A Bit About Weldneck Flanges

Everything You Need to Know to Pick a Weldneck Flange

What is a Weldneck Flange?

Weldneck Flanges are designed to be buttwelded to a beveled pipe creating a very strong connection. These flanges are frequently used in high pressure and extreme temperature systems. The buttweld transfers stress from the flange itself into the connected pipe. Weldneck flanges are specified by:
  • Size
  • Bore
  • Class
  • Material
  • Face
  • Origin

Size and Bore:

The size of the weldneck flange corresponds to the nominal pipe size of the connected pipe.
Bore refers to the thickness of the pipe wall. Weldneck flanges are typically found in standard (STD), Schedule-10 (S10) and Extra Heavy (XH).
To specify a weldneck flange you must match the size and bore to the nominal pipe size and schedule.
A mismatch in either of these criteria can change the fluid dynamics and ultimately weaken the system.


Class describes the pressure and temperature capacity of a given flange.  150# to 1500# are standard in weldneck flanges.
To specify determine the pressure and temperature requirements of the system and refer to this class guide.


Weldneck flanges come in Raised Face (RF) or Flat Face (FF) options. Face refers to the structure of the back face of a flange. A RF flange has a lip inside the ring of bolts while a flat face flange, as the name suggests is perfectly flat.
If you are replacing a flange in an existing system, you must match the face type of the corresponding flange. A raised face flange should never be mounted to a flat face flange.
RF flanges are typically used in higher pressure/temperature systems.


Weld neck flanges are most often made of carbon steel, but stainless steel and aluminum are also available.
Stainless steel is used when superior corrosion resistance is needed. Weldneck flanges are made out of 304L and 316L to improve weldability. {Link to stainless steel article}
Aluminum is a fantastic option when weight is a factor.


All pipe fittings are classified as domestic or imported based on their country of origin. Domestic fittings are manufactured in the USA and are typically painted green. They satisfy “made in the USA” requirements.  Imported fittings provide a lower cost alternative.


Gaskets and Stud Bolts

Gaskets and Stud Bolts are needed to install a flange into a system.


The type of gasket you need is determined by the face of the flange you choose and the temperature and temperature of the system.
Full Face Gaskets are used with flat faced flanges.
Ring Gaskets or Spiral Wound Gaskets are with raised face flanges.  Spiral wound gaskets give superior seal in high pressure/temperature systems.
Gaskets are made of non-asbestos material and are sized by the pipe size and class of the flange.
Stud Bolts
Gaskets are compressed between two flanges with stud bolts. We offer carbon steel stud bolts with a standard black finish and with a Teflon coating. Teflon coated stud bolts have superior corrosion resistance when compared to a standard stud bolt.

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