Pavel,

In EN-13480, the basic equations (in paragraphs 12.3.2 to 12.3.6) take the SRSS of all three moments and apply a single SIF - which is to be taken from Appendix H.1. This matches the B31.1 (pre-2020) approach.

EN-13480 paragraph 12.3.1 permits an alternate approach, where a more detailed determination of the stresses can be performed by separating moments (in-plane, out-of-plane, and torsion). Here the SIFs should be taken from Appendix H.3. This matches the B31.3 approach.

The CAESAR II configuration switch changes which set of stress equations (and SIFs) are used to determine the stresses in the piping system. If the switch is set to use separate moments, then the SIFs from Appendix H.3 are used. If the switch is set to SRSS the moments, then the single SIFs from Appendix H.1 are used.

What you could do is set the switch to use the SRSS moments and the SIFs from Appendix H.1. Take the reported SIF value for the reducer and manually specify this value on the reducer element in the input. Then change the switch back to use separate moments. The setting of the reducer SIF and its origin should be documented in the "title page" of the input for documentation and review purposes.

I hope this helps.