SecIV methods of design 1

[Konrad]

Dears,
I need your opinion on right meaning of last 2 paragraphs of the Preamble to SecIV. Do they allow other methods of designing than proof tests when they're not described in SecIV? Can I use Finite Elements under SecIV?

Konrad

 

[CodeRef]

Go ahead and design with an FEA and then Proof Test it.....or.......speak with the AI. Section IV does not cover all possible details of design and construction. Where complete details are not given, it is intended that the manufacturer, subject to the acceptance of the Authorized Inspector, shall provide details of design and construction which will be as safe as otherwise required by these rules. When the strength of any part cannot be computed with a satisfactory assurance of safety, these rules provide procedures for establishing its maximum allowable working pressure. The Authorized Inspector must verify that all required design calculations applicable to the construction have been made in accordance with the Code, and that any questions raised by the Inspector are resolved. The Inspector is not required to check for accuracy of the calculations. The responsibility for accuracy of the calculations lies with the Manufacturer.

 

[Konrad]

CodeJackal,
Actually, proof test is what I wanted to get rid of. The AI is not sure, but I could convince him. The problem is that I am not sure either

Konrad

 

[CodeRef]

Konrad,
My particular answer to this question came from interpretation IV-94-05 regarding minimum wall thickness calculations for external pressure on Section IV tubes compressed to an obround or elliptical configuration for which there was NOT any Code guidance provided.
ASME's response to this inquiry was the same response which I stated for your question.
Perhaps an Intepretation inquiry to the Preamble of Section IV to ASME can clear up your question. I would make the assumption that the reponse would be the same as I stated to you, but you will never know until you request the interpretation.
If anyone else has had any experience with design to Section IV, please respond.

I have encountered this question before from a client and the default answer for them was to perform a proof test. Good Luck in finding your answer!

 

[GenB]

My AI wll not allow FEA only, but in conbination of prooff.
The Code will not allow it either.
if you are making one unit or a few yoiu can save money but if a production run
it is wise to proff to assure yourselfr of the performance.
else how you will findout.
ND Test is mandatory.
genb

 

[Konrad]

GenB
Why would I need to do FEA if I proof-test it anyway?
And why you say the code does not allow it? It looks just vague.
Konrad

 

[CodeRef]

Please note: Allof these answers are suggestions and the AI needs to make the final decision in all matters., With that said, the proof test does not need to be to destruction and you can still use the item after the proof test, provided deformation has not occurred. see Interpretation IV-92-10

The reason the FEA benefits you in addition to the proof test is that you can determine the point at which deformation WILL or WILL NOT occur (depending on your input), therefore you could construct a tighter design knowing that the FEA can determine that point.

Using these two methods in parallel will allow you to gain the advantage to the competition that uses other formulae in determining yield.

In my opinion, proof tests to establish maximum allowable working pressure are intended for designs where the strength cannot be computed with a satisfactory assurance of accuracy. Therefore, if you are able to satisfy your Authorized Inspector that your calculations satisfy this requirement, then proof testing would not be required.

 

[panduru]

Thank you, CodeJackal, for a good post. Since it is obviously such sound logic, it should really apply Sec. VIII Div. 1 design as well. I see no reason why the same approach cannot be taken in that case, when everyone knows that a conservative design by VIII-1 is always an overdesign, and so a pain for the manufacturer.

 

[GenB]

Code Jackal has answered,
note that the AI has the obligation to chosse the Best Eng practice + the Code minimums,
example is the jurisdictions in Canada:
ASME Code is 3rd in line of acceptance,
thus EnG Practice and safety (their Code) is first...
FEA can not proove the results only theoretical.
I have a design of tubesheets in which my calcs are perfect thus my AI wants also design analysis, figure it out..
it means that Code is first then other analysis sufice.
genblr

 

[Konrad]

Thnk you BenB, I just needed to understand whether this things are treated similarily under SecVIII-1 and SecIV. Apparently, it's not analogical.
Konrad