Slow down a bit. Are we talking ASME BPV Code or ASME B31 Piping Code???
I concur with JLSeagull. First of all all pressure equipment fabrication and installation may or may not be regulated by a local government. That regulation will tell you what legal and safety requirements are (eg. what code of construction is aceptable, vessel stamping requirements). That regulation may also tell you what the inspection requirements are (eg. third party invovement/certification etc)
Taking purely the codes:
For ASME BPV involvement of Authorized Inspector in fabrication and certification of the vessel/boiler is a requirement for ASME stamped vessels/boilers.
For ASME B31.3 Piping, the involvement of Owner Inspector in pipping fabrication is mandatory.
For ASME B31.1 BEP PP stamped, involvement of Authorized Inspector in piping fabrication and certification is mandatory.
Read ALL of UG-117 it tells you how to obtain an ASME Cert and it also contains the requirment for an agreement with an AIA. You CANNOT build and stamp an ASME vessel without an Authorized Inspector involved.
If you don't have a Code book buy one, if you have a Code book look in the index its a good place to start.