What is a Socket Weld?

Welding pipes can be rough, especially if you don’t have the patience or know what you’re doing. That’s why knowing how to form a socket weld is super-important.

What is a socket weld? A socket weld refers to the weld that joins specific pipe fittings like reducers, tees, and elbows with pipes. The pipe is permanently joined to the recessed region of the joint with a socket weld. The pipe fittings connected by this method are called socket weld pipe fittings.

Read on to get further details on socket weld pipe fittings and their advantages as well as shortcomings. 

Socket weld pipe fittings

Socket weld fittings are used for connecting pipes. A pipe is inserted into the recessed part of the flange, valve or fitting. Fillet type seal welds are applied to join fittings with pipes. Socket weld fittings are an excellent choice for a wide range of applications since they have high leakage integrity and high structural strength. These are crucial aspects that must be considered while designing piping networks. 

Carbon Steel A105 Forged Pipe Fitting, Full Coupling, 1/2" NPT Female x 1/2" Socket Weld, 3000 PSI

While requesting such fittings, you will have to mention OD dimensions, along with the thickness schedule (or pressure rating). 

Socket weld pipe fittings are referred to as SW pipe fittings. Therefore, SW couplings, SW tees, SW elbows, and other such parts come under the rubric of SW pipe fittings. 

Socket weld fittings usage

Since these fittings have high-pressure ratings, they are suitable for a wide range of industrial applications. 

SW pipe fittings, such as reducers, tees, and elbows, can be installed in pipelines to transport flammable, toxic, or hazardous chemicals safely with a lower risk of leakage. These fittings are suitable for processes where leakages can prove to be dangerous. They can be installed in piping networks as connections of a permanent nature. 

SW pipe fittings are engineered to facilitate excellent flow characteristics. They have high quality since they are often manufactured per the ASME and ASTM specifications and standards. These standards and specifications cover essential technical details for reliable performance, such as tolerances, markings, pressure ratings, temperature ratings, dimensions, and materials. They also mention requirements for various forms, such as 

  • Seamless pipes
  • Seamless tubes
  • Forged parts
  • Bars

And other items while specifying their mechanical and chemical properties. 

Similar to butt weld pipe fittings, socket weld fittings are also subdivided according to alloys, such as alloy steel, carbon steel, and stainless steel. Depending on the type of applications, you can choose from SW flanges, couplings, reducers, reducing tees, socket weld tees, SW elbows, and other connections according to the material type. 

Different kinds of socket weld fittings

Here is everything you need to know about different types of socket weld fittings. 

Full coupling

This connection joins two pipes together. Full couplings have threads at both ends to connect both pipes.

Half coupling

Stainless Steel 316 Cast Pipe Fitting, Half Coupling, Socket Weld, MSS SP-114, 1/2" Female X Plain

While similar to a full coupling, the main difference here is that half couplings have threads on one end only, while full couplings have threads on both ends. The unthreaded end of the half coupling is usually welded or fastened via other means to piping. 

Reducing coupling

This pipe fitting connects two pipes of different diameters. The reducing coupling has different widths on both ends so that the pipes of different diameters can be connected. 

Socket weld reducer insert

These are manufactured according to the applicable ASME and ASTM standards. These parts allow the economic connection of pipes of different diameters. 

Socket weld union

This part comprises three interconnected pieces. There are two internal threads as well as a centerpiece, which brings the ends closer as a result of rotation. For this reason, socket weld unions must be screwed tightly before the welding of both ends. As a result, seat warping will be minimized. 

Socket weld elbow

Stainless Steel 316 Cast Pipe Fitting, 45 Degree Elbow, Socket Weld, MSS SP-114, 3/4" Female

Socket weld elbows come in 2 different forms: 90 degree and 45-degree designs. There are the short radius and long radius models made by the forging process. This socket weld connection has a vital role to play in pipe networks. It is used to change the direction of fluids. 

Socket weld tee

Parker Weld-Lok 4 JW-SS Stainless Steel 316 Socket Weld Tube Fitting, Tee, 1/4" Tube OD, 0.19" Bore

This connection allows a branch to be connected at a 90-degree angle between two
pipes running in the same direction. Socket weld reducing tee has a similar concept. The key difference being that, as the name suggests, a smaller diameter pipe can be attached at 90 degrees between two pipes traveling in the same direction.


Sockolet,Forged,1/2 in,316 Ss

The sockolet is employed for the same purpose as the threadolet and the weldolet. It is used to weld a smaller diameter pipe with a larger diameter pipe. The main difference is that the sockolet contains a socket that can be welded conveniently. This socket is within the olet. This connection allows a 90- degree direction change, and it possesses higher strength to withstand higher pressure. 

