conservative ASME VIII sec. 2

[tigny]

Hi,

I'm working on stress calculations for a pressure vessel to be designed to API 617, which refers to ASME VIII sec. 2

I created a 3D solid model (Ideas NX).
Assuming fatigue is not a concern,
is it OK (= conservative) to assume that:


if twice maximum calculated stress intensity (tresca) (general or local or peak) for "design pressure + mechanical forces on nozzles" are lower that casting factor time Sm,
AND
if twice maximum calculated stress intensity (tresca) (general or local or peak) for "design pressure + mechanical forces on nozzles+ design temperature" are lower that casting factor time Sps (4-134),

then the design is ok according to ASME VIII sec. 2?

Yours,

Cyril

 

[TGS4]

tigny,

The simple answer to your question is - NO. You need to comply with ALL of the requirements of Appendix 4.

So, take a careful, thorough read-through of ALL of Appendix 4. Pay special attention to the definitions.

When you've completed your design by analysis, I would recommend that you have an engineer experienced in design to ASME Section VIII, Division 2, Appendix 4 review your analysis.

 

[tigny]

TGS4,

I'm into reading the code and also WRC429 to understand and try to apply stress linearization. It's not easy...

I am also reading the 4.136 chapter, which if I understand, proves my design right if calculated maximum stresses (elastic) are below the elastic (Yield) limit.
Is it correct?

Furthermore, may I ask you what you think of API 617 Chap. 1 parag. 2.3.1.1.1 statement that "the allowable tensile stress used in the design of the pressure casing for any material shall not exceed 0.25 times the minimum ultimate tensile strength [...]". (Accordong to API 617, pressure casing shall be designed in accordance with this 2.3.1.1.1 or 2.3.1.1.2 which refers to ASME VIII div 2)

Do you think I can use the maximum stresses from the elastic calculation (FEA) with this API 617 limit to prove the design of my casing?

Yours,

Tigny

 

[TGS4]

4.136 contains the requirements for an elastic-plastic (non-linear) analysis. Further, passing this paragraph only accomplishes the "plastic collapse" requirements of Appendix 4, but not the "ratcheting" requirements.

You mention API 617. I suspect that you are not telling the entire story w.r.t what you are trying to accomplish. Which design code are you working with - actually?

Do you understand the concepts of pressure vessel stress analysis as contained in Appendix 4? I agree that they are "not easy", but a fundamental understanding of the principles of this type of analysis are required. May I recommend that you try to track down a copy of the publication titled "Criteria of the ASME Boiler and Pressure Vessel Code for Design By Analysis in Sections III, and Section VIII, Division 2" published by ASME.

As you probably gathered from trying to read WRC 429, this type of analysis is complex and time consuming. Although you may have good skills at using your FEA program, I would HIGHLY recommend that you find an engineer experienced in pressure vessel stress analysis to work with you and mentor you in the subtle nuances of pressure vessel stress analysis.

 

[tigny]

TGS4,


thank you for pointing out what may be what I lack for this kind of study.

Precisely, the applicable standard for the whole project is the API 617 6th + amendments; the pressure vessel had to and has been designed according to ASME VIII div. 1 for a "U" stamp.

My first concern was to check the forces on nozzles according to 5 times NEMA SM 23.

Since I created a 3D numerical model for this purpose, I wanted to go further and make a complete check of the model according to ASME VIII div. 2.

That's why I came out with those questions.

I'll try to get a hand on the document you told me about; do you know of other documents which would be like a complete, detailed calculation note that comply with div. 2?

Yours,

Tigny

 

[LSThill]

TECHNICAL NOTE:

SDRC IDEA SOFTWARE HAS ASME SECTION VIII Div 1 and Div 2 APPLICATION!

Attitional technical infor may help you is for the header on this form

http://www.paulin.com

SEE Div 2 APPLICATION!


RE: API 618.

 

[TGS4]

tigny,

Although you may have read my rant a few weeks ago about software vs. analyst, after lsthill's post I feel it is necessary to summarize the main points.

1) Do NOT rely on software (ANSYS, IDEAS, anything paulin, etc) to perform the tasks that you are asking questions about, unless you have an in-depth knowledge of the subject.
2) It's the skill of the analyst/engineer that matters.

So, that said, I have to congratulate you on asking the right questions in an attempt to better understand the workings of Appendix 4. Once you've found those documents (or in case you can't), please come back here and we'll discuss. Hopefully you won't fall into the "software" trap that some of the other forum members have.

 

[LSThill]

Technidal Note:

Please review ASME SECTION VIII DIVISION 2 REWRITH DESIGN BY ANALYSIS JAN. 2006. YOU WILL NEED THE PASS WORD AND LOG-IN.

 

[TGS4]

While the design-by-analysis rules contained in the current revision (17) of the div 2 rewrite are, IMHO, vastly superior to the current rules, they come with the added burden of having the analyst know even more than the current rules do.