Hello Borzki,

In truth, I must do my job in accordance with EN13480-3. I did not specify this at the beginning, since the SIF for the butt weld looks the same in both codes. If I understand correctly in the latest B31.3 revision, appendix D is no longer available. And instead you have to use B31J and there is a SIF for reducers: 3.1 Concentric or Eccentric Reducer Meeting ASME B16.9 In general, with regard to the reducer, here, in my opinion, everything is obvious on a small diameter, increased stresses clearly arise, which must be taken into account in the SIF. Type B reducer has a transition to a cylindrical section SQRT(Dt), so I set the thickness of the reducer at this point to be different from a straight pipe. Otherwise, it is impossible to appreciate the benefits of increased thickness for stress reduction. But I set the SIF in the reducer unambiguously. In this regard, in CAESAR II there is a conflict situation for EN13480, the fact is that there SIFs are included into two tables H1 and H3. The first table does not have a weldolet SIF, and the second does not have a reducer SIF. If you switch CII to the second table, then the reducer will be left without SIF. Therefore, working with EN13480, you have to check the SIF and sometimes set them manually.

As for the butt weld, both codes say to use the SIF for the butt weld for thin thicknesses. Those, if strictly comply with the code, then for thicknesses less than 5 mm, according to EN13480, you must always set SIF=1.8 Which looks a bit conservative. In EN13480 this SIF is not a mismatch function as in B31. But even if you calculate SIF according to B31, it is still difficult to evaluate mismatch, since mismatch will always occur during welding, and even more so for seamless pipes. Therefore, if we strictly follow the code, not taking into account that the butt weld is already incorporated into the theory, then we must apply the SIF for the butt weld. However, we do not. Taking in to account that SIF for butt weld are still present in the codes, I would like to clarify for myself in which cases we are obliged to apply it.

Best regards Pavel