Socket Weld Flange Dimensions

The pipe drops into a counterbored socket and is fillet-welded on the outside only. Published in NPS 1/2 through NPS 3 in Classes 150, 300 and 600 and through NPS 2 1/2 in Classes 400 and 1500; the small-bore equivalent of a slip-on.

Standard: ASME B16.5
Abbreviation: SW
Pressure classes: 5
Size range: NPS 1/2 – NPS 3
Typical service: Small-bore high-pressure lines: instrument, hydraulic and steam trace piping.

Socket Weld Flange in section, and a Class 150 flange from the front. The section shows what each column of the dimension tables measures, with welds in orange; it is not to scale. The front view is an NPS 6 Class 150 flange drawn to scale, with its bolt holes straddling the centrelines.

Dimensions by pressure class

Class 150NPS 1/2 – 38 sizes Class 300NPS 1/2 – 38 sizes Class 400NPS 1/2 – 2 1/27 sizes Class 600NPS 1/2 – 38 sizes Class 1500NPS 1/2 – 2 1/27 sizes

Strengths

Good static strength in small bore, and easy to fit up
No weld metal can protrude into the bore

Limitations

Needs a 1/16 in expansion gap at the socket bottom to avoid weld cracking
The gap is a crevice — poor choice for corrosive or sanitary service

Class 150 dimensions

Dimensions are given in inches, with the millimetre equivalent beneath in grey.

ASME B16.5 Class 150 socket weld flange dimensions — the most commonly specified class.
Size	Flange OD	Thickness	Bolt circle	Bolts	Bolt dia.	Raised face OD
NPS 1/2	3.5088.90 mm	0.389.65 mm	2.3860.45 mm	4	1/2 in	1.3835.05 mm
NPS 3/4	3.8898.55 mm	0.4411.18 mm	2.7569.85 mm	4	1/2 in	1.6942.93 mm
NPS 1	4.25107.95 mm	0.5012.70 mm	3.1279.25 mm	4	1/2 in	2.0050.80 mm
NPS 1 1/4	4.62117.35 mm	0.5614.22 mm	3.5088.90 mm	4	1/2 in	2.5063.50 mm
NPS 1 1/2	5.00127.00 mm	0.6215.75 mm	3.8898.55 mm	4	1/2 in	2.8873.15 mm
NPS 2	6.00152.40 mm	0.6917.53 mm	4.75120.65 mm	4	5/8 in	3.6291.95 mm
NPS 2 1/2	7.00177.80 mm	0.8120.57 mm	5.50139.70 mm	4	5/8 in	4.12104.65 mm
NPS 3	7.50190.50 mm	0.8822.35 mm	6.00152.40 mm	4	5/8 in	5.00127.00 mm

Higher classes are on the Class 300 page and above.

Guides and comparisons for this page

Socket weld vs threaded flangeThe two small-bore options compared.Pipe end connectionsBevelled, plain and threaded ends, and where each is used.Choosing a flange face typeRaised face, flat face or ring-type joint, by service.Flange bolt torqueTarget torque from bolt stress, for every B16.5 bolt size.Pressure-temperature deratingReading a P-T table and interpolating between temperatures.

Common questions

When should I use a socket weld flange?

Small-bore high-pressure lines: instrument, hydraulic and steam trace piping.

What pressure classes does a socket weld flange come in?

ASME B16.5 publishes the socket weld flange in Class 150, Class 300, Class 400, Class 600 and Class 1500, in sizes NPS 1/2 through NPS 3 in Classes 150, 300 and 600 and NPS 2 1/2 in Classes 400 and 1500. It does not publish a socket weld flange in Class 900 or 2500. Above NPS 24 large-diameter flanges are covered by ASME B16.47 instead.

Does the flange face type change these dimensions?

The flange outside diameter, bolt circle and bolting are the same whatever the face. What changes is the facing itself and the flange thickness measurement: B16.5 thickness excludes the raised face, so a Class 300 raised-face flange is 0.06 in thicker overall than the tabulated figure. Ring-type joint flanges are grooved instead and are dimensioned separately.