If I am clear on what you are after then you create two pieces of pipe and place in the T position, then convert one into a compound pro-boolean(or boolean)object and pick the other one(probably want to set as union). You can always convert it back to poly and reapply the turbosmooth after, use edge weights to control the seam if necessary.
Thanks for the reply. Unfortunatly I had already tried this (union with ProBoolean) but after the smooth the result was very very bad also increasing the quad-patch prescision in the ProBoolean settings. I think that this could work starting from a square section but not from an exagon section.
The pipeline is coming from a exagon section so I can't change it...
Use a spline to make a right angle, then in the rollout enable it in viewport and set it to radial and number of sides accordingly. Convert this to a poly object and then what you want to do is remove half of one of the cyclinders down the middle(either slice tool or move verts to axis). Use the mirror tool and weld the two halves toegther. Again use the crease tool to keep a sharp angle when applying the turbosmooth.