Every fitting on a registered pressure vessel or a registered piping system needs a CRN unless it is exempted. B51 clause 4.2.1 provides an exemption:
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All fittings shall be registered… unless they form a part of a boiler or pressure vessel that is subject to inspection by an authorized inspection agency…

This exemption is universal in its scope – exempting any fitting. In practice provincial jurisdictions will only use this exemption for items found in ASME VIII-1 table UG-44 which covers:

  • B16.5 flanges
  • B16.9 wrought butt weld fittings
  • B16.11 forged fittings
  • B16.15 bronze threaded fittings
  • B16.20 metallic gaskets
  • B16.24 cast copper alloy pipe flanges and fittings
  • B16.42 ductile iron pipe flanges
  • B16.47 large diameter flanges

All other items not found on this list require CRNs for use on pressure vessels. Contrary to the B51 standard, CRNs are also not required for these same fittings when used on a UM vessels which are not subject to inspection by an Authorized Inspector. This exemption does not apply to Assemblies of Components.