Loads on flanges 1

[dragonix]

Hi,

I have to dimension the bolts in a flanged joint.
The flange connects two pipe section and in the pipes flows a fluid.

My questions is:

-the axial load which tries to separate the pipe sections how can be evaluated?

Thanks in advance

 

[BigInch]

A reasonable estimate for force caused by internal pressure is simply the pressure x cross-sectional area.

If your pipe is 12.75 inch OD and 0.500 inch wall thickness; pressure is 100 psig, the separation force would be,

F tension lbs = pi * ((12.75"-2*0.500")^2)/4 * 100 lbs/in^2

You may have additional forces caused by other mechanical loads on the pipe.

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[dragonix]

I have this doubt:
If the pressure acts radially, how can it generate an axial force?
Only if the pipe is closed at one side (like a pressure vessel) an axial load can be generated by the pressure..or not?? This is my doubt!!

I thought that the separation force can be evaluated using the fluid velocity :

F = A*(L/D)*(V^2)*0.5

Where
A is given by Moody's diagram
V is the fluid velocity in the pipe
L is the pipe lenght
D is the internal diameter

Thank you!

 

[BigInch]

Axial tension stress from end cap pressure is P*D/(4*wt) tending to cause axial elongation of the pipe. Known as "end cap force, or stress".
Radial stress * Poisson's factor (usually around 0.3 for steel pipe) creates an axial stress component, tending to cause contraction of the pipe.

Net axial stress is therefore PD/4/wt - 0.3 * PD/2/wt
But the radial force component is different from forces tending to cause separation, since the stress resulting from the Poisson effect is caused from radial forces, so no counteracting force is created in the axial direction, as long as the pipe is not restrained in that axial direction.

As for end cap forces being present in a long pipe, as opposed to a closed pressure vessel, all pipe is essentially closed end at one time or another, but when its not, the integral over length of flowing frictional shear forces of the fluid against the walls also adds or subtracts from the end force stresses, to ensure that all axial loads are in balance at any point.



"I am sure it can be done. I've seen it on the internet." BigInch's favorite client.

"Being GREEN isn't easy." Kermit

http://www.youtube.com/watch?v=hpiIWMWWVco

http://virtualpipeline.spaces.live.com