Stress classification for a Thick pressure vessel at central section

[napoleonm]

A got a thick “Tee” component under internal pressure only, I would like to know how to classify the stress in a section where no influence of the of the gross geometrical discontinuity (the junction bend of the tee) is affecting the stress at the point where I am evaluating the stress.

Basically I can summarize my model as a simple thick cylindrical vessel, under internal pressure, my membrane stress in ok for the allowable stress I have, but there is a bending stress at the point (inside surface where pressure is acting) I am not sure how to classify this stress this last stress; if I classify it as a secondary stress Q my stress levels area ok but if I classify it as a Primary bending stress Pb my stress levels Pm +Pb are out after a stress linearization analysis.

In table 4-120.1 from Div 2, the first section describe:
(Component)-> cylindrical or spherical shell -> (location) shell remote from discontinuities -> (Origen of stress) internal pressure -> (type of stress) general membrane and “Gradient through plate thickness”(bending stress across the thickness???)-> classification membrane as Pm and gradient stress as Q.


Does any body can share opinions.
images SCL are from point B1 to B2

 

[prex]

If the bending stress you find is really the usual gradient of stress through the thickness of a thick cylindrical shell, then the answer is in your citation.
A primary bending stress can only be present in flat heads and flat walls (and in a few, quite rare, other cases).
To clearly understand the classification, you must answer the question: what happens with increasing load, when parts of the section go beyond yield?
The answer for a cylinder is that it would remain circular and straight, and the through thickness gradient would flat out: when rupture occurs, the stress is pure membrane, no more bending.
On the contrary a flat head would become a balloon.

prex

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[TGS4]

Here's the easy answer - don't use linearization (elastic stress analysis) for thick-walled components.

The use of elastic stress analysis combined with stress classification procedures to demonstrate structural integrity for heavy-wall (R / t ? 4) pressure containing components, especially around structural discontinuities, may produce non-conservative results and is not recommended. The reason for the nonconservatism is that the nonlinear stress distributions associated with heavy wall sections are not accurately represented by the implicit linear stress distribution utilized in the stress categorization and classification procedure. The misrepresentation of the stress distribution is enhanced if yielding occurs. For example, in cases where calculated peak stresses are above yield over a through thickness dimension which is more than five percent of the wall thickness, linear elastic analysis may give a non-conservative result. In these cases, the elastic-plastic stress analysis procedures in paragraphs 5.2.3 or 5.2.4 shall be used.

If this is related to your post

So for a thick wall vessel (Rm/t = 1.34)...

in thread794-278484, then your R/t ratio is way too low, and is covered by this rule in the NEW Division 2. (BTW, references to 4-120.1 are referring to, at the latest, the 2006 Edition of ASME Section VIII, Division 2. That's 4-5 years old technology. What is the reason that you are not using the latest/greatest technology out there?)

 

[unclesyd]

Aside from the above here are two papers, one a discussion and the other a lecture on the design of thick wall pressure vessels.

http://highered.mcgraw-hill.com/sit...833/Ch04_Section15_Pressure_Vessel_Design.pdf

http://nptel.iitm.ac.in/courses/Web...pur/Machine design1/pdf/module-9 lesson-2.pdf