Sec VIII Div. 2 Discontinuity Analysis

[jgibbs22]

Hi Everyone:

Hopefully this is a simple question...

Where does the 2010 ASME Section VIII Div. 2 Code deal with discontinuity analysis for the head/shell area of a vessel? I have a horizontal cylindrical vessel with spherical heads. The 95 Code was much clearer (in my view) on how to handle the analysis. Any insight would be great, thank you.

Jason

 

[TGS4]

Part 5. Or you could just follow the Design By Rules in Part 4.

 

[jgibbs22]

TGS4 Thank you for the reply. I am having a little issue with finding the specific section that goes through this analysis for a "typical" clindrical layered shell to hemispherical head that have different wall thicknesses. Any guidance would be appreciated.

 

[TGS4]

What you are asking for is not explicitly provided for you in Part 5. What is provided is the means to evaluate the stress analysis (however it is that you calculated it). If you are looking for a thin-shell discontinuity-type analysis, I would recommend Timoshenko's Thin Shell Theory books.

Why are you not doing this type of evaluation to Part 4?

 

[jgibbs22]

TGS4, I apoligize if I am not being clear in my question. I would like to do the analysis using Part 4 of the Code, but I am having trouble finding the specific section in part 4 that is dealing with shell to hemispherical head discontinuity stress determination. I thin kit is the shell to conical transistion, but it is not anywhere near as clear as it was in the 1995 Code. Could you provide some direction here?

 

[TGS4]

OK - I think I follow you now.

If I understand you correctly, you have a cylindrical shell that you have calculated its thickness per 4.3.3. And you have a hemispherical head whose thickness you have calculated per 4.3.5. And you want to now check to see if the local membrane stress as well as the local membrane-plus-bending stress is within acceptable limits at the discontinuity? And you're doing this because in the pre-2007 Editions of the Code, you were provided with formulae in Appendix 4-7 and you wanted to do the same thing?

 

[jgibbs22]

TGS4:

You got it! I assume that the new Code looks at this local stresses for Code acceptance, but I am having issues finding specifically how the Code calls out doing it like previously.

 

[TGS4]

The old Code looked at discontinuity stresses only in the context of an Appendix 4 assessment. The old Appendix 4 has been replaced by Part 5.

If you are using the design-by-rules of Part 4, then this type of evaluation is not required (BTW, it wasn't required in the old Code, either, if you sized the wall thicknesses using the old AD-200 rules, either).

 

[jgibbs22]

TGS4:

Thank you for the info! Then I guess the only question I have left is this: If I use part 4 to analyze my vessel, would section 4.3.11 apply to analyzing the transition from the shell to head, or do you not even have to look at the local discontinuity stresses if doing a design by part 4?

4.3.11 Cylindrical-To-Conical Shell Transition Junctions Without a Knuckle
4.3.11.1 The following rules are applicable for the design of conical transitions or circular cross-sections
that do not have a knuckle at the large end or flare at the small end under loadings of internal pressure and
applied net section axial force and bending moment. Acceptable conical transition details are shown in
Figure 4.3.8.

 

[jgibbs22]

TGS4:

Not to get off topic, but if you did not use the thickness equation in AD-200 back in the old Code, that was the only time you had to look at discontinuity stresses like the head/shell transition?

 

[TGS4]

If you're designing to Part 4, then you don't even need to worry about the local discontinuity stress. For your condition, 4.3.11 is not applicable.

To answer your second question - you are correct.