Vertical pipe support load

[ttoonnyy]

Hi Guys

I got this question for a vertical pipe, hundreds meter deep for underground mine dewatering.
I'll need to work out the weight to support for the hanger design. No piping engineer to provide the load, unfortunately...
The total pipe weights about 5t and content weights 7t. vertically positioned, lateral controlled every 6 meter.
No expansion, dynamic, water hammer load considerd for now.
For the vertical load, there are 2 supporting options
Option 1
1 hanger hung the pipe from very top, the pump is connected at very bottom.
Therefore will generates a 12t weight for the hanger.
If this is the case, assuming the pipe is strong enough..can the pipe carry 7t content vertically?
Does the content pass whole gravity to the pipe wall through pressure and friction?
I see the reference from Peng engineering ASME mentioned the pipe line load should consider content as line load, not sure if it fits here.
Option 2
1 hanger hung from the very top, and another hanger/support from the very bottom before connecting to pump.
If this is the case, should bottom hanger undertake 60%+ of the total (pipe+content load); the top hanger undertake minimum 50% of the total (pipe+content load)?
Or bottom hanger undertake 7t content + 50% of the pipe load (5t)?


Would appreciated for any comments.
Cheers, Tony

 

[GBTorpenhow]

Need a sketch.

If open to the fluid at the bottom I have a hard time imagining how the weight of the contents could show up as tension in the pipe. Usually the weight of the contents appears as hydrostatic pressure only.

Production/injection well strings are typically supported only at the wellhead as I recall and hang freely into the well so yes, the entire weight of the pipe string can possibly be supported as tension at the top of the string assuming the pipe is strong/thick enough.

Bottom support might be tricky, any compression loads would be probably be undesirable as such a long string would have very low buckling resistance

 

[LittleInch]

It all goes on what is happening at the base of the pipe and the flexibility of the connection to the pump.

I would normally have thought that the end cap force from the weight of the fluid in the pipe would be taken by base support with some sort of fixed support, but maybe not.

contents will not cause a force on the pipe from friction and pressure, but end cap force will have an impact if the pipe is free to move at the base of the shaft.

If you have two supports then it all starts to get a bit complex depending on the level of either thermal expansion between installed condition and operating or strain expansion of the pipe.

In theory the top hanger could then be a spring hanger sized for the weight of the pipe, with a vertical force of 5 tonnes, with the base support being responsible for the fluid weight. But any failure of the top hanger or too much expansion or contraction of the pipe outside the range of the spring hanger could leave the base support supporting it all.

 

[Snickster]

Option 1

The weight of the contents will be transferred to the pipe at the bottom elbow pushing down vertically, plus weight of pipe will be total design weight for the hanger. I don't see any issue with letting pipe hang from a single hanger above with lateral bracing along the pipe as you mentioned. The pipe will stretch downward due to weight of pipe and contents equal to e=S/E where e is % strain. Also there may be some thermal expansion and with one hanger at top of pipe all thermal expansion will be forced downward. Therefore pump nozzle piping needs to be flexible enough to absorb this deflection without overload of pump nozzle. This will be the tricky part.

Option 2

I believe if the bottom support were perfectly rigid then it would feel the entire weight of content load. This is because the only way the top support can feel any load applied at the bottom elbow is due to the pipe stretching in accordance with the equation shown above. If the bottom support is so rigid it does not move at all then the vertical pipe cannot stretch and therefore no load can be felt by the upper support. The bottom support will likely not be absolutely rigid and deflect somewhat under load which will allow the pipe to stretch and transfer some load to the top support depending on the relative stiffnesses of the upper and lower supports. In this case the weight of the pipe will be shared by both the upper and lower supports based on the relative stiffnesses of the supports.

If it were me, I would just design the upper and lower supports for the entire load. 24,000 pounds is not that significant for a pipe support that will make it much larger in size relative to say if you designed it for only 12,000 pounds on each support. It will allow the flexibility to remove say the bottom support if required to service the pump if required.

If there is thermal expansion the upper support will likely need to be a spring support since any thermal expansion should be directed upward away from the pump nozzle with a rigid support at the lower end. In this case although both supports will be designed for full weight plus content load, the upper spring can support will be sized based on the expected actual load it will carry at the deflection expected for determining spring sizing requirements, whereas the structural support that the spring support attaches to should be designed for the total weight of pipe and contents.

 

[goutam_freelance]

For option 1, there should be an expansion joint at the pump discharge, as the thermal expansion for the atmospheric temperature range(about 50 deg C) may be close to 35 mm. It will be difficult to provide piping loops inside mines to absorb this amount of expansion, considering it is possibly a 10" pipe.

 

[ttoonnyy]

Thanks gents. I really appreciated your help!!!

I designed as total for conservative. I'm still holding a concern that the bottom part of pipe will buckle if they put a dummy support at the very bottom.

