Load cases for MS pipe

For a main steam piping system with cold spring, I made the load cases as follows:
L1: W (hanger design)
L2: W+D1+T1+P1 (hanger design)
L3: WNC+H (hanger design)
L4: W+D1+T1+P1+H+CS (OPE) (hot case, for restraints calculation only)
L5: W+H+CS (OPE) (cold case, for hanger/support design and equip. nozzle check only)
L6: W+P1+H (SUS) (for stress check only)
L7: W+P1+H+F2+CS (OCC, for stress check, hanger/support design and equip. nozzle check. F2 is the vent forces by relief valves)
L8: L4-L5 (EXP) (for EXP stress check only)
L9: L4-L6 (EXP) (for EXP stress check only)

Question:
1. Are these cases right/enough for the whole piping stress analysis?
2. Are L6,L8,L9 necessary for hanger/support design and equip. nozzle check? I think L6 is not a cold case or field installed case for the MS pipeline, because if P1 is considered in the load case, T1 and D1 should be considered at the same time. Either L8 or L9 is actual load case.
3. How to do analysis after the stress release for a piping system? I mean how to get forces and moments of the restraints under stress released condition?

Harry, you should probably use the recommended load cases except for your OCC case. Anyway, this is how I would set these up:

L1 through L3 as is for hanger design
L4 through L6 as is.
L7: W+D1+T1+P1+H+CS+F2 (OPE) OPE case with vent forces, use for OCC restraint loads.
L8: L7-L4 (OCC) segregated effect of F2, intermediate load case.
L9: L6+L8 (OCC) use Scalar Combination method under the Load Case Options tab. This is your code stress case for OCC.
L10: L4-L5 (EXP) code stress case, the only EXP you need.

Note that the OCC and EXP cases have removed the effects of cold spring. This is because you are not allowed to take a credit for cold spring when computing code stresses (this is why L6 has no CS in it).

Loren... Why CII not automatically take forces if we specified in the input.

If I understand your question, you are asking why doesn't Caesar II set up all the load cases above automatically? The answer is that it doesn't set up occasional load cases because there are too many variables that may dictate different methods of arriving at the correct answer. For example perhaps your uniform load is seismic, or perhaps it is snow load. The seismic may require an SRSS combination whereas the snow load would not. Or perhaps your uniform loads are accelerations on an FPSO, which may require a somewhat different approach than seismic. And F2 as in the above example could be anything, not only a relief load. It could represent a weight that belongs in the SUS case. So, we really prefer that the engineer be thoughtful in the application of correct load cases for their particular application. If Caesar recommended these load cases, many people would not stop to think about the correct application and would simply use whatever Caesar decided, a method we really don't approve of.

Thank you for your reply. But I am still confused that:

1. If I just want to evaluate the reaction forces and moments of the pipeline, is SUS/EXP necessary? I think only actual installed/operating conditions should be considered. But SUS and EXP cases are not actual cases.

2. How to get hot/cold reaction forces and moments after "stress relaxation" phenomenon (or "self-springing" as para 119.2 in B31.1)?

What code is this work being done under??? The B31.1 and B331.3 codes require evaluation of thermal displacements, sustained loads, and occasional loads whose stresses then are added to the sustained loads. So what is the problem here???? Harry read your code book.....

Hi Harry,

1. If I just want to evaluate the reaction forces and moments of the pipeline, is SUS/EXP necessary? I think only actual installed/operating conditions should be considered. But SUS and EXP cases are not actual cases.

If you do not need to calculate primary and secondary stresses you would be right. But you DO need to calculate these stresses. Just go ahead and use the C2 recommended cases and look at ALL the resulting calculated data. BTW there is much discussion on reaction forces and moments on this board and I would suggest that you do a search and read for a while.

2. How to get hot/cold reaction forces

Set up the Caesar II recommended load cases and for the reactions look at the operating case (ope) - look at the restraint summary report for the loadings.

....the moments after "stress relaxation" phenomenon (or "self-springing" as para 119.2 in B31.1)?

The phenomenon that you are referring to is a non-linear occurrence that cannot be duplicated by a linear elastic analysis. If you had a lot of experience in inelastic analysis you might be able to estimate the amount of "effective cold spring" that would creep into the system over a specific period (number of years) and use a C2 model with estimated cold springs placed at "chosen by experience" locations. If the system had intentional cold spring at the time of fabrication and erection it would be difficult to estimate the rate of creep. And just to make things interesting, remember that every piping system ever built in the real world has some amount of unintentional cold spring (construction tolerances of 1/4 inch are typical).

Regards, John