Fitting Guide

Definition and Details of Socket Weld Fittings ASME B16.11

Socket Weld fittings general

A Socket Weld is a pipe attachment detail in which a pipe is inserted into a recessed area of a Valve, fitting or flange. In contrast to buttweld fittings, Socket Weld fittings are mainly used for small pipe diameters (Small Bore Piping); generally for piping whose nominal diameter is NPS 2 or smaller.

To join pipe to Valves and fittings or to other sections of pipe, fillet-type seal welds be used. Socket Welded Joints construction is a good choice wherever the benefits of high leakage integrity and great structural strength are important design considerations.

Fatigue resistance is lower than that in butt-welded construction due to the use of fillet welds and abrupt fitting geometry, but it is still better than that of most mechanical joining methods.

Some details of Socket Weld fittings

SW Fittings are family of high pressure fittings are used in various industrial processes.

Types of socket weld fittings by class, size and wall thickness

Description Class Designation
3000 6000 9000
Elbows 45 and 90 degrees,
Tees, Crosses, Couplings,
End or Pipe Caps
1/2 - 4 1/2 - 2 1/2 - 2
1/2 - 4 1/2 - 2 1/2 - 2
1/2 - 4 1/2 - 2 1/2 - 2
Pipe Size
by Wall Thickness
SCH 80 / XS SCH 160 XXS

Plugs and Bushings are not identified.
They may be used up through Class 6000 NPS

Advantages and Disadvantages of Socket Weld fittings



The purpose for the bottoming clearance in a Socket Weld is usually to reduce the residual stress at the root of the weld that could occur during solidification of the weld metal, and to allow for differential expansion of the mating elements.

Fittings for Socket Weld Pipe systems

A Full Coupling, joins pipe two pipe or to a nipple etc..

The Half Coupling can be directly welded to the run pipe, to make a branch connection.

Reducing coupling
The Reducing Coupling joints two different outside diameters of pipe.

Reducer insert
Socket Weld Reducer Inserts are manufactured to MSS SP-79. They enable quick and economic combinations of pipeline reductions to be made using standard Socket Weld fittings.

Union (MSS SP-83)
It is a screwed joint design and it consists of three interconnected pieces: two internally threads and a centerpiece that draws the ends together when rotated. Unions should be screwed tight before the ends are welded to minimize warping of the seats.

Elbow 90°
This Elbows make 90° changes of direction in the run of pipe.

Elbow 45°
This Elbows make 45° changes of direction in the run of pipe.

Tee Straight
This Tee makes 90° branch from the main run of pipe.

Crosses makes 90° branch from the main run of pipe.

Cap (End Cap)
Seals the end of pipe.

Remark(s) of the Author...

A simple manner to make a 1/16" Gap...

  • Have you ever seen a Socket Weld contraction ring?.
    It is a split ring that is engineered and designed to give a pre-measured 1/16" minimum gap for socket welds. Made from a certified stainless steel, and resists corrosion from chemicals, radioactive materials and water. Once inserted into the fitting the ring becomes a permanent part of the joint. It will not rattle or vibrate even under extreme pressure.
  • Another manner is the applying of in water-soluble board. Make rings with a hole punch with outside and inside diameter of the pipe. Insert the ring into the flange or fitting and after hydrotesting there is no ring anymore.

For both solutions, ask your customer for permission.