Dear Dave & Richard.

This is regarding inputing of loads in CAESAR II WRC 107 Module.

Case : 1

Sustained: W+P1

Expansion: T1. Pure Thermal loads,

Occasional: WIN1, Pure occasional loads
(pure seismic loads or pure
wind loads etc.,)


Case 2

Sustained: W+P1

Expansion: W+P1+T1

Occasional: W+P1+T1+ WIND1

In both cases, which one is correct one to input in Caesar II wrc 107 module.

Requesting your response at earliest.

Thanks
L&T Chiyoda.

Any help.

Hello Durga Ji,

The Case 1 is correct. You only want to specify the pure occasional loads. The WRC 107 module will do the summation of pure occasional loads with the sustained loads.

Though for the Expansion case I would not use T1, but set it up as a range between SUS(W+P1) and OPR (W+T1+P1).

Good question.

Thank you very much

About "expansion case", I second TGS4 opinion in https://www.eng-tips.com/viewthread.cfm?qid=438540
To find out more about TGS4 see https://becht.com/blog/authors/trevors

In fact Div VIII-2 clarified the point.

TG54 suggestion to qualify all the nozzle loads as Sustained-type is excessively conservative.

In fact, regardless the local stress calculation method (e.g. WRC/analytical or FEA), the stress Qualification/Check shall be performed as per ASME VIII-2 part 5 requirements.

ASME VIII-2 post-2007 Editions require the external piping loadings induced on nozzles "by the restrained free end displacements of the attached pipe" (e.g. the external loadings developed by the restrained pipe expansion/contraction) to be considered for Pm (general membrane) and PL (local membrane) Code stress qualification ONLY within the Nozzle Reinforcement Area limits, as defined by ASME VIII-2 para. 4.5.

Outside the Nozzle Reinforcement Area limits, Pm (general membrane) and PL (local membrane) Code stresses should be qualified without external piping thermal expansion/contraction loads consideration.

Resultant Secondary Pm+Pl+Q Code stress shall include external piping thermal expansion/contraction loads' effect + gross-structural discontinuity concentration effects throughout the whole shell-nozzle junction.

When local stress analysis is performed by FEA approach using PRG Software (Nozzle Pro, FE Pipe, FE 107 modules), the software algorithms perform the required assessments and computations in accordance with Code requirements.

When local stress analysis is performed using Caesar II WRC107 module, then:

1) One typical run as per Case (1) as described above shall be performed, with ASME VIII-2 Stress Indexes ACTIVATED, and WITHOUT Pressure Thrust Load included (e.g. ASME VIII-2 Stress Indexes are already taking account of longitudinal pressure stress concentrations);

2) One additional run with Operating Loads (Weight+Pressure+Thermal = W+P1+T1) defined as Sustained-type, WITH Pressure Thrust Force Considered and ASME VIII-2 Stress Indexes excluded, in order to check Pm and Pm+Pl membrane stresses only. Any Pm+Pl+Q overstress should be ignored in this case. In addition, if Reinforcing Pad outside edge is located beyond the ASME VIII-2 Reinforcement Area, any potential Pm and Pm+Pl overstress at the Pad peripheral edge (e.g. Pad-Shell outside joint) shall be ignored.

Similar approach should be employed for local stress analysis as per WRC297 Bulletin.

I attach table 5.6 of VIII-2. Just read it and conclude yourself.

Hello All!!!

This is a very informative discussion. In NozzlePro software this particular code requirement can be activated under Load Case Options then check the box "Assume restrained free end displacements are primary loads within nozzle limits of reinforcement". But of course this is the membrane component of the stress and not the bending component of stress. As we all know the membrane component of stress is more risky since the whole through-thickness section experience the same stress level and therefore will reach the failure stress at the same time and will lead to global plastic collapse. While the bending component of stress is linearly varying through the thickness for a thin walled member with the surface having the highest stress. Therefore, the surface will experience yielding first while some portion are still under elastic stress. In Nozzle Pro this is reported as Qb which is approximately less than 2Sy. But this is not under ASME VIII requirement I forgot what ASME Code it is. We may consider this as plastic hinge or local plastic collapse?

Anyway, just sharing my thoughts. Just correct me if I have some wrong statements.

Cheers!!!

Another way to tackle this in case we fail in this code requirement is to run an Elastic plastic analysis considering the strain hardening effects and large deformation effect. If the solution converge, then the force-moment equilibrium is achieved. But this type of analysis is quite tedious. The only question for this high plastic strains will be how many cycles we can safely cycle it. A simplified elastic fatigue analysis considering plasticity correction factors Ke is available in ASME. I don't know if a more detailed elastic plastic cyclic stress analysis can be done. I haven't gone so far in that field of study.

Any other opinion is highly appreciated. Corrections are welcome.


Cheers!!

One can find on web an interesting presentation of WRC 107 by Mr. Delaforce in CAUX 2014. I think is in line with the traditional view of WRC usage.

But the truth is WRC does not touch the stress category. And probably would be hard just reading WRC 107 to understand the difference between 1kN shear force by piping sustain case and 1kN shear force by restrained expansion of piping, since WRC 107 assumed that shear force is transmitted to the shell "entirely by membrane shear force". Yes, traditionally we make a difference saying one is originated by force and other is strain controlled and self-limited- but here this criterion appears to be so thin, thinking that sustain load is due to the mass and gravity acceleration which are still stable in this world.
Anyway, my remarks will not solve the problem and probably the future is performing elastic-plastic analysis. Here my doubts would be that probably after performing such analysis we'll be ready to forget that engineering is not only calculation but also having wisdom to move potential troubles in places where risk is not so high.

Thanks Mariog for that very nice opinion. In my own opinion, this elastic-plastic analysis has still many uncertainties like proper boundary condition, etc., so I'm not so confident to rely on this method especially if my system will likely to experience high number of cyclic loading. It's still better to design a system with sufficient factor of safety to have a reliable system rather than pushing the system to it's limit. I can sleep soundly at night.


Any other opinion is highly appreciated.

Cheers!!!

Hi Mandeep,

I know that this is the old threads, but I have a question for you. Could you please tell me how to get the pure occasional loads from Caesar II?

As I understand like this: (OCC)L3=L2-L1 (pure occasional load)

L1: (OPE)W+T1+P1
L2: (OPE)W+T1+P1+F1
F1 is reaction force from PSV.

I need pure occasional loads to input in NozzlePro for nozzle load verification.(The PSV is very close to the nozzle).

Please advise if I am correct?

Thanks,