ANSI B16.1 Cast Iron Flanges
Class 125 Slip-On Flanges
Slip-on variant for Class 125 cast iron piping
Class 125 Slip-On flanges are designed to slide over the outside diameter of the pipe before being fillet-welded at both the hub face and the back of the flange. This two-weld configuration provides adequate strength for Class 125 service while significantly reducing installation time and cost compared to weld neck flanges.
The bore of a slip-on flange is slightly larger than the pipe outside diameter, allowing for easy assembly in the field. The static strength of a slip-on flange is approximately two-thirds that of a weld neck flange, and fatigue life is roughly one-third, which makes them suitable for steady-state, low-pressure applications but not recommended for severe cyclic conditions.
In cast iron piping systems covered by B16.1, slip-on flanges are widely used in building mechanical systems, water supply mains, and drainage applications. Their lower cost and ease of alignment make them the most popular flange type for routine, non-critical connections in Class 125 service.
