piping fluid velocity 2

[gordonmech]

dear friends,
can anybody send me the recommended flow velocity used to size the piping for different fluid such as water, hs, ls, ms, gasoline,...
Thank you?]

 

[Artisi]

Google would be a good place to start.

 

[BigInch]

Unless you have some very significant reason to deviate, keep it between 1 and 4 m/s.

 

[athomas236]

try Crane 410

 

[adamuk]

Again, it depends.

Obviously higher velocities can mean that you use a smaller (and therefore cheaper) diameter pipe for the same tranfer rate.

However... high fluid velocities introduce turbulence and increase the pressure drop down the line (and you need a bigger pump and more power). Higher velocities can also increase the effects of fluid hammer when, for example, emergency shutdown valves operate.

I would consult a process engineer. It's one of those things that they could do pretty easily.

Adam Potter MEng CEng MIMechE

http://www.ax-ea.co.uk

 

[zdas04]

It is common for people to start a design with some magical velocity number in mind. I think that this is putting the cart way out in front of the horse. At the end of the day you are trying to optimize life-cycle costs. Smaller pipe (and higher velocities) are less expensive to purchase and install than larger pipe (and lower velocities), but those higher velocities require larger pumps and more power consumption. It is foolish not to look at both capital expense and ongoing operating and maintenance expense. I generally find that the small-pipe end of the continuum also has higher maintenance costs (pumps working harder wear faster, high velocities can scour the passivisation layer off the pipe and increase corrosion risk) that can easily eat up all the apparent savings in going to smaller pipe.

I really don't think that there is a one-number solution to this problem, and I would encourage you to take a life-cycle approach.

David

 

[BigInch]

Fact is that you have to start somewhere, even if you eventually do a full design and include a life cycle cost analysis. Might as well start with a velocity and a reasonable pipe diameter based on that velocity, rather than some maximum pressure and fuel or electricity cost. Most all liquid pipeline solutions fall within those velocity constraints anyway, so you can also be reasonably sure that you will find the optimized design somewhere in the initial cases you can develop from that velocity range. When power is very, very cheap, you will find the higher velocities more economical, when power is expensive, the lower velocities will be more economical, but you can't get too far away from your average flowrate + 3/2*[σ] in any case, otherwise with velocities lower than average you can't deliver enough volume even pumping 24/7, and with higher velocities, tanks costs get way too unreasonable very, very fast. That's the built-in reality check.

 

[MJCronin]

For a good reference on this particular subject, try the "Piping Handbook" by Nayaar.....under piping flow design.

Not only must you consider different velocities for different fluids, pump suction velocities are different than pump discharges; saturated steam is different than superheated....etc....etc

 

[racookpe1978]

what is an "hs, ls, ms" fluid? You're covering many different fluids and many different properties and safety factors there. Erosion, corrosion factors, life cycle material cost, initial purchase costs differ too much to offer a "one size fits all" premise.

 

[katmar]

Rules of thumb like using velocity ranges are useful when you do not have the full information. At the start of a project when you have only the fluid flow rate and little information on pipe length, elevation changes, pipe fittings etc and you have to come up with an initial estimate of the pipe size then these rules of thumb are all you can rely on.

As a complete guess, I would estimate that upwards of 80% of all pipe sizing jobs would result in reasonable answers if all you used was the rule of thumb. Experience is all about knowing when you cannot rely on the rule of thumb and you have to do a detailed calculation taking other factors into account.

One difficulty is that these velocity recommendations can appear to the inexperienced as being one single factor, but actually there are different velocity recommendations for economic pipe sizing, noise, erosion, safety, insulated piping and so on.

Sometimes you have to work backwards - i.e. after you have done the detailed calculation go back and check that the velocity does not exceed the recommendation for whatever parameters you are concerned about.

One of the most practical guides in this regard is Norsok Standard P-001

http://www.standard.no/PageFiles/1134/P-001e5.pdf

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[gordonmech]

Dear racookpe1978,
ls means low pressure steam
ms means medium pressure steam
hs means high pressure steam

 

[BigInch]

First rule is don't mix gas/vapor and liquid line rules of thumb.

 

[omereada1]

This is my piping rule of thumb for the past eighteen years, nortured vastly by experience.
A. Liquid lines should be sized for a velocity of (5+D/3) ft/s and a pressure drop of
2.0 psi/100 ft of pipe at pump discharge. That means for a 3" diameter pipe, the velocity should be at least 6 FPS at dp of 2 psi/100 ft.

At the pump suction, size for (1.3+D/6) ft/s and a pressure drop of 0.4 psi/100 ft of pipe
D above is pipe diameter in inches.

B. Steam or gas lines can be sized for 20D ft/s or 1200D FPM, for a 4" pipe that translates to 4800 FPM and pressure drops of 0.5 psi/100 ft of pipe

C. Limits on superheated, dry steam or gas line should be (200 ft/s or 12000 fpm) and a pressure drop of 0.5 psi/100 ft of pipe. Saturated steam lines should be limited to 37 m/s (120 ft/s or 7200 fpm) to avoid erosion.

D. For turbulent flow in commercial steel pipes, use the formula from Crane Tech Paper #410. Crane's formulas is for long pipelines where the length parameter L is in miles, and for high pressure gas transmission. For low pressure formulas, use Crocker pages 177 and 178, or NFPA 54.

For all the formulas on gas and liquid hydraulics refer to the Bible of Piping Systems: Piping Handbook by Crocker, pages 1 through 179, Weymouth, Panhandle A and B, Spitzglass, Fritzsche etc. For sizing low pressure gas pipes use NFPA 54, 6.4.1 or any of the IGT formulas. The acceptable dP is usually 0.5 in w.c. Some of the formulas involve friction factors and Reynold's number, use the Fritzsche friction factor from Crocker, or friction factor formulas listed in Crane TP 410.

Henri Onuigbo, P.E.