Hi,

I have done stress analysis for a boiler piping, which has only hanger supports in it. I have used the recommended load case available in the loadcase editor, with displacement at the Boiler nozzle. During analysis, I got the displacement around 2 to 3 mm in the SUS case (W+P1+H) throughout the system. But after installation, at some hanger supports the displacement is very high (around 80mm). I wish to know the reason as I am facing this problem for the first time.

Thanks & Regards

Comments please..... :-)

Do you mean a large displacement was found in the real piping system ? If so, you must have got the calc wrong.

Yes Sir. But in the SUS case, the displacements are very less.

You wrote 'AFTER INSTALLATION' Is the piping actually installed with big displacements, or do you mean in an operating case calculation ??

After installation the pipe being displaced about 80mm downwards.

OK, either there is a problem with reality not behaving properly, or your CAESAR II calc input is wrong somewhere.

Perhaps add your calc input to this site ?

How can I attach my file here?

Do not use "Quick Reply".
Instead use "Reply" which open a form with "Post Options" in the bottom; use "File Manager".

Thanks Mariog.

Please find the attached-
1. Sustained displacements generated from Caesar
2. Installed displacements from Site
3. CAESAR II file

Thanks & Regards

Any comments??? :-)

I took a look at your model 50. (You give no indication why you offer the two files - 50 ad 73). Those CAESAR II displacements in the sustained case are similar to the values you state for your system.
Your question is not clear. Your likelihood of useful assistance is directly proportional to your ability to describe an interesting problem.
Your model 50 shows a selection of many constant effort supports. Did you actually purchase all those supports?
(I would've tried rigid Y restraints at a sufficient distance from the anchors to reduce the hanger bill.)

Again, if you wish people's assistance, be sure it looks like you put more work into your question than the work you expect from their answers.

Dear Mr. Dave,

My apologies for not making the question straight.

"73.C 2" is the actual Caesar file with 73mm as vertical displacement at the boundary (node-410). In this case, the SUS case displacement is very less, with all hangers are constant effort supports.

In "50.C 2" file, I have changed the displacement at the boundary (node-410) to 50mm, so that I am getting a "somewhat" similar value. But this is not the real case. In this case I can see Variable hangers in the piping system.

My question is - Should we not design the piping system with complete constant effort supports? Or did I make any mistake in the selection / inputs?

Thanks & Regards

In my opinion, a system with only constant supports (except for your two end conditions) is expensive and susceptible to sympathetic response from a variety of environmental cyclic loads (e.g., flow-induced load or mechanical vibration). But constants (more so than spring supports), if properly sized, will reduce the change in load at those end points with their large vertical (thermal?) growth.

Thanks for your reply.

73mm displacement at node-410 is the boundary condition defined for the system.

Any suggestions regarding the discrepancies in displacement in the Caesar file (73.CAESAR II) and the installed condition (not started operation, hence the variation may not be because of flow induced or vibration)?

Thanks & Regards

I have to agree with MoverZ - it's not that CAESAR II doesn't match the "real world", it's probably that your MODEL doesn't match the real world (or there is a disconnect between program operation and your expectations).
Take node 265 for example. This is a node where a hanger is to be selected. The program picks a constant effort support so it has the "exact" load to balance the deadweight and that load (H) is included in your load case "W+P1+H". For this load case in CAESAR II, the Y deflection of node 265 is zero. That's what you and I should expect. But your reported, from the field, installed position of node 265 is -80 mm.
So, is the hanger out there in field, properly connected? What load is displayed on that hanger? Is it the value predicted by CAESAR II?

Your solution is model specific.
Please report back when you have discovered your correction.