Class D Standard Steel Hub Flanges

AWWA C207 Class D steel hub flanges are rated for 150 psi working pressure and feature a short hub that provides a welding neck for attachment to the pipe. The hub adds structural reinforcement at the pipe-to-flange junction, improving resistance to bending moments and reducing stress concentrations compared to ring flanges.

The Class D rating covers the majority of municipal water distribution pressures, making these flanges the workhorse of waterworks piping. Hub flanges are preferred over ring flanges when the joint is subject to external loads from pipe weight, thermal expansion, or soil settlement in buried installations.

Class D hub flanges are dimensional equivalents of ANSI B16.1 Class 125 flanges for sizes NPS 4 through NPS 24, allowing interchangeability with cast iron valves and fittings in that range. For sizes above NPS 24, the AWWA dimensions diverge from ANSI standards and are unique to the waterworks industry.