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Flanges - ASME/ANSI B16.5 Flanges and Bolt Dimensions - Class 150 to 2500

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Flange dimensions are determined by the pipe size and the pressure class required for the application. Flanges are standardized according publications from organizations like ASME, MSS, API and others.

ASME/ANSI B16.5 provides

  • weld neck
  • slip-on
  • socket weld
  • threaded
  • lap joint
  • blind

flange dimensions for pipes ranging 1/2" to 24" - in classes ranging 150 to 2500. Note that the ratings are in steps with terminology like ASME class xxx or API xxxx.

In general you need to specify the schedule (thickness) of the connected pipe when it is being butt welded to the flange. Socket welded and threaded connections is unaffected by wall thickness and should only require the OD.

ASME/ANSI B16.5 Flanges and Bolt Dimensions - Class 150
Nominal Pipe Size
NPS
(inches)
Class 150
Diameter of
Flange
(inches)
No.
of
Bolts
Diameter of
Bolts
(inches)
Diameter of
Bolt Holes
(inches)
Bolt
Circle
(inches)
1/4 3-3/8 4 1/2 0.62 2-1/4
1/2 3-1/2 4 1/2 0.62 2-3/8
3/4 3-7/8 4 1/2 0.62 2-3/4
1 4-1/4 4 1/2 0.62 3-1/8
1-1/4 4-5/8 4 1/2 0.62 3-1/2
1-1/2 5 4 1/2 0.62 3-7/8
2 6 4 5/8 0.75 4-3/4
2-1/2 7 4 5/8 0.75 5-1/2
3 7-1/2 4 5/8 0.75 6
3-1/2 8-1/2 8 5/8 0.75 7
4 9 8 5/8 0.75 7-1/2
5 10 8 3/4 0.88 8-1/2
6 11 8 3/4 0.88 9-1/2
8 13-1/2 8 3/4 0.88 11-3/4
10 16 12 7/8 1 14-1/4
12 19 12 7/8 1 17
14 21 12 1 1.12 18-3/4
16 23-1/2 16 1 1.12 21-1/4
18 25 16 1-1/8 1.25 22-3/4
20 27-1/2 20 1-1/8 1.25 25
24 32 20 1-1/4 1.38 29-1/2
  • 1 inch = 25.4 mm
ASME/ANSI B16.5 Flanges and Bolt Dimensions - Class 300
Nominal Pipe Size
NPS
(inches)
Class 300
Diameter of
Flange
(inches)
No.
of
Bolts
Diameter of
Bolts
(inches)
Diameter of
Bolt Holes
(inches)
Bolt
Circle
(inches)
1/4 3-3/8 4 1/2 0.62 2-1/4
1/2 3-3/4 4 1/2 0.62 2-5/8
3/4 4-5/8 4 5/8 0.75 3-1/4
1 4-7/8 4 5/8 0.75 3-1/2
1-1/4 5-1/4 4 5/8 0.75 3-7/8
1-1/2 6-1/8 4 3/4 0.88 4-1/2
2 6-1/2 8 5/8 0.75 5
2-1/2 7-1/2 8 3/4 0.88 5-7/8
3 8-1/4 8 3/4 0.88 6-5/8
3-1/2 9 8 3/4 0.88 7-1/4
4 10 8 3/4 0.88 7-7/8
5 11 8 3/4 0.88 9-1/4
6 12-1/2 12 3/4 0.88 10-5/8
8 15 12 7/8 1 13
10 17-1/2 16 1 1.12 15-1/4
12 20-1/2 16 1-1/8 1.25 17-3/4
14 23 20 1-1/8 1.25 20-1/4
16 25-1/2 20 1-1/4 1.38 22-1/2
18 28 24 1-1/4 1.38 24-3/4
20 30-1/2 24 1-1/4 1.38 27
24 36 24 1-1/2 1.62 32
ASME/ANSI B16.5 Flanges and Bolt Dimensions - Class 400
Nominal Pipe Size
NPS
(inches)
Class 400
Diameter of
Flange
(inches)
No.
of
Bolts
Diameter of
Bolts
(inches)
Diameter of
Bolt Holes
(inches)
Bolt
Circle
(inches)
1/4 3-3/8 4 1/2 0.62 2-1/4
1/2 3-3/4 4 1/2 0.62 2-5/8
3/4 4-5/8 4 5/8 0.75 3-1/4
1 4-7/8 4 5/8 0.75 3-1/2
1-1/4 5-1/4 4 5/8 0.75 3-7/8
1-1/2 6-1/8 4 3/4 0.88 4-1/2
2 6-1/2 8 5/8 0.75 5
2-1/2 7-1/2 8 3/4 0.88 5-7/8
3 8-1/4 8 3/4 0.88 6-5/8
3-1/2 9 8 7/8 1 7-1/4
4 10 8 7/8 1 7-7/8
5 11 8 7/8 1 9-1/4
6 12-1/2 12 7/8 1 10-5/8
8 15 12 1 1.12 13
10 17-1/2 16 1-1/8 1.25 15-1/4
