DN65 / ANSI 2½″ — Flange Compatibility Solution
Bored blind flanges for mating EN 1092-1 DN65 bolt patterns with ANSI NPS 2½″ pipe
The Problem
EN 1092-1 DN65 slip-on flanges (Type 01) are bored for 76.1 mm OD pipe per EN 10220. ANSI NPS 2½″ pipe has an OD of 73.03 mm (2.875″). The difference of 3.07 mm leaves a gap too large for a sound fillet weld on a standard slip-on flange.
| Standard | Size | Pipe OD |
|---|---|---|
| EN 10220 | DN65 | 76.1 mm |
| ASME B36.10M | NPS 2½″ | 73.03 mm |
| Mismatch | 3.07 mm |
A 3 mm annular gap between the pipe OD and the flange bore prevents a proper root pass on the inside fillet weld. The pipe sits off-centre and the weld pool bridges air instead of metal.
The Solution
Use an EN 1092-1 blind flange (Type 05) bored to fit ANSI NPS 2½″ pipe. The bore is machined to 74.5 mm with a 45° lead-in chamfer, giving approximately 0.7 mm radial clearance — correct for a butt-weld or socket-type fit-up.
Bore Details
- Bore diameter: 74.5 mm
- Chamfer: 45° lead-in at bore face
- Radial clearance on pipe: ≈ 0.7 mm
Unchanged from Standard Type 05
- Flange OD (D)
- Bolt circle diameter (BCD / D1)
- Bolt holes (number, size)
- Raised face OD and height
- Disc thickness (b)
Dimensional Data
All dimensions in millimetres. Each row is a standard EN 1092-1 DN65 blind flange with only the bore modified.
| PN Rating | Flange OD | BCD | Bolts | Bolt hole ∅ | Thickness b | RF OD | RF height | Bore ∅ |
|---|---|---|---|---|---|---|---|---|
| PN10 | 185 | 145 | 4 | 18 | 18 | 122 | 2 | 74.5 |
| PN16 | 185 | 145 | 8 | 18 | 18 | 122 | 2 | 74.5 |
| PN25 | 185 | 145 | 8 | 18 | 22 | 122 | 2 | 74.5 |
| PN40 | 185 | 145 | 8 | 18 | 22 | 122 | 3 | 74.5 |
| PN63 | 205 | 160 | 8 | 22 | 26 | 122 | 3 | 74.5 |
| PN100 | 220 | 170 | 8 | 26 | 30 | 122 | 3 | 74.5 |
Downloads
Free STEP files (AP214) for each pressure class, plus a combined PDF drawing.
