Pipe support design when fluid direction is changing?

[farhadsh]

I have an underground piping system with design pressure of 120 bar and fluid is mining paste. I am to design pipe supports. My question is only applicable to thrust and momentum change forces. The thrust and momentum created through the 90 degree elbows (horizontal /vertical) are very significant around 27,000 kgf at horizontal/vertical plane. Assume I only want to control thrust and momentum forces created when fluid direction is changing:
Do I need to put a pipe support at each elbow to resist such thrust/momentum change ?
Or I should consider such forces are balanced out with other elbows depending on the piping layout and check what force is left and put a thrust support for it?

 

[LittleInch]

Well a lot depends on how the pie is supported, guided and restrained along the way.

This is why piping stress programs were invented and why piping stress engineers exist.

Try searching on this site for pipe stress analysis or looking up some basic piping design tools.

We can't tell anything from this description.

Maybe you'll need specific guides or restraints or anchors and maybe you won't.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[pennpiper]

farhadsh,
A little information might help:
- What size are these pipe lines?
- Is the piping butt welded or mechanical joint?
- What kind of Pump is it (Centrifugal or Positive Displacement)?
- By "Underground", which do you mean buried or in a tunnel?
- If the pipe is buried then how deep is it buried?
- What kind of soil is it, Stable well compacted soil or loose sandy soil?
- What else can you tell us?


Sometimes its possible to do all the right things and still get bad results

 

[farhadsh]

Maybe I can add more detail. Please note I am only interested to see if flow direction change in piping system has impact on pipe support design
We know pipe elbows change flow direction and there is formula to calculate force on elbow. linear momentum or whatever you call provide forces from fluid on elbow which has elements of thrust force PA and elements of Velocity change density*flow rate*speed. In case of 120 bar design pressure with 6 " pipe and 1.5 m/s fluid velocity the magnitude of such force on elbow will be very high close to 27,000 kgf. The thrust force element PA is majority of this force and element of density*flow rate*velocity can be ignored. Do I need to consider this force when design pipe support?
To design pipe support do we calculate such force on each individual elbow and then check if forces on all elbows are canceled out? Or this is totally wrong path and we only consider weight of pipe and fluids for design?
I did lots of search but did not find any link between support design and thrust forces
Thank you,

 

[farhadsh]

Here is info

- What size are these pipe lines? 6"
- Is the piping butt welded or mechanical joint? Victaulic coupling
- What kind of Pump is it (Centrifugal or Positive Displacement)? PD
- By "Underground", which do you mean buried or in a tunnel? Tunnel and piping hanging from tunnel ceiling
- If the pipe is buried then how deep is it buried? N/A
- What kind of soil is it, Stable well compacted soil or loose sandy soil? N/A
- What else can you tell us?

 

[bimr]

In general, because joints can be welded, steel pressure pipe usually does not require thrust blocks at special sections (valves, tees, elbows, reducers, etc.). For welded joints, the pipe itself provides thrust restraint. Welded joints are usually able to resist full thrust.

Welded Pipe

Please post a detailed description of your piping system so that it is possible to understand the scope of your project. Otherwise, the responses to your question will consist of educated guesses.

 

[racookpe1978]

Yes, ANY mechanical joint (Vitalic) clamped using rubber fittings and hand-tightened fittings seeing oscillating flow MUST be restrained against undue motion in all directions. This includes flow (water hammer) induced sudden forces if flow reverses or is suddenly stopped or started.

 

[farhadsh]

bimr, as far I know thrust block is used in buried system while my piping is hanging from wall. I guess assuming mechanical joints /welded joints can resist thrust still such force is transferred to pipe and pipe needs to be restrained to wall

 

[bimr]

bimr, as far I know thrust block is used in buried system

Most people have moved away from the used of thrust blocks for buried piping for numerous reasons. Thrust blocks have fallen out of favor because thrust block design is based on unknown characteristics of soils.

Thrust blocks were generally used on unrestrained connections (bell and spigot) for underground work. Most piping is now restrained in some manner using restraints such as megalugs.

Do I need to put a pipe support at each elbow to resist such thrust/momentum change?

Now that you have posted additional details.

The answer is no, not at every elbow. Flexibility is required for pipe design. The only time you would get a thrust reaction would be in a dynamic event if someone reversed the flow while the fluid is in motion. For that thrust, it is typical practice to install an anchor in the middle of the pipe straight run(s).

For references I suggest:

Piping Design-Kellogg
Piping Design and Engineering -Grinnell
Piping Handbook Mohinder Nayyar

Just noticed that you are proposing Victaulic type piping. The support design will be more difficult than for welded pipe. Perhaps you are using this piping system as temporary. See the victualic design manual for design examples.

Refer to example #6:


victaulic

 

[pennpiper]

farhadsh,
Where are you in the procurement of the mechanical joint piping material?
This question is very important.

The cost of Butt weld Carbon steel pipe may be a little more than Victaulic coupling pipe (when you consider the Welding and NDE) but this difference is bound to be more than offset by the cost of providing the proper anchors for mechanical joint piping.

Sorry but I am retired and no longer have access to the proper information necessary to answer this question.

How about you provide an isometric of the system (with dimensions) so someone here can estimate the cost of both methods?



Sometimes its possible to do all the right things and still get bad results

 

[farhadsh]

Pennpiper & bimr; Thank you for inputs I am at design stage of the job and Victaulic HP-70ES is selected for job. This coupling are suitable to handle 120 bar thrust force. Based on replies I got It looks if I put anchor near vertical elbows to restrain X-Z and on horizontal elbow on X-Y direction it should restrain thrust forces.

but disregard type of coupling used for piping system (grooved or welded ANSI flange) thrust and momentum force is created wherever there is a flow direction change in piping and I guess such force needs to be restrained by support. For instance if we design system with 100 bar vs 10 bar the thrust forces will be 10 times more and so supports need to be stronger? the design pressure has direct impact on support design.
any input is helpful

 

[GD2]

farhadsh,
For some reason, I am not sure if you are following a correct procedure. Usually, a stress analysis of the overhang piping system should be done for two cases - Forward and reverse flows. The analysis will determine the forces, moments, type of support required and then you go in to design the supports. If you find it intimidating, you can approach pipe support manufacturers who has tools and resources to design supports for you.

Ganga D. Deka, P. Eng
Canada

 

[farhadsh]

GD2: Could you give reasoning why analysis is needed for reverse flow?

 

[LittleInch]

I looked up the HP-70ES fittings. Just remember you need grooved pipe and fittings to make it work.

but yes - you need to include in your design some means of securing the piping either at supports or specific guides, anchors or pipe stops.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[GD2]

Farhadsh,
If there is no temp difference on the flows, you need not do stress in both directions.

Ganga D. Deka, P. Eng
Canada