If you work in the realm of AutoCAD/BIM, consider pairing Intergraph's CADWorx (for routing) and CAESAR II (pipe stress analysis) or Bentley's AutoPLANT + Piping (for routing) and AutoPIPE (for stress analysis). In hospital design, I remember having to download lots of object enablers for either CADduct/MEP (MAP Software) or TSI (Technical Sales International). It seems like the mechanical piping and duct contractors had a preference for using them.
If you are doing compact, custom routings SolidWorks/Inventor/SolidEdge/ProE might be of more use.