Hello eberyone,
I am doing the stress analysis, of 66" lines going from/to the blower.
the is at designP 0.7 bar @DesignT of 240 C, carbon steel with SS steel cladding, 8mm thickness, fluid is flue gas.the line doesn t have valve, just pipe,three elbows.
Inlet coming from the top vertical vessel to the side nozzle (blower).I am having trouble meeting the NEMA SM 23 requirments (limit 1 & 2) eventhough I put an expansion joint (unversal tied bellows) close to the inlet nozzle (blower)the same axis. I am having the large amount of vertical force +Fy perpenducular to the axis of the nozzle, which creates bending momemt around X Axis. the displacment be absorbed 89.70 mm up (y) and 10mm (Z) Z is the longitidunal axis of nozzle. as i understood the 10mm is axial mouvement, 89.70 is lateral movment, that s why i put unversal bellows, but unfortunalty i didn t work well. Overall thermal growth in Y axis.
I hope you understood the problem.
Do I have to meet the Nema Requirements for blowers?
If yes, shall I consider the from the operating case (W+P+T+D) or maximum loads?

Shall I consider the thrust Force (internalPressure*internal section of pipe). Does Caesar calculate this force.
If yes what would be the suitable bellow to absorb in the delta Z axial movment and in the Y axis the lateral deflection (89.70).
Do I have to consider buckling because of internal pressure and thin wall thickness?
I might be wrong somewhere, I would appreciate if you could advise me,and share your knowledges.
Thanks.
Regards,
Yani

forgot to give you the sketch,

I am not an expert, but I think you have to know the following:

1. The Piping Code you are using,
2. The appropriate flexibility factors for a cladded pipe & fittings,
3. The appropriate Stress Intensification Factor for a cladded pipe & fittings,
4. The appropriate equivalent modulus of elasticity for the composite material,
5. The appropriate equivalent coefficient of thermal expansion for the composite material,
6. The allowable stresses for the composite material,
7. The expansion joint you are using (there are tied expansion joints allowing axial movement, i.e. nuts on one side only)
8. How to model your expansion joint properly (read the CAESAR manuals)
9. The dos and donts when using expansion joints (read EJ manufacturer manuals)

I usually compare the operating loads with the allowable equipment loads.
The tie rods will take care of the thrust force, there should be no thrust force acting on your nozzle.
You should consider the possibility of buckling due to external pressure.
You should also consider the need of using stiffening rings to prevent pipe ovalization.
You should also consider the radial thermal expansion of the pipe.


I still have no experience with that kind of pipe, so let us wait for our teachers to give us a hand & often to correct us with our mistakes.

Hope this helps,

Along with Julius2's words I would add that CAESAR II as wells as the B31.3 code has specific caveats concerning high d/t ratio piping see B31.3 Table D300 note 1 !!!!

We have had discussions of clad materials before on this site. Please use the search function to find them, if you need to.

Herr Luf is very much correct about the D/t ratio - for your pipe it is over 200 and the research underlying the B31 Codes generally has been limited to components with D/t less than 100. The reason for this is that at high D/t ratios, the pipe may ovalize and there would then be regions near the most highly curved portions of the pipe wall where local stress effects not considered by CAESAR II would be limiting. This is why julius2 is suggsting you use stiffening rings.

Also, your sketch gives no length dimensions. If one or more of your spools has a length about equal to the diameter, that's another warning that CAESAR II may not be the right analysis tool.

But, in general, I don't think that B31.3 would be my preferred design Code for your application. It could be required by your contract, though.

In the absence of a specified design code, I would much prefer to design this as a large piece of ductwork, with fabric expansion joints. With appropriate fabric materials (silicone rubber), you can easily withstand 240 C. Once you get proper fabric expansion joints specified, the rest can then be designed as a large duct, which in my experience is usually designed under the appropriate structural design code. Of course you then have to anchor the duct to limit the strain on the fabric joint.

Thanks Julius, John for the informations they are very usefull.
Since we are at the proposal stage, that s why I am performing the analysis of such big line. i got an important pressure thrust therfore i have to put such a number of rods to handle these forces.
I would apreciate if you have catalogs, showing the number of rods and their spring rates as well.
Thanks.
Yani

See http://www.pathwayb.com/ they have a PDF you can download and have experienced in large bore stuff.....

