Just my personal opinion...

That 45 deg forged tee is it a Latrolet, actually?
If yes, I would definitely use Caesar II Latrolet SIFs from CII internal database. They are established as per Bonney Forge reference data, and Bonney Forge is a well-known and reputed international manufacturer.

In this way, speculations are avoided and I believe SIFs values are realistic enough.

In general, as pointed out above, the actual geometry of the fitting is un-known. Any FEA model would mean to speculate, more or less conservatively.

If the Client/Owner is not happy with such approach, ask him to indicate what approximate skewed intersection to assume for FEA assessment, but warn him/her that an un-reinforced intersection might be excessively conservative and might yield to high stresses and consequently high demands for layout flexibility and maybe sophisticated support arrangement.

Regards,

Regards,