Mine shaft piping stress analysis
Mine shaft piping stress analysis
(OP)
The consulting firm I work for acquired a contract for the reconstruction of an underground mine pumping station. Because we are a small company we asked for the help of a piping stress analysis specialist. Although I don't know the subject so well so as to judge his work, I have some questions that I'd like to share.
- The specialist proposed anchors every 6m for the shaft's pipeline. As far as I know anchors should be placed in elbows, valves etc and not in straight pipelines. If anchors must be placed in straight lines then expansion joints are needed. When I asked him this question he said that due to the nature of the project (maintenance difficulties), any other type of support wouldn't work for the mine workers and that the only result will be a minor oversizing of the supports.
-I tried to check his results only for the shaft's entrance bend with this type http://www.engineeringtoolbox.com/forces-pipe-bend... but the number's were totally different. I imagine that is the result from the placement of the anchors. As far as I know stress analysis is checked between anchors so the resulting forces from the pipeline's weight are not calculated. The other thing that seems rather strange is that when I asked him to change the operating pressure, the resulting forces at the sustained load case didn't change that much. Probably I'm missing something fundamental here.
-Last question pipe shoes are modelled as anchors at softwares or as an other type of support.
Thank you in advance.
- The specialist proposed anchors every 6m for the shaft's pipeline. As far as I know anchors should be placed in elbows, valves etc and not in straight pipelines. If anchors must be placed in straight lines then expansion joints are needed. When I asked him this question he said that due to the nature of the project (maintenance difficulties), any other type of support wouldn't work for the mine workers and that the only result will be a minor oversizing of the supports.
-I tried to check his results only for the shaft's entrance bend with this type http://www.engineeringtoolbox.com/forces-pipe-bend... but the number's were totally different. I imagine that is the result from the placement of the anchors. As far as I know stress analysis is checked between anchors so the resulting forces from the pipeline's weight are not calculated. The other thing that seems rather strange is that when I asked him to change the operating pressure, the resulting forces at the sustained load case didn't change that much. Probably I'm missing something fundamental here.
-Last question pipe shoes are modelled as anchors at softwares or as an other type of support.
Thank you in advance.





RE: Mine shaft piping stress analysis
RE: Mine shaft piping stress analysis
RE: Mine shaft piping stress analysis
RE: Mine shaft piping stress analysis
RE: Mine shaft piping stress analysis
Thanks for your help!!
RE: Mine shaft piping stress analysis
The problem we have is that we have about 5% of the information to comment properly. So far we don't know
Size of the pipe
Pipe material
Pressure rating
wall thickness
orientation (horizontal / vertical/ angled)
length
temperature normal / running
pipe connection (welded / jointed / push fit
orientation of pipe (isometric)
Design code of pipe
External loads
I could go on, but I think you get the drift.
Full x,y,z,rx,ry, rz anchors every 6m sounds quite odd to me, but maybe it just made the analysis easy?
If you anchor things then you can get high stresses if you don't allow some movement, but it all depends - the pipe may be able to withstand it espevcially if it's thick and the temperature change is low.
also some aspects of your post are really quite puzzling without all the info you have e.g. "any other type of support wouldn't work for the mine workers" Eh?
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Also: There's usually a good reason why everyone does it that way
RE: Mine shaft piping stress analysis
Size of the pipe : 12"
Pipe material : ASTM A-106 B
Pipe Pressure rating : Sch80
Max pressure: 65 bar
wall thickness : 17,48mm
orientation : vertical
length : 350m
delta T : 5 °C
pipe connection : flanged
orientation of pipe : pump,bend,horizontal 50m,bend,vertical 350m,bend,horizontal 20m,discharge tank
Design code of pipe : ASME B31.1
No external loads
RE: Mine shaft piping stress analysis
A single support at the top with a 350m length hanging off it would seem to be stretching things (literally), but a full anchor support every 6m would also seem to be excessive. However, it will reduce the size of the support as the vertical pipe load will be shared amongst many others and any support failure would not be catastrophic. It's the full anchor bit that surprises me - I would have thought vertical supports every 15 to 25m and horizontal guides would have been enough, but maybe the difference is not worth bothering about and makes the vertical support too big.
there is a practical aspect also - as you say this is flanged I can only assume that you're planning on building this pipe in sections so multiple supports would be safer and easier to support. Getting a multiple flanged pipe in a dead straight line is wholly dependant on how accurate you weld the flange on. It's difficult to make up any angular misalignment on a flange
Also how do you attach the support to the concrete shaft? do you have space limitations?
did you design this pipe and then ask the stress man to "stress it" or did the specialist also design the pipework?
