how to simulate the threaded joint in solidworks without real threaded joints

If you are looking for a more accurate mechanical simulation for pressure response, I'd recommend the following:

1. calculate the thread engagement area at connection
2. create split line features on both pipes for that area
3. apply your pre-load/torque to each split line surface

You can also look into applying a press-fit condition at your joint, using the same thread engagement area from above.

-M