Best Diameter of Pipe 2

[scottbuckner]

I am wondering what the best diameter of pipe is for a given volume flow rate. I understand that conductors are sized based on flow velocity, surface roughness etc. but I have read that fluid friction is reduced at the point of transition from laminar to turbulent...Is there a critical velocity for each given pipe size? Thanks in advance.

 

[scottbuckner]

Also, if you look at a Moody diagram you'll see that Moody friction factor decreases with an increase in Reynolds number. How does this all relate to design and pressure drop?

 

[butelja]

The best pipe diameter is one that minimizes the life cycle cost of the system. The installation cost and operating costs are considered using time value of money concepts. Since there is a tradeoff between large pipes (high initial cost, low pumping cost) and small pipes (low initial cost, high pumping cost) there exists an optimum diameter.

If you are looking for "rule of thumb" information as a starting point, consider 5-8 ft/s velocity as a first pass to start an itterative analysis of varying pipes sizes.

 

i agree with butelja. LCC is the factor that will govern the optimum size of the pipe. F. C Yung has written an article " calc. optimum pipe size for vapor" that appeared in May 1994 issue of Hydrocarbon Processing (HP)mag. Previously, F.C. has written "Optimum size of pipe for liquids" that appeared in June 1993 issue of HP.

Another article prepared by Barry Sloane titled " Economic Pipe Size - based on payback" has appeared in July 1994 issue of HP. The HP has a website.

a couple of article related to pipe sizing can also be found in chem. engineering web site. u may also wnat ot try pipingdesign.com.

 

[kstaylor]

Several years ago there was a book written on this very subject, I have a copy. The info is as follows: Optimum Pipe Size Selection, by Claude B. Nolte, Trans Tech Publications, Clausthal, Germany, 1978.

The chapter titles are as follows: 1. Fundamentals of optimum pipe size selection, 2. Least annual cost, 3. Selection according to pressure drop available, 4. Velocity allowable, 5. Two-phase flow, 6. Fluid mechanics parameters, 7. Preparations, 8. Pipe size selection for pump or compressor discharge, 9. Pipe size selection for pump or compressor suctions, 10. Pipe size selection for pressure drop allowable, 11. Steam piping for heating and reciprocating pumps, 12. Steam piping for turbines, 13. pressure let-down for gas, 14. Relief valve discharge headers, 15. Steam trap piping, 16. Two-phase flow applications, 17. Special velocity considerations, 18. Comparative capacities of pipes, 19. Mechods of approach, 20. Conclusion.

The book contains numerous examples of all types of piping applications, one to fit almost any circumstance. I highly recommend it!

 

[Chanda]

As a thumb-rule, vapor velocities are limited to 30 m/s and keeping the dP less than 0.113 bar/ 100 m.
Also, liquid velocities are limited to 3 m/s but to 1.5 m/s for corrosive services.
The above are general guidelines and should be evaluated for the case considered.
For 2-phase flows, erosion velocity criterion needs to be checked (refer API 14E).
However, for 2-phase flow, nobody clearly mentions about phase velocities to be limited apart from erosion criteria. Logically, it should be checked. If anyone has something on this, let me know (especially kstaylor may have something in the book mentioned).

 

[inControl]

Dear all,

Here's some good software to help you:

http://www.pressure-drop-calculator.com/

(freeware)

or, even better:

http://www.pipeflow.co.uk/

(30-day trial)

I would size the pipe for a liquid flow around 1.5 m/s

Good luck & Happy New Year!

 

[davidribeiro]

As a matter of curiosity, is there anyone who has written a spreadsheet on calculating the Optimum Economic Pipe Diameter? I would greatly appreciate a copy thereof if so.

Regards
David Ribeiro
davidr@absamail.co.za

 

[sdprocess]

Hi davidribeiro,

I have a spreadsheet which calculates optimum economic pipe dia.Its not written by me though.If you are interested,give me your e-mail id. I will send it to you.

regards,
sdprocess

 

[davidribeiro]

Hi SDProcess,

Thank you very much, I think you have saved me a lot of time by your spreadsheet.

If I wanted to change the spreadsheet to suit my country's costs, does anyone have an idea on how to go about this? (South Africa)

Regards,

David Ribeiro
davidr@absamail.co.za

 

[Hookem]

Its simple folks: for single phase liquid flow (non-viscous, non-abrasive, etc.) use 7 to 10 feet per second (minimum of 3, maximum of 15). for single phase gas flow, use 45 to 100 feet per second; but only after first checking pressure drop (use .25 to .50 psi/100 feet). Then, depending upon future expansion, short term peaking, available space, equipment nozzles, etc. choose a diameter that is one larger or smaller.

If you are calculating life-cycle cost effectiveness, you have too much time on your hands.

 

[CRG]

Hookem

Time spent on life-cycle cost should be directly proportional to the scale of the project. If you are designing a 100' line, it does not justify the expense. However, if you are designing a 1000 mile pipeline, life-cycle cost are important and should be part of the design process.

 

[davidribeiro]

I think I will have to create a simplistic spreadsheet for my company's purposes. I wont go into lofe-cycle cost, but unfortunately can't find any literature on OEPD. Does anyone here have a *.pdf file on the subject that they can e-mail me.


Much appreciated

David Ribeiro
davidr@absamail.co.za

 

[CARF]

http://www.pressure-drop-calculator.com/

has been changed too:

www.carf-engineering.com

it is still freeware, please download the Economic Pipe Sizer under DOWNLOADS.

Hope this helps,
MVD

 

[davidribeiro]

Hi MVD

Thanks for the web site!

David