FEA OF Pressure Vessels Designed to Div 1

[amech1]

Good day,

I am an ABAQUS novice and I am working on a research project to calculate the reliability of a pressure vessel designed to Section VIII Div. 1.

I would just like to enquire about the ABAQUS outputs for Tresca and VM stresses. Looking at the principal stresses (S11, S22, S33) at each element from the field output via manual calculation the VM stresses that are output from ABAQUS seem to add up using the sigma_vm= 1/sqrt(2) *(sqrt[(S11-S22)^2+(S22-S33)^2+(S33-S11)^2+6*[S12^2+S23^2+S13^2]] equation however the results do not match up for the tresca criterion.

Though seemingly elementary, Can anyone please clarify the following:
1) how does ABAQUS relate the tresca equivalent stress to each element in the descretized model
2) how can I relate the principal stresses for each element to the hoop stress in the vessel (I believe Div 2. clarifies on appropriate procedures for FEA analysis of pressure vessels and linearization of stresses to get components Pm, Pl, etc.for use against div 2. analytical design rules)

Thanks and regards
amech1

 

[TGS4]

Re item #2, see ASME Section VIII, Division 2, Part 5. Ask specific questions about that in either Boiler and Pressure Vessel Engineering forum or the ASME (mechanical) Code forum.

If you are actually doing a research project, may I recommend that you share with us what technical papers you are referencing in that regard? Also, I would recommend that you do both elastic as well as elastic-plastic analyses.

 

[amech1]

Hi TGS4,

Thanks for your response. I will revert to the alternate forum for items surrounding question 2. Just a bit of background on the research. Its based on the applicability of structural reliability methods to design to predict probability of failure and hence reliability of different points along the geometry. This is achieved from the stresses output on the different elements based on loading and comparing them to failure criteria (Vm/ tresca) to create a limit state to calculate reliability.

With respect to reference material, aside from the ASME code Div 1 and selected segments in Div.2 as well as related texts and guidance books reference the code requirements for geometry and design, the PV design material include:
1) Theory and design of pressure vessels, John F. Harvey
2) Pressure Vessel Design and Practice, S. Chattopadhyay
3) Pressure vessel handbook, Paul Buthod

with respect to FEA methods I have been using reference tutorials I have from school notes for elastic analysis as well as the user manual for ABAQUS CAE. Technical papers include (not all authors included in description):

1) Assessment of structural analysis technology for static collapseof elastic cylindrical shells;Steven C. Macy;
2) Finite elements in the analysis of pressure vessels and piping,
an addendum: A bibliography (2001–2004), J,Mackerle
amongst others
- used to get an idea of different modelling techniques in PV applications.

If you wish I can also offer the structural reliability papers at a later date.

With respect to question 1, can you offer a bit more clarity?

Thanks much

amech1

 

[TGS4]

Thanks for your response.

May I suggest a slightly different approach for your research? Starting in about 1995, look at papers that were published/presented at the ASME PVP (pressure Vessels and Piping) Conference. Also, try the ASME JPVT (Journal on Pressure Vessel Technology). If you want practical on FEA for pressure vessels, look at ASME PVP.

Be forewarned, however, that FEA for pressure vessels is not as simple as stresses at a point being compared to some allowable value. You're going to be dealing with stress linearization (on a through-thickness basis) at various points in a model where the allowable value is a function of the location. It is NOT something that lends itself to automation, because it requires engineering judgement. Furthermore, there are multiple failure modes, each of which have different criteria.

Finally, do a search on this site - there have been many good discussions about FEA for pressure vessels.

Two documents that you WILL want to read - WRC 429 and ASME PTB-1.