I have a pipeline connected using threaded connections at the end of each spool. The question is: Should I check the bending stress at each connection by defining SIF (Threaded type no.11) or should I define the SIF manually.

Kindly note that the line size is 6" with 3" branch connections.

Thanks in advance.

It would be much simpler to specify a threaded connection since both pipes framing into the node will receive the SIF. If you define the SIF by hand, you will have to explicitly set the SIF on both pipes framing into the joint. (But if there's one pipe in and one pipe out and no restraint at the joint, the loads used to calculate stress will be equal and opposite at that joint so, while sloppy modeling, there will be no need to get the "right" stress on both sides of the joint node.)

Thanks a lot Dave, that is helpful.