Long Weld Neck Standard
Class 150 Long Weld Neck Flanges
MSS SP-97 long weld neck flanges for Class 150 service
Class 150 Long Weld Neck flanges per MSS SP-97 combine a standard B16.5 Class 150 flange face with an extended forged hub that replaces the separate nozzle pipe and pipe-to-flange weld. The hub length is specified to project through vessel insulation or to reach the required nozzle projection from the vessel shell.
At Class 150, LWN flanges are commonly used on atmospheric and low-pressure storage tanks, heat exchanger shells, and column nozzles in refining and chemical processing. The one-piece forged construction eliminates the heat-affected zone of the pipe-to-flange weld, which is often the weakest point in conventional nozzle assemblies.
Standard hub lengths range from 6 inches to 18 inches, with custom lengths available to suit specific vessel configurations. The bore is machined to match the connecting pipe schedule, and the hub taper provides a smooth transition that reduces stress concentration at the flange-to-hub junction.
