Q. Is one pipe tracker object in the NaviScan config (which encompasses all 3 coils)? Or do we need 3 x objects in the config (1 per coil)?

A.  One pipetracker object is needed, not more. It encompasses all 3 coils.

Q. What diameter is to be used, the inner metal part of the pipe or the overall pipe diameter including the protecting coating?

A. It needs the outer diameter of the pipe.

With the pipetracker we are looking for the metal parts only, and will draw a circle with the given diameter that have its upper surface at the place where the pipetracker found the metal part.

So the most correct will be to give the diameter of the metal pipe, and then note the knowledge that the concrete part covers the metal by some thickness.