Yes Craig you re right..
The reason we are cladding the pipe with ss steel, is because the fluid is corrosive ( flue gas containing wet carbone dioxyde), therefore the metal bellows are required then, in my opinion.
I never had such experience in that big line with bellows. ( we always try to avoid expansion joint).
the layout of the line does not have tees only elbows .
So far analysing the lines, my concern is the design of the bellows, i got large amount of forces and moments. I have to deal with Thrust force and flexibilty. I come up with spring tie rods of 100000 lb/in with four tie rods. otherwise the forces are about 25000 lbs. ( NEMA requirments are not met).
shall i have to consider the max loads or the operating loads?
shall i consider in my analysis design or operating temperature?
Thanks
Kind Regards.
Yani.

In the picture I posted above the large green / grey pipes are actually "thrust rods" to take care of the massive pressure thrust loads. You should work closely with a qualified vendor.... The one fellow in S Africa that follows this forum, "Jouko" strikes me as being competent... and as you can see Senior Flexonics Pathway have also done this sort of engineering and fabrication.

hello,
I ran the analysis of 66" line, with tied universal bellows in order to meet NEMA requirement at the blower nozzle ( < 500Dc =14000lbs), I had to configure stiffness of the bellows.
I put : axial stiffness=200000 lb/in
bending stiff 100 ft-lb/deg
I looked into the manufacturer catalog, i found axial spring rates smaller for 66" ( 1700 lb/in)
as axial stiffness is Kax=F/x
Could any one tell if what's wrong with that???
Thanks
Yani

Thanks John. I will have a look into this in the morning when I am better off. Had something to celebrate. Handed over last manufacturing DRWGs for 7 off 120 to 126" SS bellows running at 590C. 30 DRWGs and some 100 p.of calcs.

Without having model/dimensions I cannot give exact answers but here are some comments:
- my last bellows project was very similar. Started fabric and landed in steel redesign after redesign
- 66" compensators are not cheap. If this line is large portion of the total price you better get the design right.
- In worse scenario you may have to change plant layout
- CAESAR II is quite good with compensators if you model them correctly. There are mistakes in the documentation and the technical recommendation from COADE has had couple misunderstandings. 2 rod universal ends can rotate around one axis quite easily and if this is prevented in CAESAR II model your results are far out.
- Universal compensator is mainly intended for lateral movement. If you force it to take axial movement then the rods do not carry the pressure trust at all. They are limit rods in case of anchor failure
- Vertical force Fy in the blower nozzles is from mass from the duct up to some point in the horizontal section and mainly from the lateral spring force from the universal compensator.
- Lateral spring rate of a universal can be anything. It depends on what elements have been used and how long is the nipple (centre pipe). 66" is normally designed case by case and you do not have them in literature. I made a quick calc. This has 2 layers 0.8 mm, 4 plus 4 convolutions 1000 mm long nipple and the lateral spring rate is only 230 N/mm
- CAESAR calculates the pressure trust if you enter the diameter. In this case the diametre is around 1710 mm and the pressure trust around 160 kN (I used duct OD 1650 mm). Pressure trust is carried by the rods if elements are not compressed and rods loose)
- Instead of universal compensator, which you force to take axial also I would consider 3 hinged compensators in 3 pin system. You should have EJMA code. It has good examples.
- If you go to http://www.jat.co.za/engineeringgallery.htm the second last image is for "universal" with axial compression and the one before that is 3 pin hinge compensator arrangement.
- On this size your rods are about 1 1/4" for stability reasons. Less than 1" is sufficient from stress point of view (2 rods). If you let the rods loose by compressing the unit then it doesn't really matter. If you need to start worrying about rod spring rates then you have wrong design. I have done one design where the strain was ruling (Image is on my site). Problem is the rods connect brackets, which connect to duct. Everything is deforming. How much? You do not know without doing full FEA.
- If your rods are in compression your CAESAR II model is wrong
- Don't forget compensator mass. Hinges, brackets and reinforcing can be heavy.
- For me you need to calculate using design parameters.
- I use metric system. My software calculates also imperial but not my brain.
- It would be best if you had somebody to help who knows bellows design and how CAESAR II works. Not easy to find. There is address below

I hope above helps.

I had a second look into your sketch. You may need combination of gimbal and hinge compensators in modified 3 pin system. On my site second row from bottom has units for such arrangement. You should find similar in EJMA also if I remember correctly. More cost.

It's probably not be the case here but ....

