Basis of Principal stresses in ASME Div2 1

[modern53]

Dear All,

According to ASME Div 2 (5.3.2)for the elastic stress analysis method summation of the principal stresses must be lower than 4S. From a CAESAR model there are two different type of loads, operating and sustain. If i want to calculate the principal stresses by a software (e.g nozzle pro) what type of the loads (operating or sustain) should i use in nozzle pro?

Thanks in advance

 

[TGS4]

The Code is a little vague on which load case is required to evaluate 5.3.2. Therefore, I would perform this check in all of the load cases listed in Table 5.3. (You are checking all of the load cases in Table 5.3, right?)

 

[LSThill]

modern53 (Mechanical)
REFERENCE: ASME PTB-3-2010 SECTION VIII-Division 2 Example Problem Manual
READ: ASME Div 2 (5.3.2) Problem E5,3,2 Elastic Analysis page 5-19

 

[modern53]

LSThill,

In the example you mentioned there are no external forces and moments. only internal pressure considered.

 

[jtseng123]

Per code it says "5.3.2 .....The sum of the local primary membrane plus bending principal stresses shall be used for checking this criterion."

In CAESAR II, operating = sustain + thermal.
The code says "primary membrane plus bending", that in terms means "PL+PB", no "Q" invloved. And thermal load is "Q",
so you shall use "sustained loads" from CAESAR II.

The sustained loads are from pressure and dead weight, which indeed will generate primary membrane and bending stresses.

My two cents only.

 

[TGS4]

jtseng123 - you are incorrect. External loads from attached piping can generate primary local membrane stresses - regardless of whether the piping loads are "thermal" or "sustained".

(As an aside - you may ask yourself - how does this guy know. Well, I wrote several papers on this topic. These papers were referenced when I re-wrote/clarified the requirements in the new Division 2. I am currently undertaking a project to clarify/re-write Table 5.6, so as to avoid the confusion the jtseng123 has indicated, by comparing two completely different Codes with completely different intents/purposes...)

 

[jtseng123]

TGS4, Thanks again. I have been confused so many years doing pressure vessel regarding the table PL, Pb and Q, and many people so called "pressure vessel engineers" whom I know of not even getting close to know what it is. I believe when I retire one day, claiming doing pressure vessel for the whole life and designing and purchasing hundreds of them through the world, I will still say "Hey ! I really do not understand that table". What a shame but I, like many other people, live with it.

 

[TGS4]

No problem. Maybe I'll peer-review the revision here. I suspect that there are lots of people in the situation you describe.

 

[EnergyMix]

TGS4, that would be a valuable service. I gave you a star just for considering doing it.

 

[TGS4]

Not to de-rail the discussion, but you bring up a valuable point - EnergyMix. Sometimes, I find that the Code Committees are a rather insular and insulated bunch of groups. There is real value in "public" consultation. In this new technology age, peer-review or crowd-sourcing is now taking place in the blogosphere or in discussion boards such as eng-tips. I will definitely give this a try.

(Of course, after the Committees go through it, it may look nothing like what was peer-reviewed initially here, but I guess that the nature of consensus work...)

 

[EnergyMix]

Back many years ago, Marc B. of TVA (full name not used as I don't have his permission) used to peer review the ASME III Code sections among his peers that worked there at the time. However, that was limited to the people that he knew in his work setting. It sometimes made for interesting discussions. In this day, it's possible to reach a much wider audience and to be able to see how other engineers are going to interpret what is "perfectly clear" to you. If you're able to, it would be a great service.