Pipe Design
Pipe Design
(OP)
Good Morning,
I have read about the considerations for the design of pipe lines and usually, there are two parameters for the selection of the diameter:
1.velocity
2.Pressure drop
My question is which one must be the main factor to take into account for the final selection?
I mean, the pressure drop has an influence on the discharge pressure of the pumps and a higher velocity might originate vibration and erosion. But, if I have a system in which both parameters -velocity and pressure drop- are in acceptable values, how can I improve my design?
Should I increase the velocity or reduce the pressure drop?
bye
I have read about the considerations for the design of pipe lines and usually, there are two parameters for the selection of the diameter:
1.velocity
2.Pressure drop
My question is which one must be the main factor to take into account for the final selection?
I mean, the pressure drop has an influence on the discharge pressure of the pumps and a higher velocity might originate vibration and erosion. But, if I have a system in which both parameters -velocity and pressure drop- are in acceptable values, how can I improve my design?
Should I increase the velocity or reduce the pressure drop?
bye





RE: Pipe Design
Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com
RE: Pipe Design
RE: Pipe Design
I tend to design piplines with velocity between 10-100 ft/sec to control noise, scouring of passivation layers, and pressure drop. Then I look at how much hp is required to restore the pressure lost in friction.
David
RE: Pipe Design
RE: Pipe Design
Only exception is corrosion/erosion considerations, which is usually a velocity criteria.
RE: Pipe Design
I have been reading about "economic piping design" and I think -please correct me if I am wrong- this is related mainly with the pumping costs and the installation & maintenance costs. The idea is to find the diameter with the less total costs.
I usually designed with pressure drop (psi/ft), but now I agree with katmar -the "economic" pipe selection- because you could have an acceptable pressure drop but very high costs associated with the I&M.
Obviously, the process may add other factors for the selection (e.g, maximum velocity inside an instrument) and all selected diameters have to take this into account.
RE: Pipe Design
Because of the step change in the pipe size there is a step change in the economics and it is not a nice smooth curve that can be optimized using classical calculus. Experience has resulted in various "rules of thumb" that are good enough for you to get close to the optimum economics by sticking to the typical pressure drops. Similarly, experience has shown how far you can go with velocity before things like erosion, noise and water hammer become problematic.
It is really only with very long pipelines that you would put an effort into economic optimization. But how long is long?
Also, most of the literature assumes that you have a constant flow rate for the assumed 20 year lifespan of the pipeline. You will be lucky if things stay constant for 20 months. So we tend to design with a little bit of "safety margin" built in.
Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com
RE: Pipe Design
I believe this could be an improvement on the "selection" but it is still a short method to apply (e.g using a spreadsheet), especially when your process has for example 500 lines.
Mr Katmar, would you please tell me something more about the "rules of thumb" used in these cases.
Thank you,
Lijantropo
RE: Pipe Design
Another client has a max dP/mile of 5 psi for dehydrated lines and 15 psi/mile for wet-gas lines.
I've never seen any industry-wide rules of thumb.
David Simpson, PE
MuleShoe Engineering
www.muleshoe-eng.com
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
Remember, being ignorant isn't your fault; staying ignorant is.
RE: Pipe Design
I agree with David - the more universal the rule of thumb, the less likely it is to be helpful in your specific application. Check with colleagues in your particular industry for what standards they use.
Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com
RE: Pipe Design
Lij.
RE: Pipe Design
Pump discharge (liq or two phase) = 1 psi/100 ft
Pump suction (liq) = 0.2 psi/100 ft
Gases (P>15psia) = 0.3-1 psi/100 ft depending on pres.
Free draining = 1 ft/s.
Despite their simplicity, these rules cover a multitude of cases.
RE: Pipe Design
RE: Pipe Design
Mark Hutton
RE: Pipe Design
e.g. if we are pumping water with sand, it isn't good idea to flow with very high velocity, because it might corrode the pipe (and very fast), but, we don't want it to flow to slow, because sand can settle and clog the pipe.
Also, there is a rule I like to follow. The pressure lost by velocity should be around 15% to 20% of TDH.
So, if pressure lost by velocity is higher than 20%, you must consider to low the velocity. This saves money during operation.
If pressur lost by velocity is less than 15%, you may consider to use a smaller pipe diameter. This will save you money during installation.
RE: Pipe Design
In short, we can said that pipe sizing depends on overall costs. However, it must be taken into account design parameters related with material handled or process requirements.
Regards,
Lij