Using the <em>link</em> above, perform a search of this discussion forum for SIF. There are a number of discussion threads on this topic.

The short answer is that there is nothing officially published by the codes (except for the French code, CODETI) on anything other than 90 deg tees. Your best bet is FE analysis, unless you find something else in the literature (such as PVP or ASME), as mentioned in the above posts.