Socket Weld Flange

on . Posted in Pipe Flange

swf flange 1The socket weld flange, abbreviated as SWF, is similar to a slip-on flange, except only one fillet weld is made to the flange and pipe.  Pipe is welded to socket weld flanges by inserting the pipe into the socket and backing the piping out between 1/16” and 1/8”.  This is to prevent the expanding pipe on the inner side of the weld from expanding when headed and cracking the weld on the fitting.

Socket Weld Flange Index

There are a couple different methods for ensuring that the pipe has enough clearance when welding.  The first is by inserting the pipe fully into the flange and marking the pipe.  Then remove the pipe so that the marking has moved 1/16” to 1/8” and make the weld.

The other method is by using a tool called a gap o’let.  A gap o’let is a springy spacer installed between the pipe and the flange.  The use of gap o’let should be considered when designing a piping system.  The reason for this is over time, the gap o’let may dislodge itself from the flange and travel downstream of the flange.

Socket weld flanges were originally designed for small diameter, high pressure pipe.

This flange is available in flat face, raised face and RTJ type connections.  Socket flanges that are compliant with ASME B16.5 are only available in the following combinations:

  • ANSI 150 – ½ to 3
  • ANSI 300 – ½ to 3
  • ANSI 600 – ½ to 3
  • ANSI 900 – ½ to 3
  • ANSI 1500 – ½ to 3 ½

There are other flange sizes and classes available by most manufacturers but it should be noted that only the sizes listed above are compliant with ASME B16.5.


Socket Weld Flange Advantages and Disadvantages

  • Socket weld flanges provide high structural integrity because the pipe is inserted into the socket of the flange, and then a fillet weld is applied on the outside.  This results in a strong and durable connection.
  • The smooth bore of the socket weld flange allows for good flow characteristics, minimizing turbulence and pressure drop in the system.
  • Socket weld flanges are relatively easy to install, and the welding process is simpler compared to some other types of flanges.  The socket provides a self aligning feature, making it easier to achieve proper alignment during welding.
  • Socket weld flanges are suitable for high pressure applications, and they are commonly used in systems with elevated pressures.
  • Socket weld flanges have a relatively compact design compared to some other types of flanges, which can be advantageous in tight spaces or where space is a constraint.
  • Once a pipe is welded into a socket weld flange, it is challenging to make rotational adjustments.  Precise alignment during installation is crucial to avoid misalignment issues.
  • The welding process can introduce thermal stresses into the material, which may be a concern in applications involving temperature variations.  Proper welding procedures and material selection are essential to mitigate these concerns.
  • The welding seam and the crevice between the pipe and the flange can be vulnerable to corrosion.  Adequate corrosion protection measures, such as coatings or proper material selection, are necessary.
  • While socket weld flanges are suitable for many applications, they may not be the best choice for critical applications where factors like frequent disassembly or high cyclic loading are involved.
  • Inspecting the welds in socket weld flanges can be more challenging than inspecting some other types of flanges.  Non-destructive testing methods may be required for thorough inspection.
  • The fillet weld in socket weld flanges can create stress concentrations, which may be a concern in high stress or high vibration environments.


Socket Weld Flange Datasheets

The datasheets we have on this site are shown below.  For simplicity sake, only datasheets that adhere to B16.5 are shown.  ASME B16.5 covers flange dimensions from ½” to 24”.  For sizes larger than this (ASME B16.47 Series A & B), please visit our flange datasheets page.

ClassRaised Face
ANSI 150 Socket, ANSI Class 150 (in)
ANSI 300 Socket, ANSI Class 300 (in)
ANSI 400 Socket, ANSI Class 400 (in)
ANSI 600 Socket, ANSI Class 600 (in)
ANSI 900 Socket, ANSI Class 900 (in)
ANSI 1500 Socket, ANSI Class 1500 (in)
ANSI 2500 Socket, ANSI Class 2500 (in)


Piping Designer Logo 1 

Tags: Pipe Flange