ASME Sec VIII div 3

[Alpete1430]

Hi all,

Greetings to everyone in the forum.

I have a question regarding ASME Sec VIII Div 3 Fig KD-240 where the figure speaks about stress linearization (linear elastic analysis).

I'm doing an analysis in ANSYS Workbench 13.0 on a pressure vessel considering testing conditions and therefore applying test pressure (1.5 times the working pressure). And I've derived the Primary membrane (Pm), Bending (Pb) and Peak stresses (Q) by constructing a path geometry across the shell thickness and evaluated the linearized stress intensity across the path.

Can I compare the Primary membrane+Bending+secondary stresses (Pm+Pb+Q) to twice the yield of the material (2Sy) for Maximum Operating Conditions. (refer dotted lines in the fig) as per the fig KD-240, in sec VIII Div-3?

If yes, How can I derive the secondary stresses (i.e. Q) in Ansys Workbench Which only gives the info on Primary membrane (Pm), Bending (Pb) and Peak stresses (Q) only?

Or are the Primary membrane (Pm)and Bending (Pb) {which are got from ANSYS WORKBENCH software} inclusive of secondary stresses (Q)?

Thanks in advance,
Alpete1430

 

[TGS4]

You must be referring to an old edition of Div 3. The current edition disallows elastic analysis completely. Why would you be using elastic analysis for a Div 3 component?

 

[Alpete1430]

Dear TGS4,
Thank you for your feedback.

The Design Allowable Stress Paragraph of ASME Sec VIII, Div-2 talks about the following for hydrostatic test pressure condition:

Pm ≤ 0.95Sy
Pm+Pb ≤ 1.43Sy (for Sy ≤ 0.67Sy)
Pm+Pb ≤ (2.43Sy - 1.5Pm) (for 0.67Sy < Sy <0.95Sy)


And I can derive Primary membrane plus bending stress from ANSYS workbench.

Can I use the above given allowable stresses?

PS: I'm analysis a valve which is seeing a pressure of 15.3MPa (1.5 times the design pressure)

Thanks in advance.

 

[TGS4]

Can I use the above given allowable stresses?

I don't know your specific circumstance other than what you have shared. That is a decision that is up to the engineer certifying the MDR and the AI.

What happened to the Div 3 question?

 

[jte]

... And if Section VIII Div. 1, 2, or 3, then why hydrotest to 1.5x MAWP?

Sounds like it is time to hire a qualified consultant who is experienced in the particular design being contemplated.

 

[BenStewart]

A bit late, but...if you're now using Div 2 I would suggest that (typically) a valve geometry does not lend itself to demonstrating protection against plastic collapse from a linear-elastic analysis, see 5.2.1.2 and 5.2.1.3.