Thanks for all explications!
I modeled the junction with FE-Pipe software (PRG) and I obtained necessary rezults: flexibility and SIF. I modeled in FE-Pipe also a part of my piping system and I put all limits conditions (I read them from the CAESAR output). I obtained stresses according ASME Sec. VIII, but for B31 in expansion case too. I introduced the SIF and the flexibility of the bend in the CAESAR model and I compared the rezults. They was very close. Because the nozzle has a free end (is a thermo-rezistance) there was not high values for ASME stresses

Thanks for all your advices!

Best regards,
Dragos Aron