A factor used in a sizing system for certain types of plastic pipe.
For pipes manufactured with controlled outer diameters, the SDR is the ratio of the average specified outside diameter to the minimum specified wall thickness. If using an SDR value to calculate minimum wall thickness gives a thickness of less than 0.060 inches (1.52 millimeters), the thickness is arbitrarily set at 0.060 inches (1.52 millimeters).
For pipes manufactured with controlled inner diameters, the SIDR is the ratio of the average specified inside diameter to the minimum specified wall thickness.
The SDR and SIDT magnitudes are based on the ANSI series of preferred numbers. SDR values are a preferred number plus 1, and SIDR values are a preferred number minus 1, thusly:
| ANSI preferred numbers, series 10* |
SDR | SIDR |
|---|---|---|
| 5.0 | 6.0 | 4.0 |
| 6.3‡ | 7.3 | 5.3 |
| 8.0 | 9.0 | 7.0 |
| 10.0 | 11.0 | 9.0 |
| 12.5 | 13.5 | 11.5 |
| 16.0 | 17.0 | 15.0 |
| 20.0 | 21.0 | 19.0 |
| 25.0 | 26.0 | 24.0 |
| 31.5 | 32.5 | 30.5 |
| 40.0 | 41.0 | 39.0 |
| 50.0 | 51.0 | 49.0 |
| 63.0 | 64.0 | 62.0 |
* ANSI Z17.1, Preferred Numbers. The same sequence is specified as R 10 in ISO 3 and ISO 497.
‡ While several standards (e.g., those listed below) call for rounding all SDR values to the nearest 0.5, ASTM itself does not do this for the values based on 6.3.
Some examples of standards employing the SDR system:
ASTM D 2241-09. Standard Specification for Poly(Vinyl Chloride) (PVC) Pressure-Rated Pipe (SDR Series). Includes SDR's 11, 13.5, 17, 21, 26, 32.5, 35, 41, 51, 64 and 81.
ASTM D 2282-99 (Reapproved 2005). Standard Specification for Acrylonitrile-Butadiene-Styrene (ABS) Plastic Pipe (SDR-PR). (Withdrawn 2007) Includes SDR's 13.5, 17, 21 and 26.
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Last revised: 27 August 2011.