Socket weld cross

Anvil 2153 Forged Steel Pipe Fitting, Class 3000, Socket Weld Cross, 1" NPT Female

This connection enables a 90-degree direction change for branches connected between 2 pipes going in the same direction. 

Socket weld cap

Anvil 2157 Forged Steel Pipe Fitting, Class 3000, Socket Weld Cap, 1-1/2" Female

As the name suggests, the socket weld cap is connected to the end of a pipe to seal it. 

Socket weld flanges

Stainless Steel 304/304L Pipe Fitting, Flange, Socket Weld, Class 150, 10" Pipe Size

SW flanges are employed for relatively small diameter pipes at the higher pressure. The flange shape has a recessed shoulder towards the inner diameter. This allows the pipe to be correctly connected with the fitting. Welding is used to joining flanges and pipes permanently. The advantage of this piping connection is that it permits excellent flow characteristics. 

There are different SW flange designs, such as ring tenon joint, flat face, and raised face. They have a variety of pressure ratings that can go up to 2500#.

Socket weld pipe fitting advantages

  • The pipe has to be beveled to make it ready for welding.
  • In general, there is no need to make tack welds to align pipes properly. The design of these fittings enables proper alignment. 
  • Socket weld pipe fittings can be substituted for threaded fittings since they have a much lower risk of leakage.
  • Weld metal does infiltrate into the pipe bore.
  • Installation costs for socket weld fittings are lower as compared to butt weld fittings. This can be attributed to the more relaxed dimensions requirements and the fact that that there is no need for special machining in socket weld fittings, unlike butt weld parts. 

Socket weld pipe fitting disadvantages

  • Socket weld pipe fittings aren’t suited for the food industry because they don’t allow complete penetration, and they have crevices that aren’t easily cleaned. 
  • Socket weld pipe fittings must have a specific expansion gap between the shoulder of the socket and pipe. 
  • Internal crevices and expansion gaps associated with socket weld fittings lead to corrosion. Hence, socket weld pipe fittings are not suitable for radioactive or corrosive substances as the buildup of these materials at the joint may lead to maintenance and operating problems. 

Making the expansion for socket weld pipe fittings

There is a simple way in which the expansion gap of 1/16 inches can be made. 

The socket weld contraction ring must be considered for this purpose. This split ring is engineered specifically to provide the minimum gap necessary for socket welds. These are made of stainless steel and have high corrosion resistance. The ring can be easily installed in the fitting so that it becomes a crucial part of the connection. It does not produce vibrations even under high pressure. 

Key differences between butt weld and socket weld fittings

For socket weld fittings, the applicable standard is the ASME B16.11. This standard enables the insertion of a pipe within the recessed region of the joint. The pipe and the joint can be easily cut to the necessary shape. There is no need to bevel the ends or to make any other preparation. The surfaces need to be kept clean to allow smooth welding and installation. 

The ASME B16.9 is the applicable standard for butt weld fittings. Since their ends are welded onto pipes, the thickness needs to be the same as that of the pipes. The ends of joints need to be beveled. 

There are also specific key differences between butt and socket weld fittings as regards applications.

Socket weld fittings are not as strong as butt weld connections. As a result, these fittings are usually installed on pipes with relatively small diameters. 

Since butt welded fittings have greater strength, they have more extensive use in high temperature and pressure applications. Butt weld fittings can be utilized where the weld joint strength does not have to be more than the base metal. 

The counterbore in socket welding flanges is slightly bigger than the matching pipe outer diameter. 

Related questions

Why is Weldolet used?

Weldolet has actually become one of the most common of branch links and also can be bonded on the socket pipe. The ends are beveled to promote this procedure, and also, for that reason, the weldolet is thought to be a butt-weld fitting. Weldolets are intended to lower tension levels as well as supply vital support.

Do socket weld flanges have a schedule?

Socket Weld Flanges are available in pressure from 150 # and up and pipeline schedule 40 to schedule 160. Keep in mind; all flanges have a stamping here that shows the size, the pressure rating, the native land, the requirements, the material. A socket weld flange, as you can see right here, has a little socket.

What is a Flexolet?

Flexolet reduces the number of fitting sizes per outlet made possible by the modifications to the MSS specification. Flexolet is utilized widely abroad recently. It is used to connect the enhanced fittings. It takes the place of standard connecting methods. The body of Flexolet Threaded is made in excellent Forgings.

About Pierre Young

Photo of author
Hey, I'm Pierre Young a qualified AWS Certified Welder. I got into welding in 2009 as a side hustle. Ever since then, I've been doing all kinds of welds - both for business and pleasure. While immersing myself in this wonderful hobby, I've learned from hands-on experience what welding gear works and what doesn't. Welding Headquarters is the site where I share everything I've learned.

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