To model a hot tap first find out the displacement of the connection point from its installation position to its hot position. This distance is essentially a cut short or cold pull in the new line. Ideally, the new line will be installed with a length to fit up to the hot position and it will be "short" by this distance. So the new element connecting to the existing (hot) line will have the same X,Y,Z length as the distance calculated above. Call out this element as material #18 "Cut Short". Then enter the remaining elements of the new system conected here using the lengths that you will use to install the piping to fit right. Don't forget to reset the material. Set up three thermal sets: for the existing system T1=hot, T2=hot, T3=ambient; for the new system T1=ambient, T2=hot, T3=ambient. Set up three operating cases: L1)...+T1+CS, L2)...+T2+CS, L3)...+T3+CS. L1 is the intial fit up to the hot line and this run will tell you whether you modeled everything right as, except for deadweight sag, there should be no load in the new line. L2 is everything hot and L3 is everything cold. The deadweight run should also include CS.

Give it a try...