12 20-1/2 16 1-1/4 1.38 17-3/4
14 23 20 1-1/4 1.38 20-1/4
16 25-1/2 20 1-3/8 1.5 22-1/2
18 28 24 1-3/8 1.5 24-3/4
20 30-1/2 24 1-1/2 1.62 27
24 36 24 1-3/4 1.88 32
ASME/ANSI B16.5 Flanges and Bolt Dimensions - Class 600
Nominal Pipe Size
NPS
(inches)
Class 600
Diameter of
Flange
(inches)
No.
of
Bolts
Diameter of
Bolts
(inches)
Diameter of
Bolt Holes
(inches)
Bolt
Circle
(inches)
1/4 3-3/8 4 1/2 0.62 2-1/4
1/2 3-3/4 4 1/2 0.62 2-5/8
3/4 4-5/8 4 5/8 0.75 3-1/4
1 4-7/8 4 5/8 0.75 3-1/2
1-1/4 5-1/4 4 5/8 0.75 3-7/8
1-1/2 6-1/8 4 3/4 0.88 4-1/2
2 6-1/2 8 5/8 0.75 5
2-1/2 7-1/2 8 3/4 0.88 5-7/8
3 8-1/4 8 3/4 0.88 6-5/8
3-1/2 9 8 7/8 1 7-1/4
4 10-3/4 8 7/8 1 8-1/2
5 13 8 1 1.12 10-1/2
6 14 12 1 1.12 11-1/2
8 16-1/2 12 1-1/8 1.25 13-3/4
10 20 16 1-1/4 1.38 17
12 22 20 1-1/4 1.38 19-1/4
14 23-3/4 20 1-3/8 1.5 20-3/4
16 27 20 1-1/2 1.62 23-3/4
18 29-1/4 20 1-5/8 1.75 25-3/4
20 32 24 1-5/8 1.75 28-1/2
24 37 24 1-7/8 2 33
ASME/ANSI B16.5 Flanges and Bolt Dimensions - Class 900
Nominal Pipe Size
NPS
(inches)
Class 900
Diameter of
Flange
(inches)
No.
of
Bolts
Diameter of
Bolts
(inches)
Diameter of
Bolt Holes
(inches)
Bolt
Circle
(inches)
1/2 4-3/4 4 3/4 0.88 3-1/4
3/4 5-1/8 4 3/4 0.88 3-1/2
1 5-7/8 4 7/8 1 4
1-1/4 6-1/4 4 7/8 1 4-3/8
1-1/2 7 4 1 1.12 4-7/8
2 8-1/2 8 7/8 1 6-1/2
2-1/2 9-5/8 8 1 1.12 7-1/2
3 9-1/2 8 7/8 1 7-1/2
4 11-1/2 8 1-1/8 1.25 9-1/4
5 13-3/4 8 1-1/4 1.38 11
6 15 12 1-1/8 1.25 12-1/2
8 18-1/2 12 1-3/8 1.5 15-1/2
10 21-1/2 16 1-3/8 1.5 18-1/2
12 24 20 1-3/8 1.5 21
14 25-1/4 20 1-1/2 1.62 22
16 27-3/4 20 1-5/8 1.75 24-1/2
18 31 20 1-7/8 2 27
20 33-3/4 20 2 2.12 29-1/2
24 41 20 2-1/2 2.62 35-1/2
ASME/ANSI B16.5 Flanges and Bolt Dimensions - Class 1500
Nominal Pipe Size
NPS
(inches)
Class 1500
Diameter of
Flange
(inches)
No.
of
Bolts
Diameter of
Bolts
(inches)
Diameter of
Bolt Holes
(inches)
Bolt
Circle
(inches)
1/2 4-3/4 4 3/4 0.88 3-1/4
3/4 5-1/8 4 3/4 0.88 3-1/2
1 5-7/8 4 7/8 1 4
1-1/4 6-1/4 4 7/8 1 4-3/8
1-1/2 7 4 1 1.12 4-7/8
2 8-1/2 8 7/8 1 6-1/2
2-1/2 9-5/8 8 1 1.12 7-1/2
3 10-1/2 8 1-1/8 1.25 8
4 12-1/4 8 1-1/4 1.38 9-1/2
5 14-3/4 8 1-1/2 1.62 11-1/2
6 15-1/2 12 1-3/8 1.5 12-1/2
8 19 12 1-5/8 1.75 15-1/2
10 23 12 1-7/8 2 19
12 26-1/2 16 2 2.12 22-1/2
14 29-1/2 16 2-1/4 2.38 25
16 32-1/2 16 2-1/2 2.62 27-3/4
18 36 16 2-3/4 2.88 30-1/2
20 38-3/4 16 3 3.12 32-3/4
24 46 16 3-1/2 3.62 39
ASME/ANSI B16.5 Flanges and Bolt Dimensions - Class 2500
Nominal Pipe Size
NPS
(inches)
Class 2500
Diameter of
Flange
(inches)
No.
of
Bolts
Diameter of
Bolts
(inches)
Diameter of
Bolt Holes
(inches)
Bolt
Circle
(inches)
1/2 5-1/4 4 3/4 0.88 3-1/2
3/4 5-1/2 4 3/4 0.88 3-3/4
1 6-1/4 4 7/8 1 4-1/4
1-1/4 7-1/4 4 1 1.12 5-1/8
1-1/2 8 4 1-1/8 1.25 5-3/4
2 9-1/4 8 1 1.12 6-3/4
2-1/2 10-1/2 8 1-1/8 1.25 7-3/4
3 12 8 1-1/4 1.38 9
4 14 8 1-1/2 1.62 10-3/4
5 16-1/2 8 1-3/4 1.88 12-3/4
6 19 8 2 2.12 14-1/2
8 21-3/4 12 2 2.12 17-1/4
10 26-1/2 12 2-1/2 2.62 21-1/4
12 30 12 2-3/4 2.88 24-3/8

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