Pipe support forces

[mae1133]

I'm working on a project where I need to provide forces from a piping system to a structural engineer to design the support system. Attached is an example of one of the supports being designed. The fluid being transported is water at 20 psi. The velocity of the water is 9 fps. I know this should be quite straight forward, but can someone show the methodology in calculating the dynamic forces that the supports will need to support? Thanks

 

[TLHS]

Is this a closed pressurized system with restrained joints? If it is, then there shouldn't be dynamic forces unless you've got a specific water hammer scenario. The pressures at the elbows balance out.

 

[TLHS]

If the above is the case, your lateral forces will depend on the piping system design and will either be friction from thermal or occasional loads if unrestrained, or calculated seismic, wind, or thermal expansion restraint forces if restrained

 

[mae1133]

There are two similar systems. One is a gravity system running between two open tanks, so basically the higher head of one tank causing the fluid flow to the other tank. The other is a pumped system running between two open tanks. I was assuming there could be a scenario in both cases where someone closed a valve on the pipeline causing a water hammer scenario. Thermal loads are accommodated for by expansion joints. Also, this is inside a building, so wind loads are not present.

 

[CarlB]

Loads will depend on how the pipe is supported, at these supports and adjacent supports/connections.
The greater forces are probably due to temperature change (between constructed and max/min experienced), assuming pipe is anchored somewhere.
There is also a load from unbalanced fluid pressure at a joint, this is a hydraulics 101 problem. As I recall, velocity is not a factor.

 

[BridgeSmith]

If you're looking for the lateral forces to be resisted, the discussion here may help, and if you care to register, it looks like the calculator will give you the answer directly.

 

[BridgeSmith]

Momentum dictates that, yes, there will be thrust wherever the flow changes directions, and the magnitude of the thrust is directly related to the velocity.

 

[TLHS]

This is a piping design issue, not a support load issue. The latter comes from the former. Someone needs to take responsibility for the piping and process design. Maybe that's you in a given case, or maybe it's someone else. Even if any of these forces you're talking about exist, whether they transfer to the supports will still depend on how the piping and its restraints are detailed.

Your possible dynamic effects will depend heavily on how quickly the valves open. Gradual change has very little dynamic effect. Hard open/close has significant effect. Unless they're emergency valves, the proper way to deal with this is to ensure the valve opening/closing speed isn't excessive. There are formulas that can provide you with valve operation time for a given configuration to avoid water hammer.

Also, are the expansion joints such that the piping is broken into individual segments? In that case you may need to restrain it against general operating pressures.

Basically, your supports will be dependent on the intent of your piping system design, and it takes an understanding of the general operation to nail that down.

 

[delagina]

This is not a structural question. This is a pipe stress engineer question. Should be basic for any pipe stress engineer to answer and model in Caesar software.

 

[mae1133]

Thanks guys....I will repost in the appropriate area.