I have a fabricated cross 24"x20". It was made cutting two reducing tees longitudinally and welding both. (Similar to a split tee but in this case we have branches in both sides). In this case what is the best way to estimate the SIF and flexibility. I was checking the new tool in Caesar II for the B31J but there is not a similar configuration. I think SIF can be similar to a reducing tee. Any better aproach? Temperature in this case is 1000 °F.

In normal tees, SIFs are static numbers because of the simplicity of the geometry.

In the proposed geometry, the SIFs would be variable based on the forces and moments coming in from all sides. This would be computationally expensive, and is not available and may not be for quite some time.

The best I could imagine you could do would be to model a single branch in NozzlePro to calculate flexibilities for it, plug them into CAESAR, and then model the cross in a 3d FEA software, applying loads as calculated from CAESAR.

Historically, I would suspect several have taken the SIFs for normal tees, doubled them, and hope for the best.

Thank you Mike.
In my particular case, one branch have only a welding neck flange and blind flange attached, so forces and moments from this side are low.

Then your SIF may be a static number, but you're still stuck with running an FEA on it to be absolutely certain.