I can't see any big issue in having full anchors in terms of stress given the low temperature variation and really quite thick pipe, so maybe the specialist did this as a worst case run, it turned out OK so he stopped doing any other runs?
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Mine shaft piping stress analysis
You write..."I would have thought vertical supports every 15 to 25m and horizontal guides would have been enough, but maybe the difference is not worth bothering about and makes the vertical support too big.".
This is what I was trying to ask but probably I wasn't that clear when I wrote "any other type of support wouldn't work for the mine workers". I was thinking something like your proposal (anchors+guides) but he said to me that guides need maintenance and that is something that the maintenance department doesn't want.
As I can understand you think that the piping is oversized.
Finally the support to the concrete shaft is assigned to a structural engineer so I can't say really much.
Thanks again for your valuable help.
RE: Mine shaft piping stress analysis
I have no idea about the piping, but full anchors every 6m looks excessive.
However, the devil is in the detail which you and the stress man have and I don't so it's difficult to be any more positive than that.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Mine shaft piping stress analysis
Let me share a thought with you..
Because as I have said already the shaft is existing and we don't know its strength, full anchors every 6m will reduce the size of the support thus making its attachment to the concrete easier.
How does that sounds ?
RE: Mine shaft piping stress analysis
Anchors every six metres, if you have any dT at all, probably hurts the system more than it helps, at least until enough of them break that you end up with the number you should have had in the first place.
RE: Mine shaft piping stress analysis
RE: Mine shaft piping stress analysis
If this is'nt adequate for you, go find an experienced shaft miner.... he doesnt need to be an engineer but he will set you straight. You have admitted to being inexperienced so this is not meant to be a major criticsm , more you are gettingg advice from the wrong people.
RE: Mine shaft piping stress analysis
RE: Mine shaft piping stress analysis
No problem in getting info from those who have seen the realty of life in those particular situations. I gathered it was vertical eventually, but I suppose w all have different practical aspects to deal with. I probably wouldn't have designed it to be made up of 100 or so flanged joints, but then I can't figure out why you would needs to replace sections after a few years either. As said less anchors mean bigger single ones and that may not be practical.
It might sound stupid, but do you not get access down a shaft by a wire and basket type things?
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Mine shaft piping stress analysis
FL/AE = &L(T2-T1); I get F = {insert your number} kN and an axial compressive stress between anchors (due only to the dT) of {insert your own number} MPa. Are they "Ideal Anchors", or how stiff are the anchors, and what is the stress analyst planning as mitigative measures against what I perceive might be somewhat high loads generated between them?
I'll check my own numbers again, but this is why I am asking the question.
Sadly, my experience in these fora over the years has conditioned me to not offer any calculation results, because in the event an error might be found, the numerous nay-saying "error vultures" will latch onto it and the ensuing thirty posts will degrade into attacks on the competence of the individual trying to offer help.
It actually doesn't matter if its piping in a mine shaft or anywhere else. Can the concrete (and, *especially the concrete*) accommodate the loads?
RE: Mine shaft piping stress analysis
Maybe I'm a very poor engineer but I'm close to the end of my career and its way too late for me to even ask " what does Rx, Ry and Rz mean?? Similarily Fl and AE?? Perhaps that tells you how little structural engineering I've performed over the last 40 years but I'm pretty good with explosives, both theory and practical usage, and I do have some other knowledge which is perhaps almost unique to the underground environment so hopefully you'll cut me a bit of slack on the theory.
I would think that the inserts I would expect to find would take 0.75 inch bolts , possibly 1.0 inch. The brackets might be dedicated to a single pipe column but I would not be surprised to see "multi pipe brackets " which would hold the 12 inch pump line plus perhaps a 8 or 10 inch compressed air line plus a 4or6 inch water intake line and maybe a couple of 4160 or 13.8 kv electric feeders as well. Each shaft is unique but you should be getting the idea by now. And the concrete is nearly always sulphate resistant but perhaps what I would regard as normal deteroriation , you guys would regard as being horrendous. Its all a bit subjective I suppose.
