The weld neck flange, abbreviated as WNF, is a flange type that is usually used with pipes, as opposed to pressure vessels. The design of the flange allows for a full penetration weld at its base where it connects to the pipe.  This weld can be X-ray inspected for quality control.

Weld Neck Flange Standards

ASME Standards

• ASME B16.5 - Pipe Flanges and Flanged Fittings: NPS 1/2 through NPS 24 Metric/Inch Standard
• ASME B16.36 - Orifice Flanges
• ASME B16.47 - Large Diameter Steel Flanges: NPS 26 Through NPS 60 Metric/Inch Standard
  • Series A / MSS SP-44
    • For general use
    • Bolt circle diameter is larger than Series B
    • NOT interchangeable
  • Series B / API Std 605 (cancelled)
    • For compact use
    • Bolt circle diameter is smaller than Series A
    • NOT interchangeable

Weld Neck Flange Sizes - 1/2" through 24"
	Raised Face & Flat Face ANSI Class 150, B16.5 (in) ANSI Class 300, B16.5 (in) ANSI Class 400, B16.5 (in) ANSI Class 600, B16.5 (in) ANSI Class 900, B16.5 (in) ANSI Class 1500, B16.5 (in) ANSI Class 2500, B16.5 (in)		Ring Type Joint ANSI Class 150, B16.5 RTJ (in) ANSI Class 300, B16.5 RTJ (in) ANSI Class 400, B16.5 RTJ (in) ANSI Class 600, B16.5 RTJ (in) ANSI Class 900, B16.5 RTJ (in) ANSI Class 1500, B16.5 RTJ (in) ANSI Class 2500, B16.5 RTJ (in)

Weld Neck Flange Sizes - 26" through 60"
	Series A ANSI Class 150, B16.47 Series A (in) ANSI Class 300, B16.47 Series A (in) ANSI Class 400, B16.47 Series A (in) ANSI Class 600, B16.47 Series A (in)

Weld Neck Flange - Industry Standard
	ANSI Class 75, Industry Standard (in)