Hi Richard and thanks for your response,

I will try to contact PRG for examining more the 1.65 value but let me be a bit more clear about my query.

My core concern is whether is logical the SIF (in plane / out of plane) calculation of an LR elbow to be different on the same (V12) CII model after I run the B31J since Appendix D and B31J use the same formulas*.

The 1.65 is used for the flexibility factor and is also same in both formulas (B31J and Appendix D).

I do not think it is worth to send the specific model since if you make any V12 CII model with LR elbows and check the in plane and out of plane SIFs and then run the B31J, you will see the different calculated values.

*To avoid any confusion, the B31J on page 2 for in plane and out of plane Sif formulas of welding elbows has an error -I assume- since instead of 0.9/h^(2/3) and 0.75/h^(2/3) for SIFii and SIFio respectively it uses 0.9*h^(2/3) and 0.75*h^(2/3) but later on page 15 it uses the first (/) which is same with Appendix D.
Strangely, I have not seen any acknowledgements for that on the web.

Thanks again for your time and effort,