Socket Weld Fitting

Written by Matt Milbury on 10 January 2016. Posted in Pipe Fitting

A socket weld pipe fitting, abbreviated as SWF, is one where the pipe is inserted into a recessed area of the fitting. To make a socket weld fitting, the pipe is inserted into the pipe before it is welded. In order to prevent damage to the pipe and fitting, the pipe is then backed out a minimum of 1/16” to allow for thermal expansion of the pipe during the welding procedure. If this clearance is not made, the weld can crack due to the pipe expanding against the fitting.

Socket weld flange with pipeSW fittings are used for piping that has a nominal pipe size (NPS) of 3 inches and below.

Non metallic pipe almost exclusively uses sock-weld fittings for their permanent connections. This is because the socket gives ample surface area for the glue to bond the two pieces together.

One of the benefits of using these types of fittings is that the end of the pipe doesn't need to be beveled before welding. That is, the pipe end is a plain end instead of a bevel end. This means that it uses a single fillet weld as opposed to a butt weld. This means that the pipe fitter can install and weld without having to have a special clamp or tack welding, which is the case with butt welded pipe.

Because a fillet weld is used instead of a butt weld, there is no possibility for weld metal to enter the bore of the pipe. Because a fillet weld is used, it can only be inspected by using non radiographic methods, such as magnetic particle or liquid dye penetrant methods.

There are also some shortfalls in using socket weld fittings. If the welder does not leave a gap between the pipe and the shoulder of the socket, there is a risk that the weld will fail either during the welding process or under high temperatures.

This gap can cause solids to accumulate which can cause corrosion issues. If the piping is used for multiple process fluids, this accumulation may contaminate the additional process streams.

There are three different pressure classes available for socket welded, 3000, 6000 and 9000. In general, Class 3000 is for use with Schedule 80 pipe, 6000 - Schedule 160 and 9000 – XXH. The pressure classes are based on the cold working pressure limits of 3000, 6000 and 9000 psi.

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Forged Fittings Socket and Threaded Types

Pressure Class	2000	3000	6000	9000
Socket Fitting	-	80/XH	160	XXH
Threaded Fitting	80/XH	160	XXH	-

Note: Class designations correspond to the maximum cold working pressure of fittings in pounds force per square inch.

The following links are for datasheets for the socket fitting range sizes covered by ASME B16.11. If you would like to browse the datasheets for pipe fittings, please visit our Fittings Datasheets page.

Fitting	3000	6000	9000
45 Elbow	1/8 - 4	1/8 - 2	1/2 - 2
90 Elbow	1/8 - 4	1/8 - 2	1/2 - 2
Cap, Round	1/8 - 4	1/8 - 2	1/2 - 2
Coupling, Full	1/8 - 4	1/8 - 2	1/2 - 2
Coupling, Half	1/8 - 4	1/8 - 2	1/2 - 2
Cross	1/8 - 4	1/8 - 2	1/2 - 2
Lateral	3/8 - 2	3/8 - 1 1/2	1/2 - 1 1/2
Reducer	1/8 - 4	1/2 - 4	1/2 - 2
Tee	1/8 - 4	1/2 - 4	1/2 - 2
Union	1/8 - 3	1/8 - 2	-

Notes:

Dimension tolerances in accordance with ANSI/ASME B16.11 do not include laterals, reducers and unions.
Fittings with special dimensions, threads, or counterbores can be made by agreement between the manufacturer and purchaser. If the fittings meet all of the requirements of this Standard, they can be considered in compliance, provided they are appropriately marked.