Dharmit

what is the D/T ratio of the piping you are working on.

31.3 says:

"Stress intensification and flexibility factor data in Table D300 are for use in the absence of more directly applicable
data (see para. 319.3.6). Their validity has been demonstrated for D/ T ≤ 100"

You may have to look at evaluating the SIF using a Finite Element Analysis.