Doubt ASME VIII Div. 2: Design By Analysis FEA

[FPPE]

Hi everyone,

I have a question regarding ASME VIII Div. 2 Design By Analysis.
Is it possible to completely design a vessel using FEA?

I know that asked in this way may seem reductive, I try to elaborate on what I mean.
I am interested in designing (when possible) to save on thicknesses without affecting safety of course. I think it is well known that ASME VIII Div. 1 abounds in this sense, while codes such as EN13445 allow to obtain smaller thicknesses.

Now, taking advantage of Design By Analysis, is it possible to get a given thickness without considering any formula after stress linearization validation? All this taking into account a complete design with wind, earthquake, loads on the nozzles, stress on the saddles (all if possible through FEA).

Example:

Through the formula of the thickness of division 2 (t=D/2[Exp(P/S)-1]) I get 10 mm, and considering all the other loads I would need 14 (I'm assuming of course). Now, is it possible that doing a complete finite element analysis taking into account all the loading conditions I can get 12 mm or less than 14? And if it is possible, can I do it or the code prohibits it?
Also, in some cases is it possible for convenience and speed of design to use both Part 4 and Part 5 for the same vessel?

I hope I didn't ask a stupid question.

Thank you for your answers

 

[GD2]

FPPE,

That is exactly the intent of DBA.

Cheaper vessel at more engineering work.

GDD
Canada

 

[NRP99]

You can use combination of Part 4 and Part 5 for Class 1 construction. For class 2 construction you need to only use Part 5. But read carefully ASME Sec VIII Div 2-Part 4-Para 4.1 and ASME Sec VIII Div 2 - Part 5 - Para 5.1.1.3.1.

1-B.2.10 Class 1 Vessel – a vessel that is designed using the allowable stresses from Section II, Part D, Subpart 1, Table 2A or Table 2B.
1-B.2.11 Class 2 Vessel – a vessel that is designed using the allowable stresses from Section II, Part D, Subpart 1, Table 5A or Table 5B.

 

[jmec87]

Note that regulators in some jurisdictions (such as ABSA in Alberta, Canada) have long required any components adequately addressed by the rules to be designed by rule and not by analysis (I don't know if this has recently changed). I recommend verifying with any regulators from whom you require design approval that they will accept full design by analysis and checking if they have any special requirements for it.

https://www.absa.ca/media/1210/ab-520-finite-element-analysis-fea-requirements.pdf

 

[TGS4]

I agree with all of the above posters, who have provided excellent advice. I would also add that it would be foolish to go through all of that effort and not use the Elastic-Plastic Analysis Method for demonstrating Protection Against Plastic Collapse. If you're going the full-on DBA route, use EP. And you have to be very careful mixing and matching DBA and DBR.

 

[FPPE]

Thank you all for your excellent answers!

Out of curiosity, I would like to ask if you have ever had any experience in this area with SolidWorks Simulation and what you think about it.

In the specific case of elasto-plastic analysis I have no experience at all, I would try if the software allows me.

 

[r6155]

Can any checker do their job normally when using 100% FEA?

Regards

 

[TGS4]

r6155- yes, it is done all of the time. The checker needs to be equally skilled in FEA.

 

[IdanPV]

FPPE,
I have an experience in the area of DBA of pressure vessel (vessels with CRN as well) using SolidWorks Simulation.
I have made a study to compare the results of PTB-3 with SolidWorks, results show good match.

What exactly you want to know or ask?

 

[MrPDes]

For Div 2 Class 2, section 5.1.1.5.2 says that Part 4 Design by Rules can be disregarded (i.e. the minimum calculated 10mm thickness in your example can be disregarded in favour of a thinner Von mises derived minimum stress).

Div 2 Class 1 and Div 1 App 46 make Part 4 rules mandatory. Section 5.1.1.5.1 says "Rules in Part 5 shall not be used in lieu of rules in Part 4." 2.3.3.1(a)(2) also infers this. This means that the 10mm minimum thickness based on the design by analysis hoop stress calc is mandatory. Part 4 Nozzle Reinforcement and Saddle design rules would also be mandatory.

Div 1 Appendix 46-4(a) says "Division 2, Part 5 shall not be used in lieu of the design thickness requirements of Division 1 or Division 2, Part 4."