Section VIII Div 2 question
Section VIII Div 2 question
(OP)
From Figure 4-130.1 "Stress Categories and Limits of Stress Intensity", what stress classification(s) should be used for a blind flange that is bolted to a pressure vessel:
Choices are:
Pm - Primary General Membrane
Pl - Primary Local Membrane
Pb - Primary Bending
Q - Secondary Membrane plus Bending
F - Peak
Choices are:
Pm - Primary General Membrane
Pl - Primary Local Membrane
Pb - Primary Bending
Q - Secondary Membrane plus Bending
F - Peak





RE: Section VIII Div 2 question
RE: Section VIII Div 2 question
RE: Section VIII Div 2 question
RE: Section VIII Div 2 question
A flat head, center region is classified as Pm and Pb, but I have been told that there is no membrane stress on a bolted blind flange. May you please explain?
RE: Section VIII Div 2 question
Not to complicate things, but, if you want to be 100% correct, you should calculate Pb with Poisson's ratio ν=0. The increment in stresses due to ν>0 is due to self-constraint in the structure, so it is really a secondary stress (although you won't find this in Table 4-120.1).
prex
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RE: Section VIII Div 2 question
RE: Section VIII Div 2 question
jt
RE: Section VIII Div 2 question
RE: Section VIII Div 2 question
3Sm is in fact 2Y (not really that, but often close to): the limit on P+Q is in fact that it must not cause ratcheting (accumulation of plastic deformation due to load cycling), but plastic deformation for it is indeed allowed.
The safety factor is somewhat given by strain hardening, but in fact it is not necessary: secondary stresses will never cause a sudden collapse before excessive deformation is eventually detected.
prex
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Online tools for structural design
RE: Section VIII Div 2 question
I would highly recommend that you get your hands on a document published by ASME titled "Criteria of the ASME Boiler and Pressure Vessel Code for Design By Analysis in Sections III and VIII, Division 2" - not sure of the publication date. It answers all of the questions that you have here, and many more. If you can't find it, e-mail me at the address on my profile, and I'll see what I can do.