wanted clarifcation that i hadn't missed something important, such as density or temp considerations, as mentioned in the latter part of my post. I fail to see that a maths advisor would know much about the minutii of a fluid mechanics formula.
Many thanks
Jonathan
RE: Pipeline Velocity Calculations
RE: Pipeline Velocity Calculations
Your basic formula is v=Q/A. Even math guys get it.
Oh I see where you're coming from. Math guys never include the units.
Independent events are seldomly independent.
RE: Pipeline Velocity Calculations
Both my calculation and the slid rule work from the nominal diamter of the pipe in question, thus being the ID
I shall try converting all the various parts into one unit form beforehand ans then calulcating again to see if i still get the same differences.
Addittionaly, do you know iw any consideration of temperature or density is required when calculating the required pipe size from a given velocity limit and flow requirement?
Many thanks
Jonathan
RE: Pipeline Velocity Calculations
Basically, i wrote a calculator that takes a user specified flow requirement, and velocity limit will provide a pipe size required to meet such requirements. We use two materials of pipe, 316SS and 90/10 cu/ni, with maximum velocity limits of 5 and 3.6 m/s respectively, determind by the engineering powers that be here. my line manager asked me to include a box for max rate of flow in whichever pipe size, so that the user can see how far their required flow is from the maximum flow of the pipe size the claculator selected. A colleague then asked if i had taken into accound the temperature and density of the fluid being piped, as we pump fresh and sea water, direct from source. This is what led me to your good selves.
Thanks
Jonathan
PS didn't mean to sound ratty in my previous response BigInch!
RE: Pipeline Velocity Calculations
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: Pipeline Velocity Calculations
Independent events are seldomly independent.
RE: Pipeline Velocity Calculations
RE: Pipeline Velocity Calculations
That being said, in this age of e.g. ExCel spreadsheets I agree with cvg that there is little need for slide rules that were once very common (as long as we have electrical power, and that is not knocked out!), as the effective ID to determine velocity from flow is simply OD - 2(wall thickness) in the case of unlined pipes or OD - 2 (wall plus lining thickness) in the case of internally coated or lined pipes.
As for me and my house, I will at least keep some rules in the drawer.
RE: Pipeline Velocity Calculations
Thank you all for your replies, very helpful indeed!
RConner, that was my exact thinking in digitising this calculator, once written, its far easier to do it onexcel, with much less chance for user error. And i see what you mean, we may consider a 2" nb to be exactly 2", whereas the sliderule may consider it to be 2.05" for example.
BigInch, cvg, I'm very inclined to aggree wholeheartedly with you. The application is fire protection on O&G rigs so unless the disastrous happens, the system will only ever be run for 1 hour per week. As such, i think you're right that any effects of heat and desnity etc will be wholly negligible.
Many thanks
Jonathan
RE: Pipeline Velocity Calculations
2" od is actually 2.375"od,
4" is 4.5", 6, 6.5"
8, 8.625
10, 10.75
12, 12.75
14,14
As you are using stl, which is often quite thin, your ID is almost certainly bigger than the nominal size.
Especially at the low sizes, it will make a big difference but there is no excuse for getting it wrong.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Pipeline Velocity Calculations
Thats crystal clear now! I used the correct values for various schedules and now my figures are much more correlative with those of the sliderule. Time to banish it the back of the drawer!
Thanks guys!!