Straight pipe lengths for ISO 5167 flow meters
An orifice plate, nozzle or Venturi tube needs a length of straight pipe before and after it, or the flow profile it sees is not the one its discharge coefficient was measured with. These are the minimum lengths from ISO 5167, in pipe diameters D, for each upstream fitting and diameter ratio β.
How to read the tables
- Each value is a multiple of the pipe's internal diameter D. A value of 22 in a 150 mm pipe means 3.3 m.
- 0 % is the length with no additional uncertainty. 0.5 % is a shorter length allowed if you add 0.5 % to the uncertainty of the discharge coefficient.
- Find the column for your β. Between two columns, use the larger β: it gives the longer, safer length.
- A dash means the standard gives no shorter length for 0.5 %.
FlowCalc does this lookup for you. The PDF report for each device lists every fitting with the lengths worked out for its β and pipe size, in your length unit.
Orifice plates
ISO 5167-2:2003, Table 3
| Upstream fitting | β ≤ | 0.20 | 0.40 | 0.50 | 0.60 | 0.67 | 0.75 |
|---|---|---|---|---|---|---|---|
| 1. Single 90° bend, or two 90° bends in any plane (S > 30D) | 0 % | 6 | 16 | 22 | 42 | 44 | 44 |
| 0.5 % | 3 | 3 | 9 | 13 | 20 | 20 | |
| 2. Two 90° bends in the same plane, S configuration (30D ≥ S > 10D) | 0 % | 10 | 10 | 18 | 30 | 44 | 44 |
| 0.5 % | – | – | 10 | 18 | 18 | 18 | |
| 3. Two 90° bends in the same plane, S configuration (10D ≥ S ≥ 5D) | 0 % | 10 | 10 | 22 | 42 | 44 | 44 |
| 0.5 % | – | – | 10 | 18 | 20 | 22 | |
| 4. Two 90° bends in perpendicular planes (30D ≥ S ≥ 5D) | 0 % | 19 | 44 | 44 | 44 | 44 | 44 |
| 0.5 % | 18 | 18 | 18 | 18 | 20 | 20 | |
| 5. Two 90° bends in perpendicular planes (S < 5D) | 0 % | 34 | 50 | 75 | 65 | 60 | 75 |
| 0.5 % | 17 | 25 | 34 | 25 | 18 | 18 | |
| 6. Single 90° tee with or without an extension, mitre 90° bend | 0 % | 3 | 9 | 19 | 29 | 36 | 44 |
| 0.5 % | – | 3 | 9 | 18 | 18 | 18 | |
| 7. Single 45° bend, or two 45° bends in the same plane, S configuration (S ≥ 2D) | 0 % | 7 | 30 | 30 | 30 | 44 | 44 |
| 0.5 % | – | 9 | 18 | 18 | 18 | 18 | |
| 8. Concentric reducer 2D to D over a length of 1.5D to 3D | 0 % | 5 | 5 | 8 | 9 | 12 | 13 |
| 0.5 % | – | – | 5 | 5 | 6 | 8 | |
| 9. Concentric expander 0.5D to D over a length of D to 2D | 0 % | 6 | 12 | 20 | 26 | 28 | 36 |
| 0.5 % | – | 8 | 9 | 11 | 14 | 18 | |
| 10. Full bore ball or gate valve, fully open | 0 % | 12 | 12 | 12 | 14 | 18 | 24 |
| 0.5 % | 6 | 6 | 6 | 7 | 9 | 12 | |
| 11. Abrupt symmetrical reduction | 0 % | 30 | 30 | 30 | 30 | 30 | 30 |
| 0.5 % | 15 | 15 | 15 | 15 | 15 | 15 | |
| 12. Thermometer pocket or well, diameter ≤ 0.03D | 0 % | 5 | 5 | 5 | 5 | 5 | 5 |
| 0.5 % | 3 | 3 | 3 | 3 | 3 | 3 | |
| Downstream, any fitting in this table | 0 % | 4 | 6 | 6 | 7 | 7 | 8 |
| 0.5 % | 2 | 3 | 3 | 3.5 | 3.5 | 4 |
S is the separation between two bends, from the downstream end of the curved part of the upstream bend to the upstream end of the curved part of the downstream bend.
