For a branch connection 12” NB x 2” NB (45 deg) I am getting different expansion stresses with following two input options.

1) SIF (I) and SIF (O) keyed in values (from FEA) for all three elements forming a junction without defining type of connection
2) SIF (I) and SIF (O) keyed in values for all three elements forming a junction & defining RF type connection along with pad thickness.

SIF values in Caesar II output report are same as the keyed in values but bending moment for branch is higher for 2 nd option.

Why this is happening?

Does bending moment calculation of branch takes into account the type of connection?
Is this anything to do with effective section modulus of branch (319.4.4 Eq (20) of ASME B 31.3)? It seems like this formula is not taking into account the RF pad and type of connection.

Then why is the difference in caesar II outout report for expansion stresses?

Your valuable time is highly appreciated.

Cheers,

The reduced branch uses an effective section modulus. If you don't call it a tee, CAESAR II will not apply the effective section modulus.

Here's how you can confirm... test the model with a full size branch. I believe you will get the same bending moments.