Class E Standard Steel Ring Flanges

AWWA C207 Class E steel ring flanges share the same 275 psi pressure rating as Class E hub flanges but use a flat plate construction without a welding hub. The ring flange is welded to the pipe end with fillet welds on both the inside and outside diameters, relying on the pipe wall and weld throat for structural capacity.

Ring flanges at Class E pressures require heavier plate thickness and larger bolting than their Class B counterparts, but they remain less expensive to manufacture than hub flanges because they are flame-cut from flat plate rather than forged or rolled into a hub shape. This cost advantage is most significant at larger diameters.

The use of ring flanges at 275 psi requires careful engineering evaluation of the pipe wall thickness and weld quality, as the lack of hub reinforcement means the pipe wall carries the full bending stress at the joint. For buried piping with significant external loads, Class E hub flanges may be the more conservative choice.