Nozzles and Venturi nozzles
ISO 5167-3:2003
| Upstream fitting | β ≤ | 0.20 | 0.25 | 0.30 | 0.35 | 0.40 | 0.45 | 0.50 | 0.55 | 0.60 | 0.65 | 0.70 | 0.75 | 0.80 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1. Single 90° bend or tee (flow from one branch only) | 0 % | 10 | 10 | 10 | 12 | 14 | 14 | 14 | 16 | 18 | 22 | 28 | 36 | 46 |
| 0.5 % | 6 | 6 | 6 | 6 | 7 | 7 | 7 | 8 | 9 | 11 | 14 | 18 | 23 | |
| 2. Two or more 90° bends in the same plane | 0 % | 14 | 14 | 16 | 16 | 18 | 18 | 20 | 22 | 26 | 32 | 36 | 42 | 50 |
| 0.5 % | 7 | 7 | 8 | 8 | 9 | 9 | 10 | 11 | 13 | 16 | 18 | 21 | 25 | |
| 3. Two or more 90° bends in different planes | 0 % | 34 | 34 | 34 | 36 | 36 | 38 | 40 | 44 | 48 | 54 | 62 | 70 | 80 |
| 0.5 % | 17 | 17 | 17 | 18 | 18 | 19 | 20 | 22 | 24 | 27 | 31 | 35 | 40 | |
| 4. Reducer 2D to D over a length of 1.5D to 3D | 0 % | 5 | 5 | 5 | 5 | 5 | 5 | 6 | 8 | 9 | 11 | 14 | 22 | 30 |
| 0.5 % | – | – | – | – | – | – | 5 | 5 | 5 | 6 | 7 | 11 | 15 | |
| 5. Expander 0.5D to D over a length of D to 2D | 0 % | 16 | 16 | 16 | 16 | 16 | 17 | 18 | 20 | 22 | 25 | 30 | 38 | 54 |
| 0.5 % | 8 | 8 | 8 | 8 | 8 | 9 | 9 | 10 | 11 | 13 | 15 | 19 | 27 | |
| 6. Globe valve, fully open | 0 % | 18 | 18 | 18 | 18 | 20 | 20 | 22 | 24 | 26 | 28 | 32 | 36 | 44 |
| 0.5 % | 9 | 9 | 9 | 9 | 10 | 10 | 11 | 12 | 13 | 14 | 16 | 18 | 22 | |
| 7. Full bore ball or gate valve, fully open | 0 % | 12 | 12 | 12 | 12 | 12 | 12 | 12 | 14 | 14 | 16 | 20 | 24 | 30 |
| 0.5 % | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 7 | 7 | 8 | 10 | 12 | 15 | |
| 8. Abrupt symmetrical reduction | 0 % | 30 | 30 | 30 | 30 | 30 | 30 | 30 | 30 | 30 | 30 | 30 | 30 | 30 |
| 0.5 % | 15 | 15 | 15 | 15 | 15 | 15 | 15 | 15 | 15 | 15 | 15 | 15 | 15 | |
| 9. Thermometer pocket or well, diameter ≤ 0.03D | 0 % | 5 | 5 | 5 | 5 | 5 | 5 | 5 | 5 | 5 | 5 | 5 | 5 | 5 |
| 0.5 % | 3 | 3 | 3 | 3 | 3 | 3 | 3 | 3 | 3 | 3 | 3 | 3 | 3 | |
| 10. Thermometer pocket or well, 0.03D < diameter ≤ 0.13D | 0 % | 20 | 20 | 20 | 20 | 20 | 20 | 20 | 20 | 20 | 20 | 20 | 20 | 20 |
| 0.5 % | 10 | 10 | 10 | 10 | 10 | 10 | 10 | 10 | 10 | 10 | 10 | 10 | 10 | |
| Downstream, fittings 1 to 7 | 0 % | 4 | 4 | 5 | 5 | 6 | 6 | 6 | 6 | 7 | 7 | 7 | 8 | 8 |
| 0.5 % | 2 | 2 | 2.5 | 2.5 | 3 | 3 | 3 | 3 | 3.5 | 3.5 | 3.5 | 4 | 4 |
Applies to ISA 1932 nozzles, long radius nozzles and Venturi nozzles.
Classical Venturi tubes
ISO 5167-4:2003, Table 1
| Upstream fitting | β ≤ | 0.30 | 0.40 | 0.50 | 0.60 | 0.70 | 0.75 |
|---|---|---|---|---|---|---|---|
| 1. Single 90° bend | 0 % | 8 | 8 | 9 | 10 | 14 | 16 |
| 0.5 % | 3 | 3 | 3 | 3 | 3 | 8 | |
| 2. Two or more 90° bends in the same or different planes | 0 % | 8 | 8 | 10 | 10 | 18 | 22 |
| 0.5 % | 3 | 3 | 3 | 3 | 3 | 8 | |
| 3. Reducer 1.33D to D over a length of 2.3D | 0 % | 4 | 4 | 4 | 4 | 4 | 4 |
| 0.5 % | – | – | – | – | – | – | |
| 4. Expander 0.67D to D over a length of 2.5D | 0 % | 4 | 4 | 5 | 6 | 7 | 7 |
| 0.5 % | – | – | 4 | 4 | 5 | 6 | |
| 5. Reducer 3D to D over a length of 3.5D | 0 % | 2.5 | 2.5 | 5.5 | 8.5 | 10.5 | 11.5 |
| 0.5 % | – | – | 2.5 | 2.5 | 2.5 | 3.5 | |
| 6. Expander 0.75D to D over a length of D | 0 % | 2.5 | 2.5 | 2.5 | 3.5 | 5.5 | 6.5 |
| 0.5 % | – | – | – | 2.5 | 3.5 | 4.5 | |
| 7. Full bore ball or gate valve, fully open | 0 % | 2.5 | 2.5 | 3.5 | 4.5 | 5.5 | 5.5 |
| 0.5 % | – | – | 2.5 | 2.5 | 3.5 | 3.5 |
Downstream, a fitting at least 4 throat diameters after the throat tapping does not affect the measurement.
Size the meter, get the lengths
Enter the pipe, the fluid and the flow, and FlowCalc solves the bore, flow or ΔP to ISO 5167. The report lists the straight lengths for that β and pipe, in metres or feet.