RE: Mine shaft piping stress analysis
The OP asked if pipe anchors spaced 6 metres apart is a design that ought be be questioned. Pipe anchors, when specified by a piping stress specialist, have a very specific definition with very specific implications. In this very particular instance, my very rough calculations for the anchor force developed between ideal anchors by 12" SCH 80 A106B pipe came to 205 kN (46000 lbf) and a compressive stress of 12 MPa in the pipe. The pipe is fine, but the theoretical anchor force is high. My questions are centered around trying to establish what other assumptions or measures the stress analyst has taken that would suggest that the loads are really much lower than that and that, therefore, the "anchors" are fine.
RE: Mine shaft piping stress analysis
I have utmost respect for those who chooses willingly to travel to the bowels of the earth to extract things for the rest of us and as it gradually becomes clearer what and where this is used, the design becomes easier to understand and as said, the devil is in the detail. In those locations the desire is for something strong and easy to fix / replace, so doesn't lend itself to detailed design in the same way as several kms of piping / pipeline might. You also don't get solar gain down there in the depths....
Whilst this pipe is a bit longer, this type of design is fairly common on risers and shafts used for oil and gas lines, but we probably finesse it a bit more and it doesn't tend to have cages whistling up and down in close proximity many times a day.
Rx etc refers to rotation about axes. The anchor refered to doesn't allow any movement or rotation.
In reality it will probably be under axial stress due to hoop stress and poisons ratio as 5 C delta T is really small.
I still think you could use longer pipes and space the supports out more, but the design is acceptable, just could be chaeaper that's all.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Mine shaft piping stress analysis
As I can understand, you all agree (more or less) that the design is at least acceptable.
Miningman, I would like to give you a better picture for the installation in order to gain as much as I can of your experience.
The shaft was built somewhere in the early 80s and its diameter is 4,3m. Inside you can find the infrastructure that you described (cables, pipes etc.). Now our goal will be, to install the 12" pipe somewhere there.
This means that we need to drill some new holes and of course that SNORGY's question is very good..." Can the concrete (and, *especially the concrete*) accommodate the loads?". Now regarding the installation difficulties to be honest I can't say really much...because as I understand you are the only who was already a pretty good picture.
RE: Mine shaft piping stress analysis
RE: Mine shaft piping stress analysis
RE: Mine shaft piping stress analysis
Anchors in stress programs don't move regardless if you apply 1 tonne or 1000 tonnes of force so that took me by surprise - what is the max stress?
Those loads look very high for a 12" pipe support (1.5 to 10 tonnes force?) but is what happens when you "anchor" a straight piece of pipe and then add pressure or temperature difference
To be honest, without seeing all the details it's a little difficult to go much further, but perhaps if you post a "typical" support with loads, stress, deflection etc we might be able to see where this is going
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Mine shaft piping stress analysis
I have no idea how the analyst has come up with 15 kN as the computed reaction force between two anchors of full (X, Y, Z, Rx, Ry, Rz) restraints with dT = 5 C for 12" A106B pipe, but it sure is a different result than I get no matter what textbook I use (LC Peng's work among them) or CAESAR II model (yes, I did run it) I create. They are other nchors, or they aren't. I have no clue. But what I WILL say is, if the computed load of 15 kN is accurate, my concerns disappear.
RE: Mine shaft piping stress analysis
Let me share with you the results that I have in my hands. I will use the same terminology as it is described in the report that I have.
For the straight pipeline the computed force at an anchor node e.g 156 is, 590 kN (dT=10°C I have correct it that, at an earlier post),the load on restraint at the same node is 15 kN, the displacements are all 0.
At the two bends of the piping network (entering and exiting the shaft) the resulting force is around 750kN, the load on restraints is 700kN, the displacement is 0,17mm at the flanged joint of the bend and the straight pipeline.
The max stress intensity is 76083 kpA @ the exiting bend.
Is a modelling error possible? I mean maybe the bends, the straight pipeline should be checked separately. As I'm trying to read as much as I can these days, I see that eveyone is checking loads stresses etc. between anchors. Forgive me if I'm missing the fundamentals here but I'm starting to doubt about the specialist's abilities.
I can't understand how the anchor node resulting force is different than the load on restraint at the same node.
Maybe I didn't give him the right info?
Your thoughts...
RE: Mine shaft piping stress analysis
RE: Mine shaft piping stress analysis
What I think is being shown here is that the pipe is under a fairly high axial load resulting in axial stress. However apart from the bottom and top support, the rest are effectively fairly lightly loaded as all the pipe force from poissons effect / thermal expansion is being balanced by a similar force from the next pipe up the shaft - the 15kN. This force on the restraint is just for keeping it inline and allowing for the weight of the pipe between each anchor
However the last support before the bend (top and bottom) has no such balancing force being applied and hence has some high loads / forces associated with it and the restraint from the anchor to the pipe and will also include some significant bending moments absent from most of the other anchors.