A flexi connection at the bottom would be best, as well as string lifting from the top. The pipe is not directly connects to pump, but through another horizontal pipe. Not opened.
I guess this horizontal pipe can provide enough deflection for the vertical movement? Meanwhile, the pipe is under tension from the top, there might not be further expansion if the content temp remains the same?

Just trying to figure out how does the vertical pipe undertake content load in the beginning, because both AI and books i read tells to assume pipe load as line load. I recon that may comes from the pipe stress modelling purpose?

For Option 1
If consider the bottom bend/elbow undertaking the whole content load, then pass it back to pipe wall, the bottom connection will be pushed to limit first, then the load will be passed back to pipe wall in vertical.
I did see the fire water pipe hanging all the way down to botton fire pump in other projects, 45 degree bend, the pump flange is not damaged/leaked, the vertical distance would be something about 10 m. Maybe the pump is undertaking partial vertical load. I don't know how to explain that to the client at that time. The 100DN pipe/flange shouldn't be taking that load....
For Option 2
If the bottom bend undertake the whole content load then pass over, the bottom support will be loaded with full content load + portion of the pipe load. Because the force always goes to shortest path, it won't pass back to pipe wall if the bottom support is rigid enough imo. Guess the bend are nomaly designed with a much higher load factor than the straight pipe.

Thanks again!!!!

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[Snickster]

I designed as total for conservative. I'm still holding a concern that the bottom part of pipe will buckle if they put a dummy support at the very bottom.

I never designed such a long vertical drop before so I would be very conservative. I don't know how long but you may be talking about 1000 feet? I would not use a dummy leg at the bottom elbow with so much load bearing down on it, the supported pipe will likely be overstressed or the connection weld may crack. If I used multiple supports I would probably support at bottom, center and top on spring supports that would allow for thermal expansion and such that any two supports could support the entire load. If you are just supporting at the top I would use two supports with one redundant where any one could support entire load. Then you would have lateral supports as you previously indicated along the length.

A flexi connection at the bottom would be best, as well as string lifting from the top. The pipe is not directly connects to pump, but through another horizontal pipe. Not opened.

A flex connection would be good to absorb any pipe movement downward.

I guess this horizontal pipe can provide enough deflection for the vertical movement? Meanwhile, the pipe is under tension from the top, there might not be further expansion if the content temp remains the same?

The pipe will stretch due to the weight of metal and contents. If it is supported at top only it would stretch down and could be on the order of inches depending on the stress in the pipe per equation e=S/E.

Just trying to figure out how does the vertical pipe undertake content load in the beginning, because both AI and books i read tells to assume pipe load as line load. I recon that may comes from the pipe stress modelling purpose?

I think as far as a computer program looks at it, it is a line load where weight of contents and pipe is considered to act along the pipe. However I believe the weight of the contents acts on the bottom elbow for a long vertical suspended pipe. The pressure due to the static height of the fluid at the bottom elbow is the weight of the fluid divided by the area of the pipe. This only acts on the bottom elbow and not on any of the piping above. Therefore If you install a theoretically absolute rigid pipe support at the bottom then it will feel the entire load of the contents, if the other supports above are less rigid. Otherwise the load will be shared based on the relative flexibility of each support. So to insure all supports share equal load you would make them all of equal flexibility.

For Option 1
If consider the bottom bend/elbow undertaking the whole content load, then pass it back to pipe wall, the bottom connection will be pushed to limit first, then the load will be passed back to pipe wall in vertical.

If you put a rigid dummy leg support at bottom under elbow and it is rigid compared to any other supports which are may be relatively flexible, then it will take the most of the content plus pipe weight load until it deflects. The only way a dummy leg support is going to deflect is if the concrete foundation it is on settles. Only then will the load be shared by the higher more flexible supports.

I did see the fire water pipe hanging all the way down to botton fire pump in other projects, 45 degree bend, the pump flange is not damaged/leaked, the vertical distance would be something about 10 m. Maybe the pump is undertaking partial vertical load. I don't know how to explain that to the client at that time. The 100DN pipe/flange shouldn't be taking that load....

With only 10 meter hanging and rigid support at the top without any thermal expansion, the load is supported by the support at top without any load on pump nozzle. However if that was a 1000 foot long vertical drop you then have to consider the stretching of the pipe down in accordance with e=S/E which could be on the order of inches. Then the pump nozzle will be loaded.

For Option 2
If the bottom bend undertake the whole content load then pass over, the bottom support will be loaded with full content load + portion of the pipe load. Because the force always goes to shortest path, it won't pass back to pipe wall if the bottom support is rigid enough imo. Guess the bend are normaly designed with a much higher load factor than the straight pipe.

The bottom support if a rigid dummy leg will take most of the load period, if the other higher supports are more flexible. That is why I would not put a dummy leg at bottom but put same supports of equal flexibility along the vertical length of pipe to insure they share equal load. Bend are actually less strong under deflection generated stress than straight pipe due to stress intensification factor SIF, but has same strength as straight pipe under pressure stress.