Hi everyone,

I am quite new to Caesar II and I have been reading the provided documentation. However, from time to time I run into a few questions.

I currently have modelled a simple pipe that goes in the x+ direction, then y+ after a small bend, then z+ after another bend. The pipe is anchored at both ends and hot air runs through it at ambient pressure. The pipe is also supported before the first bend (Y+ type restraint)

Having run the static analysis, I have noticed that the force on the support was quite high and I though that a spring support situated after the second bend and pre-stressing the pipe (cold state) in tension rather than compression would ease the force on supports and anchors and stresses in the bends.

I am not sure how to model this support. I currently have a YSPR at that node. The spring stiffness (Stif field) is 4000 lbf/in, the force applied at cold state (F field) is 8000 lbf, so the spring is pre-compressed by 2 in, finally, the spring is bottomed-out in the Y- direction (so 0 for "x" field ?)

I want this support to correctly model these behaviours :
- The force acts in the Y+ direction (is the positive 8000 lbf already representing this?)
- The spring is bottomed out in the y- direction
- After 2 in. of Y+ displacement, the spring will no longer be compressed

Have I correctly modelled this support?

Also, the documentation mentions : "X/Y/Z SPR can be preceded by a (+) or (-)" which it cannot. What is up with that.

P.S. : I have version 5.2

Thanks in advance

Alain,

I do not think you will get an answer for your application here easily. I guess that you are very new in pipe stressing. Even though your application is very simple you still need a supervision on what you are doing. This kind of things can not be easily explained in the forums. The supervisor should give you directions for you to understand the thermal expansion concept, stifnesses, behaviour of supports etc...

Please do not get me wrong. I do not want to discourage you from the start, but this job requires some years of experience under suppervision unfortunately. Do not rely everything you read on the forums either, you need to filter them carefully.

Kind regards,

Ibrahim Demir

Ibrahim,

I noticed by looking at a lot of threads that the kind of problems that surface here are complex and design related. I also am aware of the need to rely on the experience of my company's senior engineers. This particular kind of support was, in fact, proposed to me by one of them.

That being said, I do have a bachelor's degree in mechanical engineering and do understand such concepts as thermal expansion, stiffness, shear, torsion, bend stresses in beams and pipes, finite element analyses, rigidity matrices, ...

All I want is for one of the many experts on here with Caesar II to take a minute of their time to help me translate the physical behaviour I understand into the appropriate steps with the software. As I said, I've run into some contradictions by reading the documentation and experimenting with the software.

Thank you for your consideration.

Please do understand that the software is a tool, like a screw driver. So you need to know how to handle it.

I am not saying that you can not do the analysis. However,it is really difficult to explain some kind of experiences from the distance, there are many thick books about them, and still difficult to explain many of them on the pages.

So the supervisor who suggested the spring hanger should stay next to you and watch together what is really happening, and give you additional directions depending on the pipe behaviour under those conditions.

OKAY;

1. First; you do not mention about the pipe diameter, temperatures, straight distance between pipe start and end, and the directional distances.
2. You do not talk about the load types other than the hot air. Do you have occasional loads? Are you running the pipe stress for thermal and sustain loads only?
3. Under what conditions you are having problem with the hanger? Is using hanger really right solution for your problem? Check displacements under problem loading, and see why this is happening? Is the selected hanger the right hanger for your application?

We can not answer those due to the reasons above. We have some idea, but whatever we say will be open to interpretation.

So there is no easy answer. I suggest your supervisor should stay next to you for about 10 minutes even less to see and solve those.

I hope this helps, and please do understand that I do not want to hurt your feelings, these are friendly suggestions only. You have a good background but you still need experience.

Kind regards,

Ibrahim Demir

Thank you Ibrahim, I will keep your suggestions in mind.

If you still want further detail about my model, here it is :

- The pipe has an outside diameter of 44.75 '' and a thickness of 0.375''
- The entire pipe is made of material 1.4435W except the FIRST bend which is made of 310 stainless.
- The pipe goes straight along x+ for 20' 5'', then a 5' 6'' radius bend, then straight along y+ (vertical) for 9' 6 11/16'', then a 5'6'' radius bend, then straight again making a 7.5 degrees angle with z+ for 9' 6 11/16'' and finally finishing with a 5'6'' bend curving the pipe in the y- direction.
- When looking at the XZ plane, the angle between the 1rst and last straight sections is 97.5 degrees.
- The pipe is anchored at both ends (before the straight x+ section and after the last bend)
- All bends are double flanged
- There is a 4'' thick mineral wool insulation around the pipe.
- Hot air at 500 degrees far. flows through the pipe at ambient pressure.
- The total mass of air in the pipe is 32.4 lb.
- Total mass of the system is about 15 000 lb.
- If supported before the first bend (Y+ type support), the second bend will have risen 1''.
- If supported like described, the Y+ support takes on 17 620 lbf.

Thats about it

You are working with large diameter pipe within small distance.

I do not think you need to use a spring hanger in this application. You need a rigid vertical support in the vertical rise somewhere close to/or on the upper elbow. The pipe is very stiff and it will introduce large bending moments to the fix ends and elbow connections. These fixed ends must be equipment and they will have sort of allowables at these locations, so you need to watch them when playing with the location of the rigid support.

It seems an iteration is required for the right location of rigid support. However, it may not give you what you are looking for. So you need to change the pipe route to get more flexibility to the systems.

Another thing is D/t ratio. Yours exceeds 100, and you need to be more carefull with the fitting flexibilities and SIFs. Using flanges on both sides of the elbows are to prevent buckling mainly under the bending moment action, however they need to be checked whether they give the required stiffness against buckling and providing the joint tight against leak. Your problems are getting more complicated than what your supervisor thinks.

The analysis with pipe stress software may not be giving you the right answer. You may need to probably model this with an FEA software with the right plate/shell elements to see how exactly the pipe shell behaves.

In case the fixed end bending moments are higher than the alowable or you are getting problems with the bends or their connections, you may be forced to use expansion joints against the end expansions/rotations.

You may use FE-Pipe for the proper analysis I guess.

Good luck.

Ibrahim Demir

Thanks Ibrahim, you've given me a lot to think about.