Manufacturers of UG-44 listed standard components would need CRNs for use in registered piping systems or assemblies of components. This picture shows when the same fittings require registration or not.

Categories of Fittings

The standard flanges, couplings and elbows listed in UG-44 located on the CRN registered UM vessel (not subject to authorized inspection) do not require CRNs. The identical flanges, elbows and couplings located on the registered piping system which will be inspected by an Authorized Inspector do require CRNs. Although it does not make any sense, this is how the rules are currently being applied.