I'm making a 3D tube, and I need to make it 'move' to form something, starting from 0 to the form, that is actually a ring.
If you remember, its something like the old windows 3D tube screen saver:
It's very easy to animate the growth of the pipes if they were simple curves with a bevel shape. You would then animate the Bevel Factor End value to have the shape grow. This would not give you the ball joints you show in the image. You would have to treat them separately.
Another option would be to create the pipes as mesh objects and then use the Mask Modifier in combination with a Dynamic Paint object to reveal the mesh over time. This would give you more flexibility on the shape of the pipe you want to use.
To do this you would: