1. Approach 1. Weld material is not added to the model, welds are simulated as weld lines inside and outside the tube.
The stress concentration at the ends of weld lines is reasonable, the value can be high because theoretical value is infinite

2. Approach 2. Weld material is added to the model as a solid ring using Inventor’s Weld feature
Weld ring
The ring is attached to the left tube and deeply penetrates into the right tube
One can see the ring faces sticking out the inner surface of the tube

3. Approach 2. Connections in Simsolid
To see the connections between parts of assembly we use Review Part Connection function on RMB menu on a part
Connection between left tube and the weld ring
Connection between left tube and the right tube
All connections of the left tube
NOTE: there is no connection between the weld ring and the right tube. The ring deeply penetrates the right tube and the connections were not found
The load path goes through the tubes
The weld ring is not stressed much because it is aside of the load path

4. Approach 3 and 4. Weld material is added to the model as solid insertions of two types
Weld insertion
Weld insertion, type 1
Weld insertion, type 2
Connections: areal connections between the insertion and tubes, line-type connections between tubes

5. Approach 3 and 4. Weld material is added to the model as solid insertions of two types
Local stress results are better for the blended weld insertions