Slip-On Flange — Pipe Setback Table
Inside fillet weld setback from flange bore face. Governs pipe cut length for spool fabrication.
Governing Formula
Setback = max(3 mm, 1.5 × WT) → rounded up to nearest 1 mm
Cut deduction: Lcut = F–F − 2 × Setback
SCH 10SCH 40SCH 80
| NPS | DN | SCH 10 | SCH 40 | SCH 80 | |||
|---|---|---|---|---|---|---|---|
| WT (mm) | Setback | WT (mm) | Setback | WT (mm) | Setback | ||
| 1" | DN25 | 2.77 | 5 mm | 3.38 | 6 mm | 4.55 | 7 mm |
| 1¼" | DN32 | 2.77 | 5 mm | 3.56 | 6 mm | 4.85 | 8 mm |
| 1½" | DN40 | 2.77 | 5 mm | 3.68 | 6 mm | 5.08 | 8 mm |
| 2" | DN50 | 2.77 | 5 mm | 3.91 | 6 mm | 5.54 | 9 mm |
| 2½" | DN65 | 3.05 | 5 mm | 5.16 | 8 mm | 7.01 | 11 mm |
| 3" | DN80 | 3.05 | 5 mm | 5.49 | 9 mm | 7.62 | 12 mm |
| 4" | DN100 | 3.05 | 5 mm | 6.02 | 10 mm | 8.56 | 13 mm |
| 6" | DN150 | 3.40 | 6 mm | 7.11 | 11 mm | 10.97 | 17 mm |
| 8" | DN200 | 3.76 | 6 mm | 8.18 | 13 mm | 12.70 | 20 mm |
| 10" | DN250 | 4.19 | 7 mm | 9.27 | 14 mm | 12.70 | 20 mm |
| 12" | DN300 | 4.57 | 7 mm | 9.53 | 15 mm | 12.70 | 20 mm |
Total Cut Deduction
For a spool with slip-on flanges at both ends, the total cut deduction is 2 × Setback. For example, a 4″ SCH 40 pipe (setback = 10 mm) between two flanges at 1000 mm face-to-face would be cut to 1000 − 20 = 980 mm.
Minimum Floor
The 3 mm minimum governs only for very thin-wall pipe (WT < 2 mm), which is uncommon in carbon steel. In practice, the 1.5 × WT rule controls for all schedules listed here.
