Sec VIII Div 1 calculation formula
Sec VIII Div 1 calculation formula
(OP)
Hello,
I have a question regarding a shell calculation. Why is code using different formulas if it is outside or inside diameter?
If long. stress formula is Sl=P*Rm/2t, why is code using P*(Ri-0.4*t)/2*E*t.
Or if Circ Stress is Sc=P*Rm/t why it is used P*(Ri+0.6t)/E*t
Why is, for the longitudinal stress Rm=Ri-0.4*t and why is Rm=Ri+0.4*t for the circumferential stress?
And shouldn't Ri always be used if it is internal pressure?
I have posted same question on Pressure vessel forum, but I did not get the answer.
I have a question regarding a shell calculation. Why is code using different formulas if it is outside or inside diameter?
If long. stress formula is Sl=P*Rm/2t, why is code using P*(Ri-0.4*t)/2*E*t.
Or if Circ Stress is Sc=P*Rm/t why it is used P*(Ri+0.6t)/E*t
Why is, for the longitudinal stress Rm=Ri-0.4*t and why is Rm=Ri+0.4*t for the circumferential stress?
And shouldn't Ri always be used if it is internal pressure?
I have posted same question on Pressure vessel forum, but I did not get the answer.





RE: Sec VIII Div 1 calculation formula
RE: Sec VIII Div 1 calculation formula
It is not a job interview and I am working in pressure vessel industry for some time. I did number of calculations and never questioned why formulas are different. I just took them for granted.
RE: Sec VIII Div 1 calculation formula
Because the surface to which the load (pressure) is applied differs between the two case the formulas themselves must work differently. This will be the case regardless of whether thin shell or thick shell theory is applicable.
However, as shown in your original thread the two formulas agree "in the limit", ie: when the required thickness equals the nominal thickness the ID and OD formulas produce equal numerical result.
RE: Sec VIII Div 1 calculation formula
My conclusion is that the Code formulas are using Rm:
For circ stress:
Rm=Ri+0.6t
Rm=Ro-0.4t
For longitudinal stress:
Rm=Ri-0.4t
Rm=Ro-1.4t
Why?
RE: Sec VIII Div 1 calculation formula
Try:
"Theory and Design of Modern Pressure Vessels" by Harvey
"Pressure Vessel Design Handbook" by Bednar
"Guidebook for the Design of ASME Section VIII
Pressure Vessels" by Farr and Jawad (ASME Press)
Tom Barsh
Codeware Technical Support
RE: Sec VIII Div 1 calculation formula
I would add Timoshenko "Theory of Plates and Shells".
RE: Sec VIII Div 1 calculation formula
Click on the link below and then go to Web Based Search, and there enter the following ADAMS accession number:
ML040150682
This will open up a link to a PDF file that gives you a Short Course on ASME Boiler and Pressure Vessel design by John Mooney, starting at page 93. Up to page 93 is all about repairs (NBIC) to same (if you want to read it)
Here is the link:
http://www.nrc.gov/reading-rm/adams/web-based.html
RE: Sec VIII Div 1 calculation formula
RE: Sec VIII Div 1 calculation formula
Does a vessel with an MAWP of 15 psig, 1" ID, 2" OD have no circumferential stress? I have 30 psia acting on a 1*pi perimeter with an opposing stress of 15 psia acting on a 2*pi perimeter. So, deriving the thin (ahem) wall free body diagram, if I take a section cut on a 180° section, I have no resultant force on the cut surface. No force means no stress.
I think I just came up with another interview question!
jt