Force at Pipe Bends - Pipe Support
Force at Pipe Bends - Pipe Support
(OP)
Let me start by apologizing for my lack of knowledge in this area. I am not designing the lateral resisting system for the pipe in this case only the vertical forces. However my interests have been sparked. My questions are probably pretty academic.
A few questions:
Lets consider a 16" diameter pipe with a pressure of 40psi and the forces at a 90 degree bend.
First if you have the pressure and diameter and you neglect losses, you can determine the velocity and flow rate. Using V=sqrt(2*g*p/unitweight)
Next you apply a free body to the pipe bend a solve for the reactions.
I've attached a calculation that shows this and I'm wondering if this is correct. Seems like the forces are quite large (although 40 psi is pretty high I suppose). Maybe this is due to neglecting losses?
http://files.engineering.com/getfile.aspx?folder=f...
Any feedback is greatly appreciated. And I realize this is basically straight out of the text book but I'm wondering how this get applied in practice? Is it similiar, but need to account for losses and change in pipe size?
Thanks!
A few questions:
Lets consider a 16" diameter pipe with a pressure of 40psi and the forces at a 90 degree bend.
First if you have the pressure and diameter and you neglect losses, you can determine the velocity and flow rate. Using V=sqrt(2*g*p/unitweight)
Next you apply a free body to the pipe bend a solve for the reactions.
I've attached a calculation that shows this and I'm wondering if this is correct. Seems like the forces are quite large (although 40 psi is pretty high I suppose). Maybe this is due to neglecting losses?
http://files.engineering.com/getfile.aspx?folder=f...
Any feedback is greatly appreciated. And I realize this is basically straight out of the text book but I'm wondering how this get applied in practice? Is it similiar, but need to account for losses and change in pipe size?
Thanks!





RE: Force at Pipe Bends - Pipe Support
http://www.freestudy.co.uk/fluid%20mechanics/t7203...
RE: Force at Pipe Bends - Pipe Support
So I guess my questions are: in practice, do you guys normal derive the velocity using the pump output values then accounting for reductions? If you were to assume a velocity similar to what I had assumed in my calculation, this would be pretty conservative for finding forces at bends I suppose?
Thanks again!
EIT
www.HowToEngineer.com
RE: Force at Pipe Bends - Pipe Support
If you have a pressurized system you always have a change in momentum force and a pressure force. At first this seems like you're accounting for the pressure twice. Meaning that the velocity is is affected by the pressure and the force at the bend is affected by velocity, but then you also add in the pressure force again to account for the force of the pressure...
This was probably explained my fluid mechanics class at some point..
EIT
www.HowToEngineer.com
RE: Force at Pipe Bends - Pipe Support
http://www.engineersedge.com/fluid_flow/simplified...
Are you asking if there are forces at pipe bends that require some type of restraint?
The force from the moving fluid is constrained by the piping so there is no outward force at a pipe bend except for the weight of the pipe and fluid.
If you have a nozzle on an open end of the pipe, then you would be have to account for the fluid force.
In the case of unrestrained pipe such as bell and spigot piping, there is force at the pipe bend. This is usually dealt with by restraining the pipe adjacent to the pipe bend.
RE: Force at Pipe Bends - Pipe Support
without seeing the actual orientaton of what you're trying to do it's difficult to see whether some forces would act together or cancel each other out. If you have a vertical leg which exits to atmosphere, fair enough you have a force from the pressure, but if the vertical leg than truns horizontal again, that pressure force is nearly cancelled out by the upwards one on the next elbow. Results in axial stress in the pipe, but not the support.
What about weight of pipe and contents?
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Force at Pipe Bends - Pipe Support
The pressure is going to cancel out and is really a force on the pipe. So if you had a welded on or bolted elbow then there would be a force at this joint. However the force on an external restraint would be the force from a change in moment, right?
As for gravity loads, wind, EQ, temperature - that I can account for. It is the fluid mechanics portion that had me wondering.
Thanks again!
EIT
www.HowToEngineer.com
RE: Force at Pipe Bends - Pipe Support
As I said above - are you talking steady state (though 22mmsec is rather fast) or a wholly solid slug (normally doesn't exist) in what is usually an empty pipe?? In the latter case you need a whole lot of support with forces or the pipe literally jumps off your support and chaos follows.
If you give us the whole picture then we might be able to offer some advice....
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Force at Pipe Bends - Pipe Support
Not exactly sure what you mean by solid slug. Is that like opening the value fully open rapidly (I know there is a term for this....) or closing rapidly? I am referring to steady state I believe.
The whole picture -
Various size pipes carrying fluid for waste water treatment plant. Sizes range form 16" to 36" with flow rates ranging from 2000 gpm (gallons per minute) to 5,200 gpm. The pull fluid from tanks and transport to other tanks. Really our design is EQ and vertical force related. But I was also curious about the transfer of the momentum of the fluid flow at bends.
Is there other information that would be helpful?
EIT
www.HowToEngineer.com
RE: Force at Pipe Bends - Pipe Support
what you refer to in opening / closing rapidly is surge aka water hammer, which can result in sudden large forces on supports and piping and again can lift pipes off simple supports quite easily, not to mention overstress the pipe from internal pressure spikes.
Thinking up the transient events / things that happen at initial fill / refilling after drain down is key to your occasional loads. Holding down the pipework or providing restraints on movement to stop it jumping off your supports is usually a good idea...
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Force at Pipe Bends - Pipe Support
You only need to be concerned when you are working with unrestrained pipe (bell and spigot).
RE: Force at Pipe Bends - Pipe Support
http://www.uspipe.com/Files/200611141014260.DIPRA_...
http://www.american-usa.com/system/assets/141/orig...
RE: Force at Pipe Bends - Pipe Support
RE: Force at Pipe Bends - Pipe Support
RE: Force at Pipe Bends - Pipe Support
True, very, very few colleges would have ever done this training, but too few get it nowdays from anyone. Then again, perhaps too few realize that they need it.
RE: Force at Pipe Bends - Pipe Support
Thanks for all the help and the link by rconner was helpful similar problem and thanks for the further info CVG. I do see now that the momentum forces are pretty small for the velocities I'm dealing with.
EIT
www.HowToEngineer.com