Whether any of this is actually an issue should be calculated by the program for equivalent stress and reported as a %of maximum allowable stress according to your design code. This is a pretty hunky pipe for the size and pressure it is taking so has a lot spare for other stresses. It's the last support at the top and bottom which will see some fairly heavy forces and if they fail or allow any movement then the effect will ripple up the pipe.
does that make sense for you looking at the actual report / numbers?
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Mine shaft piping stress analysis
The net force on each anchor is balanced by opposing compressive forces imposed by piping either side of it. The high loads are NODE loads, not ANCHOR loads.
I just should have asked for a rstraint report, that would have cleared things up. My apologies for the alarm I might have caused. Now the magnitudes of the NODE loads and the actual forces on the restraints make sense to me. It looks like the stress analyst is doing things correctly - now that I realize what I should have caught on to. My bad.
RE: Mine shaft piping stress analysis
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Mine shaft piping stress analysis
As I understand the proposed solution (anchors every 6m) is oversized but yet acceptable. But still I have few more questions.
The displacement 0,17mm at the bends is negligible?
Between the two anchors shouldn't be there something like an expansion joint or a spring?
At a previous post LittleInch you wrote "I would have thought vertical supports every 15 to 25m and horizontal guides would have been enough".
So as to understand why the solution is oversized..which is the maximum permissible load per anchor or the maximum displacement at the nodes.
I want to thank all of you gents for your valuable help.
RE: Mine shaft piping stress analysis
Between the anchors the pipe is acting like a spring - that's why the forces at the node / within the pipe as so high.
Permissible load will vary in each case as to what is practical / possible. I've seen anchor loads at pipelines coming into a plant in the several hundred tonne mark - needs an anchor v=block as big as a house. Totally ridiculous and unnecessary in most instances to prevent movements of 40-50mm. Allowable movement usually depends on how much pipe you can flex to reduce bending loads - depend son your piping configuration - 5mm might be too much or 50mm acceptable - it all depends....
At least with lots of anchors the pipe isn't going to flex or bow outwards which could happen if you have anchors too far apart.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Mine shaft piping stress analysis
RE: Mine shaft piping stress analysis
If you are going for multiple anchors and guides then for a 12" pipe 20-25m apart has the right "feel" with guides to limit any deflection or "bowing" to 2-3mm every 5-6m. however miningmans point about the practicality of either installing this pipe as a retrofit or replacing it in sections is also important. You are probably limited also by what the height of your crane is to get the longest section vertical before lowering it down the shaft to be fixed to the wall and to the pipes underneath it - again 20-25m sounds about as long as would want to go, but I don't know how you're able to or planning to install it.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Mine shaft piping stress analysis
RE: Mine shaft piping stress analysis
Have you though about some flexibles instead? There are plenty now in the 8" size which go to high pressure (i.e. 100 bar ish) that you could fix to the side and reel it down the shaft all the way to your pump? Usually very corrosion resistant inside and out. Search for RTP (reinforced thermo Plastic pipe manufacturers. Usually a bit more expensive than steel but you save on the installation and jointing issues.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Mine shaft piping stress analysis
RE: Mine shaft piping stress analysis
Your idea for RTP seems quite interesting..but for a future project because for this one the specs are finalized.
RE: Mine shaft piping stress analysis
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Mine shaft piping stress analysis
that was late in my day when I wrote that.
If you're interested in RTP, ask in the pipeline and piping forum as there are some there who have greater experience of using it than me, but it can come in 1000m lengths and like everything has some pluses and some minuses, but might be worth looking at when installation is such an issue.
hope you understand a bit more now...
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Mine shaft piping stress analysis
I was checking again the report..and a question came in my mind..
The bottom bend is anchored at its curve point..when at the same time the last anchor from the top bend is 0,5m.
I mean shouldn't be anchored at the same point. One info that might help is that I have results for dT=10 & dt=-10.Is this the best way for supporting? The loads/stresses seem ok the displacements are negligible..but
isn't it a bit odd ?
RE: Mine shaft piping stress analysis
RE: Mine shaft piping stress analysis
RE: Mine shaft piping stress analysis
Not odd at all.
Ambient / installed.com temp won't change much but operating depends on the temperature of your water flowing through it. At least down a mine you haven't got solar gain.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way