There is a pressure vessel which has been designed as per ASME Section VIII, Divison 1. Now there is a big nozzle on this vessel for which FEA analysis is done in ANSYS. ANSYS gives you the stress intensity. Now can we compare this stress intensity with the allowable stresses of Sect VIII, Div 2, when the vessel has been designed as per Sect VIII, Div 1?

Hitesh,

No, the allowable stresses for Section VIII Div. 1 will still be applicable, otherwise U-2(g) would be violated. UG-23 gives you some help for the bending stesses.

Does this help?

Thank you Dr. Koelbl for your quick response.
But, Sir i still have a small doubt.

I have found out that Ansys calculates the stress intensity as per appendix 4-120(e) of Sect VIII, Div 2 (please note that I am referring to the older edition of Sect VIII, Div 2). At any given node, Ansys calculates the 3 principal stresses and then gives us the stress intensity which is nothing but the maximum difference between any two principal stresses.

So when the induced stress is calculated as per an appendix of Sect VIII, Div 2, then wouldn’t it be fair to compare this induced stress with the allowable stresses of Sect VIII, Div 2, i.e values from table 2A of Sect II-D.

I have gone through the conversation. I also agree with Dr.Koelbl that you have to use allowable stress of ASME Sec VIII Div 1.
In my opinion the maximum principal stress shall be compared with allowable stress of Sec VIII Div.1. (not the stress intensity of ANSYS)

SRINIVASAN.R

_________________
R.SRINIVASAN
Sr. VICE PRESIDENT
Head, Design and Engineering
PED,ISGEC,
YAMUNANAGAR
HARYANA -135001
INDIA

Well, there is more than only the allowable stress and the stress analysis.

What about the shape of the nozzle, radius of corners, impact testing concept, NDE, QC, fabricating details, etc. ?
all of these aspects form and integral safety concept. Please consider U-2(g) and I recommend to take the advise of your Authorized Inspector.

DK