Intermediate Connection
Class 400 Nozzle Flanges
Intermediate connection flanges for Class 400 service
Class 400 Nozzle Flanges provide intermediate-pressure capability for vessel connections requiring a size reduction at the nozzle. While less commonly specified than Class 150 or 300, the Class 400 rating fills an important gap for systems operating above Class 300 limits but below the threshold that would justify the cost and weight of Class 600.
These flanges follow the same design philosophy as other intermediate connection flanges: the outside diameter and bolt pattern match the larger nozzle size at Class 400, while the bore is reduced to accept the smaller piping. The hub transition profile is designed to minimize flow turbulence and stress concentration at the size change.
Class 400 nozzle flanges are typically found in high-pressure separation equipment, reactor vessels, and heat exchanger channel heads in petrochemical and refining service. Material selection follows ASME B16.5 requirements, with ASTM A105 being the standard carbon steel grade and A182 grades covering alloy and stainless steel applications.
