Erosional velocity and liquid velocity 1

[MESSADAA]

Hi
I'm designing an oil network with pipesim software( liquid single phase). to evaluate the velocity, which one will be considered for the design ? erosional velocity or liquid velocity ? and in which case do we use each one ?
thank you for sharing your experience on that.

 

[chemebabak]

MESSADAA,
I would consider both. That is, pumped liquids are generally designed for a range of 5-10 ft/s. Also, I would not design to exceed erosional velocity [v = c / sqrt(density) ]; where v is in ft/s and density in lb/ft3. The question is what is the value of c. Some fluids require 150 and others use 100, which is empirical. For either number the velocity would have to be much greater than 10 ft/s AND the density of the fluid would have to be much higher than water to exceed erosional velocity.

 

[zdas04]

Another way to say it is the errosional velocity is a "not to exceed" number.

The target design fluid velocity is economics. Any dP that is lost to friction is either energy that you didn't have to spend or energy you are going to have to add back in to finish transporting the liquid. The faster the fluid flows, the higher the dP due to friction.

David Simpson, PE
MuleShoe Engineering

Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat

 

[fedi12]

Please refer to API 14E for line sizing in generalll

 

[LittleInch]

Whilst 14E is a reasonable guide, please do not take the limits mentioned as your limits. The scope of 14E is for piping on offshore production platforms.

If you have clean fluid then you will normally find that frictional velocity is what you end up sizing for. Don't forget the impact of surge either - this will impact your velocity and line sizing. As zdas04 quite rightly says, use any limits as not exceed number.

Remember that each system is unique and what is the most economic for one system may not be the same as for yours. Shorter systems can withstand smaller pipe / higher velocities compared to much longer or complex systems.

I realise people like to work to defined limits, but in this case any such limits are quite flexible depending on your particular situation. That's why design engineers exist.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[moltenmetal]

Line sizing is always an economic optimization exercise, and that optimum varies considerably with circumstances. Erosion in clean gas and clean unsaturated liquid service piping is pretty much an imaginary problem at velocities which are at all economic, otherwise you'd be replacing control valve trims every couple of months!