1) How you determine the code break point and/or decide to apply B31.1 or B31.3 for steam and condensate piping?

2) Boilers use Boiler codes and Boiler external piping clearly uses B31.1.
What does Nonboiler external piping mean and where does it start and end?

3) Opinions to date:
B31.3 starts at the first block valve on the distribution system at the generation plant.
B31.1 is designed and best suited for steam and condensate piping.
Both codes can be used, pick the one best suited to the situation.

Thank you
Arthur34