Hello all,

In a previous topic (Diference between SIF,SCF and KI) it was said that the correlation between the stress intensification factor and the ASME NB stress indeces was C2K2/2=i=peakstress/2nominalstress. In other words it was said that the product C2K2 its equal to the peak stress.
For a FEA this peak stress its the Von Misses equivalent Stress?.

In some papers of PVP the stress index its calculated by the ratio of a stress intensity and the nominal stress. The stress intensity its defined as the greatest diference between the principal normal stresses: StressIntensity=máx(|S1-S2|,|S1-S3|,|S2-S3|), where S1, S2, S3 are the principal normal stresses.

So im confused, i need to calculate CAESAR II and K2 using the Stress Intensity to calculate the SIF? or i can take and maximun equivalent stress (such as Von Misses equivalent stress) and use the equation shown above?

Thanks in advance

Joohane,


Pray tell what code are you working under?

Mr. Breen i´m very thankfull for that valuable piece of information. Mr. Luf i´m working with the B31.3 code.

I´m a student and i´m trying to develop the stress intensification factors for some non standarized pipe components. I´m working with a FE program for stress analysis. Now i have this doubt i dont know if i have to calculate the Von Misses Stress or the Stress Intensity for the calculation of the factors CAESAR II&K2 for the final calculation of the SIF.

Best Regards

Hello Johane,

If you are working with the B31.3 Code, you are looking for information on B31 Stress Intensification Factors (SIF's). These are unique to the B31 Codes for Pressure Piping. The B31.3 equations in which you will find SIF's applied are classic beam theory equations for calculating bending stresses and these equations use the Tresca theory of failure.

The ASME B31 Codes for Pressure Piping DO NOT use CAESAR II and K2 factors. There are very fundamental differences between the ASME B31 Codes for Pressure Piping and the ASME B&PV Code, Section III, Subsections NB, NC and ND. If you attempt to mix the concepts of B31 with the concepts of Section III, in your work you will become very confused and you will not achieve what you are attempting to do.

It is clear from your questions that you are still confused about the differences between all these "factor" definitions (again, some of them are not used with the B31 Codes). Be VERY sure that you completely understand what B31.3 SIF's really are and also understand that when using beam theory with B31 equations and B31 SIF's you will not be calculating true elastic stresses. Read again the reference that I gave you above in this thread. Go back to the thread in which you originally asked these questions and read again Dr. Becht's definition of B31 SIF's.

There is a WRC Bulletin that describes how to develop SIF's for standard or non-standard pipe fittings and components.

Bulletin WRC-392 Developing Stress Intensification Factors: I - Standardized Method For Developing Stress Intensification Factors For Piping Components ; II - Effects Of Weld Metal Profile On The Fatigue Life Of Integ - 10/30/2003 E.C. Rodabaugh ; G.E. Woods and E.C. Rodabaugh

Good luck with your work

Regards, John.