20 inch class 150 flange: dimensions, bolt circle and drilling (ASME B16.5)
The 20 inch class 150 flange to ASME B16.5 is 27.5 in (698.5 mm) across, with 20 holes of 1.25 in (31.8 mm) on a 25 in (635 mm) bolt circle, for 1-1/8 in bolts; the pipe is 20 in (508 mm) outside. The holes straddle the centre lines, the first one 9° off, and the chord between neighbouring holes, which is the divider setting for stepping the drilling out, is 3.91 in (99.3 mm).
Dimensions
| Outside diameter | 27.5 in (698.5 mm) |
|---|---|
| Bolt circle (PCD) | 25 in (635 mm) |
| Number of holes | 20 |
| Hole diameter | 1.25 in (31.8 mm) |
| Bolts | 1-1/8 in |
| Pipe outside diameter | 20 in (508 mm) |
| Angle between holes | 18° |
| First hole from the centre line | 9° |
| Chord between neighbouring holes | 3.91 in (99.3 mm) |
Draw this flange: 1:1 template and DXF
Hole coordinates
From the centre of the flange, in mm, with the first hole 9° off the horizontal axis and the others counter-clockwise, as the standards lay the drilling out.
| Hole | Angle | x (mm) | y (mm) |
|---|---|---|---|
| 1 | 9° | 313.6 | 49.7 |
| 2 | 27° | 282.9 | 144.1 |
| 3 | 45° | 224.5 | 224.5 |
| 4 | 63° | 144.1 | 282.9 |
| 5 | 81° | 49.7 | 313.6 |
| 6 | 99° | -49.7 | 313.6 |
| 7 | 117° | -144.1 | 282.9 |
| 8 | 135° | -224.5 | 224.5 |
| 9 | 153° | -282.9 | 144.1 |
| 10 | 171° | -313.6 | 49.7 |
| 11 | 189° | -313.6 | -49.7 |
| 12 | 207° | -282.9 | -144.1 |
| 13 | 225° | -224.5 | -224.5 |
| 14 | 243° | -144.1 | -282.9 |
| 15 | 261° | -49.7 | -313.6 |
| 16 | 279° | 49.7 | -313.6 |
| 17 | 297° | 144.1 | -282.9 |
| 18 | 315° | 224.5 | -224.5 |
| 19 | 333° | 282.9 | -144.1 |
| 20 | 351° | 313.6 | -49.7 |
Questions
- How many bolts does a %{size} %{class} flange have?
- %{holes}, of %{bolt}, through holes of %{hole} on a %{circle} bolt circle.
- What is the bolt circle of a %{size} %{class} flange?
- %{circle}. The holes are %{angle}° apart, and the first one sits %{half}° off the centre line, so that two flanges mate in any symmetric position. The chord between neighbouring holes is %{chord}.
- Can a %{size} %{class} flange be cut from plate?
- As a plate flange, for low pressure: ducts, tanks, water lines. The outline and the drilling above are what the flange calculator draws, with the 1:1 template and the DXF for plasma or laser. A pressure flange to %{standard} is forged, with a hub and a raised face, and its thickness and facing come from the standard.