Dharmit,

By doing a search in this forum you will find that this topic has been covered a few times. The most relevant, is "SIF for lateral tee" Borzki 29 Sep 2005. There are a number of references to research papers on this topic and that FEA should be used. A big surprise to me was the reply from Chuck Becht (ASME B31.3 committee member) in this topic thread that stated:

"Laterals have been found in testing and analysis to have a lower SIF than 90 degree branch connections. The opening size is larger so the moment divided by the moment of inertia of the section where the branch connects to the run pipe yields a lower line load than for a 90 degree branch. The B31.3 committee has discussed putting in a simple statement that the SIF for 90 degree branches can be conservatively used for laterals."

I was always told previously by my peers that SIF's for lateral tees are worse than for straight, and a factor such as 2 should be used in the absence of code direction, this before the use of FEA analysis. However, the above statement as far as I know, does not appear in any code or published industry paper, which is what you/we are after. Laterals have been used for many decades, so I wonder why the codes would not want to address them if in all cases the SIF's for laterals are less than for straight tees and that by simply assumming the same would be conservative.

So the best bet in my opinion is to get the tee analysed by FEA to get the actual SIF's especially for such a tee as yours which is very close to the limit of the code's applicability, and way beyond the size range and D/t ratio of the tested tees that the B31.3 code SIF's are based upon.

Regards
Mike