One point to remember when designing a system with several bellows types is the risk that the piping system becomes a mechanism rather than a structure. It's all down to the number of elements, joints and degrees of freedom. If what you have is actually a mechanism .... an infinite number of position will solutions exist within a range of movement, and Caesar will converge onto one of them. An unstable pipe system could result.

Yes. I have had to design these unstable systems. Heavy items supported by bellows elements and hinges or rods. Not nice. In any case CAESAR II is not the correct program for large diameter thin wall but it is a good start. Fast and cheap. Basically what you can do is to use CAESAR II to calculate starting point for bellows design. Design the bellows and then take the system to FEA/FEM to confirm stresses. How to solve stability is an other issue.

Thanks Jouko for sharing lnowledge from your strong experience.
How about the exhaust nozzle, which is typically top nozzle going about 6000mm up then an elbow going 5000mmto the side nozzle of vertical vessl .
the lateral deflection is 18.44mm, and 32mm of axial displacment.
pressure area:23388.21 mm2.
is tied universal bellow suitable?
Thanks in advance.
Yani

Too dangerous to comment without full details, drwg etc. In any case it gets to consulting and normally there is an order somewhere. I do need to eat and therefore have to buy. Shops tend to ask money ;-) You can contact me directly for the work.

Hi Vani,

I dunno u r talking about turbo Blower or ordinary blower. If it is Turbo Blolwer you have to follow the NEMA otherwise u need not.

Dont consider any other bellow other than Pressure Balanced Bellow nearer to Blower discharge nozzle. Because enarmous forces would cause if u consider other bellows.

If it is ordinary Blower, simple bellow is more than enough, but provide proper guide before the bellow, so that to limit the lateral movements.

Hello Moorthi,
thanks for the reply,
the pressure balance bellow are suitable for inlet and exhaust blower. known that is the 66", pressure thrust is large. the pressure thrust does exist in both nozzles inlet and exhaust??
in my analysis at both nozzle, the thrust forceis trying to to pull the nozzle. if I put whether pressure balance or unversal bellows, in either way I have to provide rods to protect against the thrust force.
otherwise if i have to provide the directional anchors which cost more (66").
I would appreciate your thoughts and advices
Yani.

Vani,

consider Inlined pressure balanced bellow, it will not produce thrust and u dont want to put tie rods...the assembly itself contains all those things. Dont compare pressure balanced bellow with Universal bellow, for tied universal only pressure thrust will not come..but if go on tied universal...u cannt arrest the axial movement. Vani, what blower it is...turbo blower or ordinary blower..so that i can give u a better solution.

Before including inline pressure balanced bellows talk to a supplier. There are problems with them. Some issues to consider: cost, size, mass, supporting, internal friction forces are problem on low pressures and normal unit cannot have any lateral deflection. If this is for 66" line the max diam is somewhere 2.5 m and mass easily few metric tn. In these sizes you need to know if the construction has to be double layer. Not many suppliers can make them.

it s an ordinary blower, with low pressure (@10 psi 464 F).
to be conservative , i have to consider NEMA requirements.
the issue right now is to select the suitable and the most economical ones.
have you done similar analysis. ( inlet and exhaust blowers large diametre 66").
In a way that i don t have to follow NEMA, I would appreciate if you do have any allowable loads on blowers (guide lines).
Regards
Yani.

Hi vani,

For the simple blower, you doesn't want to follow NEMA requirements. Just try to reduce the forces and moments at the blower nozzle within 500kg & 500kg.m. Hi..Plz, check the pressure (10 PSI is an huge pressure for blower) Dont consider the absolute pressure in the pressure input column, only you have to consider gauge pressure. I have done the similar analysis for 1800 dia pipe, but for 850 mm wc..i considered only simple axial bellow with proper guides and supports, the loads are come well with 200kg & 200 kg.m but due to pressure thrust i got 1500 kg load in vertical direction, i consulted with the blower suppler for the 1500 kg and they confirmed the stability of blower for the 1500 kg, the system is running good now...vani once check the pressure.

Hello Moorthi,
I wonder how could you reach those loads without meeting NEMA requirments.
May be I am mistaken...NEMA reqts on 66" nozzle Limit 1 : 3Fr+Mr<=500Dc (500Dc=13667) Fr,Mr are lbs,ft-lbs. if I got those loads 500kg ( =5000N=1124 lbs) the system will be perfect.
How did you decrease the thrust force? ( by rods?)
Please advise , I am sure you got more experience than I do.
regards
Yani.